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Morphological and ultrastructural analysis of Turritopsis nutricula during life cycle reversal


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The hydrozoa life cycle is characterized, in normal conditions, by the alternation of a post-larval benthic polyp and an adult pelagic medusa; however, some species of Hydrozoa react to environmental stress by reverting their life cycle: i.e. an adult medusa goes back to the juvenile stage of polyp. This very uncommon life cycle could be considered as some sort of inverted metamorphosis. A morphological study of different stages during the reverted life cycle of Turritopsis nutricula led to the characterization of four different stages: healthy medusa, unhealthy medusa, four-leaf clover and cyst. The ultrastructural study of the cellular modifications (during the life cycle reversion of T. nutricula) showed the presence of both degenerative and apoptotic processes. Degeneration was prevalent during the unhealthy medusa and four-leaf clover stages, while the apoptotic rate was higher during the healthy medusa and cyst stages. The significant presence of degenerative and apoptotic processes could be related to the occurrence of a sort of metamorphosis when an adult medusa transforms itself into a polyp.
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Tissue & Cell 35 (2003) 213–222
Morphological and ultrastructural analysis of Turritopsis
nutricula during life cycle reversal
E.C. Carla’, P. Pagliara, S. Piraino, F. Boero, L. Dini
Department of Biological and Environmental Science and Technology, University of Lecce, Via per Monteroni, 73100 Lecce, Italy
Received 13 December 2002; received in revised form 28 February 2003; accepted 7 March 2003
The hydrozoa life cycle is characterized, in normal conditions, by the alternation of a post-larval benthic polyp and an adult pelagic
medusa; however, some species of Hydrozoa react to environmental stress by reverting their life cycle: i.e. an adult medusa goes back to the
juvenilestageof polyp. This very uncommon life cyclecouldbe considered as some sort ofinvertedmetamorphosis.Amorphological study
of different stages during the reverted life cycle of Turritopsis nutricula led to the characterization of four different stages: healthy medusa,
unhealthy medusa, four-leaf clover and cyst. The ultrastructural study of the cellular modifications (during the life cycle reversion of T.
nutricula) showed the presence of both degenerative and apoptotic processes. Degeneration was prevalent during the unhealthy medusa
and four-leaf clover stages, while the apoptotic rate was higher during the healthy medusa and cyst stages. The significant presence of
degenerative and apoptotic processes could be related to the occurrence of a sort of metamorphosis when an adult medusa transforms itself
into a polyp.
© 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Hydrozoa; Apoptosis; Lectin-binding sites
1. Introduction
The hydrozoa life cycle is generally characterized by the
alternation of a post-larval benthic polyp and an adult pelagic
medusa; but in some species a reduction or a suppression of
polyp or medusa stage can be observed (Boero and Bouillon,
1993). In a complete cycle, the mature medusa releases ga-
metes into the water where fertilization occurs; while in
species without the medusa stage, gametes develop in spe-
cial structures (gonophores). After a short period of free life,
the resulting planula larva settles and metamorphoses into
a benthic polyp. During metamorphosis there are running
programs which initially strive to reduce all body parts that
are no longer necessary. Afterwards, a distinct turning point
is reached, followed by the subsequent development of fea-
tures, finely represented by a primary polyp (Seipp et al.,
2001). This polyp buds other polyps and forms a colony,
but can also bud medusae that detach themselves from the
colony to spend a free life, until the gametes are released,
after which they die.
Corresponding author. Tel.: +39-0832-298614;
fax: +39-0832-298626.
E-mail address: (L. Dini).
In a normal life cycle, stress (all factors causing change
in a biological system), which is potentially injurious and
whose effects may be lethal or sub-lethal, is considered to
be a disadvantage for animals. However, stress is not always
harmful and may trigger very different biological responses;
indeed a variety of stress responses have been measured
in biological systems exposed to various kinds and intensi-
ties of stress factors (Karlin and Brocchieri, 1998; Kregel,
Among Hydrozoa, some species seem to be able to re-
act to stress in an unexpected way: the medusa drift back
ontogenetically to a polyp, generally considered to be a
juvenile stage (Boero et al., 1997). Turritopsis nutricula
was the first described Hydrozoan species able to revert its
life cycle (Bavestrello et al., 1992). The authors claimed
that the reversion occurred only in young medusae, and not
in sexually mature animals. The medusa, under stressed
conditions, develops back to the polyp stage. During this
reversion cellular reorganization is needed; differentiated
cells return to an undifferentiated stage to change their fate
(Piraino et al., 1996). Indeed, by applying different types
of stresses (changes in temperature, salinity, O2concentra-
tion, lack of food), Piraino et al. (1996) induced reversion
and demonstrated that a set of undifferentiated cells in the
0040-8166/03/$ – see front matter © 2003 Elsevier Science Ltd. All rights reserved.
214 E.C. Carla’ et al./Tissue & Cell 35 (2003) 213–222
transforming medusa produced a polyp; this property has
also been observed during indirect development, when un-
differentiated set aside cells retain the potential to divide
indefinitely and thus to build large structures (Davidson
et al., 1995; Peterson et al., 1997). However, different
mechanisms of differentiation can be evoked to explain the
reverted life cycle in T. nutricula: i.e. some differentiated
cells can also participate in polyp reconstruction, by the
activation of a process similar to metamorphosis.
Metamorphosis generally occurs in those species charac-
terized by indirect development. During this period, in which
a larva transforms itself into an adult, degenerative as well as
apoptotic processes have been described for a wide range of
species: amphibians and insects represent good models for
this (Vogt, 1842; White et al., 1994; Truman, 1984; Sanders
and Wride, 1995). Apoptosis or programmed cell death is a
process fundamental for correct development as well as for
the maintenance of the organism’s integrity by destroying
cells that are potentially harmful. This process may be im-
portant to redefine the body structure of the polyp generated
during the reverted life cycle of T. nutricula.
The present paper describes a morphological study of dif-
ferent stages during the reverted life cycle of T. nutricula,
giving evidence for degenerative and apoptotic processes, as
well as the capacity of the mature medusa to revert.
2. Materials and methods
2.1. Sample
Hydrozoa colonies were collected by scuba diving near
the Cheradi Isles (Mar Piccolo of Taranto, Italy) during
late summer and autumn (from August to November) 1999.
Colonies were kept in aerated sea water and identified in the
laboratory by a stereoscope (Leica MZ12).
Fertile colonies of T. nutricula were isolated and kept
in filtered sea water (FSW) at 22C. The newly generated
medusae were isolated and fed with Artemia naupli. Daily
changes of FSW were performed. Different stresses were
applied to verify the medusae’s capacity to react by reorga-
nizing itself into a polyp. Umbrella excision with scissors,
raising the temperature to 30 C for 30min or oxygen reduc-
tion by adding to large a quantity of nauplia were applied.
2.2. Transmission electron microscopy (TEM)
Different stages of T. nutricula fixed in 2.5% glutaralde-
hyde sea water solution for 2h at ice temperature were
washed three times in FSW. Post-fixation was performed
with 1% OsO4in FSW for 1h. Samples were then washed
several times in FSW and dehydrated with increasing con-
centration of alcohol for 30min each at room tempera-
ture, then embedded in epoxy resin. Ultra-thin sections were
stained with uranyl acetate and lead citrate and examined
under a Philips CM12 TEM.
2.3. Scanning electron microscopy (SEM)
Different stages of T. nutricula were fixed in 2.5% glu-
taraldehyde and post-fixed in 1% OsO4in FSW as described
above. They were dehydrated with acetone, desiccated with
2Critical Point Dryer 020 (Balzer, Liechtenstein), spat-
tered with gold (Coated 040 Balzer) and observed under a
Philips XL50 scanning microscope.
2.4. Confocal microscopy
Different stages of T. nutricula were fixed in 4% buffered
paraformaldehyde and embedded in paraffin; 3-m thick
sections were analyzed by using FITC-conjugated lectins.
The following lectins were used (the concentrations and the
sugar specificities are given in brackets): Ulex europaeus
(40g/ml, -fucose); Concanavlin-A (ConA; 40g/ml,
mannose); Ricinus (2g/ml, -gal). All lectins were pur-
chased from Sigma (St. Louis, MO, USA).
Surface sugar localization was investigated by using a
Nikon PCM 2000 microscope (Nikon, Japan) with Plan
Fluor objectives (Nikon, Japan). Confocal microscopy was
performed utilizing a confocal laser scanning head Nikon
PCM 2000 based on a Nikon Eclipse 600 microscope. Ac-
quisition and visualization are completely computer con-
trolled through the EZ 2000 software (Coord-Nikon, The
2.5. Light microscopy
Semi-thin sections from the same embedded TEM sam-
ples were stained with toluidine blue and silver staining.
For a better evaluation of apoptotic nuclei, silver staining of
sections was also performed, by using a mixture of silver
nitrate (3m/ml) and hexamethylenetetramine (75g/ml).
3. Results
Turritopis nutricula was able to survive after different
types of stress, by a reorganization of adult tissues into a ju-
venile form. The most reproducible stress able to trigger life
cycle reversion was the exposure of the medusae to higher
temperatures (30C) than normal (22C). Under these con-
ditions, 80% of medusae activated life cycle reversion.
By means of stereoscopy observation, we identified four
easy to distinguish stages during the inverted life cycle
and we named them: healthy medusa, unhealthy medusa,
four-leaf clover and cyst. The light micrograph in Fig. 1
shows their very different macroscopic morphology.
Each stage had the following characteristics. The healthy
medusa had a bell-shaped umbrella with long tentacles and
swam actively (Fig. 2a). The unhealthy medusa was not able
to swim and maintained its tentacles in a retracted position;
the transparency typical of the normal healthy medusa was
lost (Fig. 3a). The four-leafed stage was characterized by the
E.C. Carla’ et al./Tissue & Cell 35 (2003) 213–222 215
Fig. 1. Life cycle of Turritopsis nutricula: (a) healthy medusa; (b) unhealthy medusa; (c) four-leaf clover; (d) cyst; (e) polyp. The double arrow indicates
the point of reversion of the cycle.
absence of tentacles, by the reduction of the sub-umbrella
cavity which showed a number of lobes and many degenera-
tive processes (Fig. 4a and b). The cyst stage had a spherical
shape and a smooth surface (Fig. 5a). It was able to attach
to the substrate and rapidly gave rise to a polyp morphologi-
cally similar to those generated during the normal life cycle.
By means of light, fluorescent, scanning and transmis-
sion electron microscopy the microscopic morphology of
the four stages was observed in order to analyze the mor-
phological modifications occurring at cellular level. In the
healthy medusa (Fig. 2), a large sub-umbrella cavity with a
central manubrium was observed (Fig. 2a and b). The um-
brella was delimited externally by an ectodermal layer, made
up of flat cells interconnected by tiny cytoplasmic protru-
sions (Fig. 2c, arrow). Mitochondria, glycogen droplets, and
rough and smooth endoplasmic reticula were abundant in
these cells. Epithelial muscle striated cells were detected as
well (Fig. 2d). The gonads and the gastric cavity in commu-
nication with the radial channels were recognized (Fig. 2e).
The ultrastructural investigation of the manubrium revealed
its highly complex organization, with many morphologically
different cytotypes: in particular, muscle cells with fibers ra-
dially oriented and glandular cells (Fig. 2f). Apoptotic cells
were also present in the manubrium (Fig. 2g and h).
In the unhealthy medusa (Fig. 3), the tentacles and
sub-umbrella cavity were reduced. The umbrella cells
showed many large empty vacuoles (Fig. 3c); many sarcom-
eres and mitochondria were still present in the epithelial
muscle cells, although a dramatic alteration of their mor-
phology was observed (Fig. 3d). Even more modifications
were revealed in the manubrium: cells lost cellular contacts
but maintained their junctional contacts (Fig. 3e, arrow-
head). The ectodermal cells had few cytoplasmic organelles;
endodermal cells were round; large electron dense vacuoles
were present in their cytoplasm (Fig. 3f). Some of these
cells showed clear signs of degeneration (Fig. 3g), probably
due to lytic phenomena, while other cells showed typical
features of apoptosis (Fig. 3h and i), However, the number
of apoptotic cells was lower than in the healthy medusa
(Table 1). Intracellular content and mesoglea were lost.
In the four-leaf clover stage (Fig. 4), the morphological
damage described for the unhealthy medusa became more
evident. Indeed, stress induced the total disappearance of
Table 1
Apoptosis and necrosis rate in the different stages of reverted life cycle
Stage Apoptosis (%) Necrosis (%)
Healthy +++ −−
Unhealthy +−+
Four-leaf clover ++++ −+
Cyst +++ ++
216 E.C. Carla’ et al./Tissue & Cell 35 (2003) 213–222
E.C. Carla’ et al./Tissue & Cell 35 (2003) 213–222 217
tentacles (Fig. 4a) and a further regression of the umbrella,
delimiting an irregular and more restricted sub-umbrella cav-
ity (Fig. 4b). Some of the umbrella cells had a round shape
and maintained cellular contacts (Fig. 4c), while other cells
were highly damaged showing many empty vacuoles in-
side the cytoplasm (Fig. 4d). The apoptotic rate was higher
growing (Fig. 4e and Table 1). Conversely, the muscle cells,
with radially oriented fibers (Fig. 4e, arrow), and the gonads
(Fig. 4f) were morphologically unchanged.
The medusae that lost all tentacles and the sub-umbrella
cavity that became spherical were defined cysts (Fig. 5).
Under SEM, this type showed a smooth and regular sur-
face (Fig. 5a). Light microscopy observation revealed a
two-layered spherical structure (Fig. 5b). The external cell
layer mainly consisted of two different cytotypes, which
were regularly distributed along the surface. In Fig. 5b,it
is possible to distinguish cells (probably gland cells “gc”,
mainly localized in the lower left part of the cyst) with
many fenestrae and a lesser quantity of small cytoplasmic
inclusions; cells rich in cytoplasmatic inclusions (probably
zymogenic cells, “zc”) were mainly concentrated in the
upper part of the cyst. The probable initial outline of the
stolon, seen as a protrusion of the left part of the cyst, is
shown in Fig. 5b (asterisk). In contrast, the internal layer
had a less regular organization and a great number of mor-
phologically different cells could be recognized. A specific
spatial distribution, probably related to the intense reorga-
nization of this stage, was observed for cells containing a
large number of zymogenic granules in the cytoplasm. The
cells surrounding the stolon’s outline are packed extremely
tightly. These cells are probably involved in the process
of stolon formation. The ultrastructural TEM investigation
showed that the cells of the external layer re-established
contacts (Fig. 5c and d) lost during the previous stages. The
fenestrate cells of the superficial layer are in contact with
each other and are divided from the inner cellular layer of
the cyst by compact and homogeneous substances, probably
mesoglea (Fig. 5c, mes). Interaction among cells was seen
to resume in the inner layer of the cyst, while isolated cells
could still be recognized in the cyst center (Fig. 5e). Many
of these cells showed condensed chromatin, as evidenced
by silver staining (Fig. 5f) and confirmed by TEM obser-
vation (Fig. 5g), thus indicating the presence of an intense
apoptotic rate. Gonads (Fig. 5i) were also present at this
stage as well as muscle tissue (Fig. 5h) in the cysts with
budding stolons.
By using FITC-conjugated lectins, we studied saccharide
residue exposure on T. nutricula cell surfaces during the
polyp, healthy medusa and unhealthy medusa stages. Sig-
Fig. 2. Healthy medusa. (a) Stereoscopic image of a medusa, showing the section plane of panel b; (b) semi-thin section of a medusa stained with
toluidine blue (magnification 20×); (c) umbrella cells with tiny touching protrusions (arrow) (magnification 6500×); (d) epithelial and muscle cells with
clearly visible sarcomeres (arrow) (magnification 7000×); (e) semi-thin section of manubrium showing gonads; (f) high magnification of gonads at E.M.
(magnification 5000×); (g) manubrium cells, “gl” a glandular cell, “mc” transversal section of muscle cell (magnification 3000×); (h) apoptotic cell (the
nucleus with condensed chromatin) inside the manubrium (magnification 5000×).
nificant differences between the healthy and the unhealthy
medusae were observed (Fig. 6). ConA, Ricinus communis
and Ulex binding sites were found in all the studied stages,
but differences in distribution and fluorescence intensity
were observed by a confocal microscope. Fluorescence was
quite intense in the gonads of unhealthy medusae while the
gonads of healthy medusae were labeled to a much lesser de-
gree. The cells lining the radial channels were also strongly
labeled and the labeling increased in the unhealthy medusae.
In the umbrella, the cells of healthy medusae showed faint
labeling with small scattered clusters of fluorescence. Con-
versely, the labeling increased in the unhealthy medusae as
did the number of fluorescent spots. The labeling observed
in the polyp was homogeneously distributed throughout the
tissues, with fluorescence intensity comparable to that of the
healthy medusa.
4. Discussion
The uncommon life cycle of T. nutricula involves the
transformation of an adult medusa to a polyp, which some
authors consider a juvenile stage (Boero et al., 1997). This
event represents a reverted development involving a crucial
process characterized by drastic modifications, comparable
to a sort of metamorphosis. During metamorphosis a large
part of the cell population acquires the fully differentiated
characteristics of adult cells (Truman, 1984; Weis and Buss,
1987). Furthermore, this process, occurring in many verte-
brate and invertebrate species, is often accompanied by de-
generative and apoptotic processes, well described for the
resorption of amphibian tail (Sanders and Wride, 1995).
Our ultrastructural study of cellular modifications during
the life cycle reversion of T. nutricula has shown the pres-
ence of both degenerative and apoptotic processes. Degen-
eration is prevalent during the stages of unhealthy medusa
and four-leaf clover, while apoptotic rate is high during the
stages of healthy medusa and cyst. The presence, even in the
healthy medusa, of apoptotic events is not surprising due to
its role in preserving cellular homeostasis in the majority of
animals (Wyllie et al., 1980; Gupta, 1996). Apoptosis also
plays an important role in many developmental processes,
such as cell differentiation, oogenesis (Sommer et al., 1998),
organogenesis, as well as in the establishment of body struc-
tures (Jacobson et al., 1997; Sanders and Wride, 1995). The
existence of apoptosis and its morphogenetic role during
body reorganization (from larva to polyp) of Hydractinia
echinata was first described by Seipp et al. (2001).InT.
nutricula’s reverted life cycle, the presence of degenerative
218 E.C. Carla’ et al./Tissue & Cell 35 (2003) 213–222
E.C. Carla’ et al./Tissue & Cell 35 (2003) 213–222 219
Fig. 4. (a) SEM micrograph of a four-leafed medusa showing the absence of tentacles (magnification 2000×); (b) stereoscopic image of a four-leafed
medusa; (c) round-shaped cells (magnification 3000×); (d) extensive vacuolization of ectodermal cells (magnification 2000×); (e) apoptotic cell (asterisk)
and radially sectioned muscle fibers (arrow) (magnification 3000×); (f) gonads (magnification 2000×).
Fig. 3. Unhealthy medusa. (a) Stereoscopic image of an unhealthy medusa; (b) SEM micrograph of an unhealthy medusa showing the retraction of
tentacles (magnification 2000×); (c) manubrium cells showing two cells that have began to detach (arrow) (magnification 4000×); (d) umbrella cells with
a damaged cytoplasm. An epithelial muscle cell shows a reduction of the striated fibers (arrows) (magnification 4500×); (e) ectodermal manubrium cells;
the cytoplasm has no intracellular organelles (magnification 5000×); (f) endodermal manubrium cells with cytoplasm rich in electron dense granules
(magnification 3500×); (g) endodermal manubrium cells. The cells are round and have lost contact with each other. Some show signs of necrosis (asterisk)
(magnification 5000×); (h) and (i) apoptotic cells inside the manubrium; h: initial stage of apoptosis with chromatin condensation and enlarged nuclear
cisternae (magnification 5000×); i: late/necrotic stage of apoptosis (magnification 6500×).
220 E.C. Carla’ et al./Tissue & Cell 35 (2003) 213–222
E.C. Carla’ et al./Tissue & Cell 35 (2003) 213–222 221
Fig. 6. Confocal images of Turritopsis nutricula (polyp, healthy and unhealthy medusa stages) sections labeled with fluorescent FITC-conjugated lectins.
as well as apoptotic processes supports our idea that this
inversion is a sort of metamorphosis, utilized to reorganize
body structure.
The cyst stage appears the most intriguing stage of the
entire reverted cycle of T. nutricula; this stage has a mor-
Fig. 5. (a) SEM micrograph of a cyst showing the almost smooth surface (magnification 3000×); (b) semi-thin section of a cyst. Two cellular layers are
shown. On the external layer the outline of the stolon is visible (see Section 3 for details) (magnification 1500×); (c) TEM micrograph of fenestrated cells
of the external layer. Mesoglea can be seen (mes) (magnification 3000×); (d) vacuolated and isolated cells of the central part of the cyst (magnification
2000×); (e) an apoptotic cell in secondary necrosis in the central part of the cyst (magnification 2000×); (f) silver methenamine staining of a cyst.
Many nuclei with condensed (apoptotic) chromatin are visible, in particular in the central region; (g) TEM micrograph of fenestrated cells of the external
layer with an intact and beam-shaped nucleus (magnification 2000×); (h) differentiated muscle cells with clearly visible sarcomeres in the part of the
cyst which is budding the stolon (magnification 2000×); (i) gonads (magnification 2000×).
phological organization similar to that of the planula larva:
cells are organized in two different layers. Therefore, it could
be hypothesized that cellular modifications (degeneration,
apoptosis and differentiation) during the cyst stage are simi-
lar to those characterizing the physiological metamorphosis
222 E.C. Carla’ et al./Tissue & Cell 35 (2003) 213–222
from planula to polyp; it follows that the cyst stage is not a
quiescent stage but more likely the most active one; indeed,
the high apoptotic rate could be a mechanism for cell selec-
tion, necessary for body reorganization and the development
of polyp tissues and structures.
Apoptotic process described in healthy medusae and in
the other stages, mainly cyst, may have different purposes.
In the healthy medusa, apoptosis is the normal process to
maintain cellular homeostasis; conversely in the cyst, apop-
tosis leads to dramatic body reorganization, a process similar
to what has previously been described for higher animals,
such as Drosophila (Jiang et al., 1997) or amphibians (Tata,
1993), in which apoptosis is used to remove typical larval
features, while simultaneously preserving those cells that
build up adult structures. Intriguing are the data concerning
the permanence of gonads throughout all stages. This rep-
resents clear evidence that both the young and the mature
medusa is able to revert its life cycle; further studies are
in progress to investigate their potential involvement in the
reconstruction of polyp structure.
Cellular morphological modifications that take place dur-
ing the reversion of the life cycle of T. nutricula underline,
of course, the various biochemical and molecular changes
affecting all compartments of the cell. This idea is supported
by the data obtained with a confocal microscope and re-
ported here concerning the analysis of the distribution of
lectin-binding sites. With this instrument many thin sections
through the sample were analyzed and very clean images
obtained by a virtual elimination of out-of-focus fluores-
cence, thus increasing clarity and contrast within the im-
ages (Diaspro, 2002). The high exposure of surface sugar
residues was observed in the unhealthy medusa, thus indicat-
ing that reorganization of the cell surface takes place during
this stage, most likely in order to abolish cellular contacts
and prepare the cellular reorganization of the cyst stage.
In conclusion, the presence of degenerative as well as
apoptotic processes, during the reverted life cycle of T. nu-
tricula have been shown. These morphological data support
the idea that when a medusa transforms itself into a polyp,
a sort of metamorphosis occurs.
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... The Mediterranean basin has a high rate of species endemism (28% of species are endemic), which may be predisposed to local extinction in such a fastchanging environment (Boero & Gravili 2013;Gravili et al. 2015a;Galli et al. 2017;García-Martínez et al. 2017). Several studies started focusing on the community and species repercussions of such warming tendency in this semi-closed area (Calvo et al. 2011;Goffredo & Dubinsky 2014). For example, studies of Lejeusne et al. (2010), focused on the effects of climate change on the Mediterranean biota, concluded that warming of water masses affects the marine ecosystems, being complex to distinguish the effects of the local anthropic activities from those due to natural events. ...
... In Hydrozoa genetic sex determination is a labile character and is characterized by a remarkable plasticity (Carré & Carré 2000) with tendency of reaching sexual maturity at early stages with increasing temperatures (Piraino et al. 1996;Carlà et al. 2003;Martell et al. 2016). Even bud development can be altered by sudden changes in temperature (see Berrill 1953 for Sarsia tubulosa (M. ...
... The description of ontogeny reversal (a medusa that metamorphoses into a hydroid) in Turritopsis dohrnii (Weismann, 1883) under environmental stress (Piraino et al. 1996(Piraino et al. , 2004Carlà et al. 2003;Martell et al. 2017) involves the contribution of trans-differentiation, I-cell-proliferation processes (Piraino et al. 1996), and the activation of celldeath programs (Carlà et al. 2003) confirming that development process must be considered "as an orchestration of both animal-encoded ontogeny and environmental interactions" (Bosch et al. 2014). ...
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Water temperature directly affects life cycles, reproductive periods, and metabolism of organisms living the oceans, especially in the surface zones. Due to the ocean warming, changes in water stratification and primary productivity are affecting trophic chains in sensitive world areas, such as the Mediterranean Sea. Benthic and pelagic cnidarians exhibit complex responses to climatic conditions. For example, the structure and phenology of the Mediterranean hydrozoan community displayed marked changes in species composition, bathymetric distribution, and reproductive timing over the last decades. The regional species pool remained stable in terms of species numbers but not in terms of species identity. When the Scyphozoa group is considered, we observe that Pelagia noctiluca (among the most abundant jellyfish in the Mediterranean Sea and eastern Atlantic waters) has increasingly frequent massive outbreaks associated to warmer winters. Variations in metabolic activities, such as respiration and excretion, are strongly temperature-dependent, with direct increment of energetic costs with jellyfish size and temperature, leading to growth rate reduction. Water temperature affects sexual reproduction through changes in the energy storage and gonad development cycles. Anthozoan life cycles depend also on primary productivity and temperature: gonadal production and spawning are tightly related in shallow populations (0-30 m depth) with the spring-summer temperature trends and autumn food availability. Overall, the energy transferred from the mother colonies to the offspring may decrease, negatively affecting their potential to settle, metamorphose and feed during the first months of their lives, eventually impairing the dominance of long-living cnidarian suspension feeders in shallow benthic habitats. In this review, we describe the already ongoing effects of sea warming on several features of cnidarian reproduction, trying to elucidate how reproductive traits and potential dispersion will be affected by the cascade effects of increasing temperature in the Mediterranean Sea.
... The PIWI-piRNA pathway effectively suppresses TE activity in the germline, but some specific somatic cells (eg, stem cells and tumor cells) have the ability to express PIWI genes and RNAs that interact with PIWI (Ross et al. 2014). Cnidarian, the jellyfish Turritopsis nutricula, is regarded as an "immortal" organism that is able to transform from an adult to a post-stage larval polyp and repeat this cycle indefinitely (Carla et al. 2003). Also, the H. vulgaris hydra body mainly consists of stem cell populations with unlimited ability to proliferate and self-renewal (Martinez 1998), which are characterized by high expression of PIWI proteins and PIWI-interacting RNAs (Watanabe et al. 2009;Juliano et al. 2014). ...
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Transposable elements exert a significant effect on the size and structure of eukaryotic genomes. Tc1/mariner superfamily elements represent the widely distributed and highly variable group of DNA transposons. Tc1/mariner elements include TLE/DD34-38E, MLE/DD34D, maT/DD37D, Visitor/DD41D, Guest/DD39D, mosquito/DD37E, and L18/DD37E families, all of which are well or less scarcely studied. However, more detailed research into the patterns of prevalence and diversity of Tc1/mariner transposons enables one to better understand the coevolution of the TEs and the eukaryotic genomes. We performed a detailed analysis of the maT/DD37D family in Cnidaria. The study of 77 genomic assemblies demonstrated that maT transposons are found in a limited number of cnidarian species belonging to classes Cubozoa (1 species), Hydrozoa (3 species) и Scyphozoa (5 species) only. The identified TEs were classified into 5 clades, with the representatives from Pelagiidae (class Scyphozoa) forming a separate clade of maT transposons, which has never been described previously. The potentially functional copies of maT transposons were identified in the hydrae. The phylogenetic analysis and the studies of distribution among the taxons and the evolutionary dynamics of the elements suggest that maT transposons of the cnidarians are the descendants of several independent invasion events occurring at different periods of time. We also established that the TEs of mosquito/DD37E family are found in Hydridae (class Hydrozoa) only. A comparison of maT and mosquito prevalence in two genomic assemblies of Hydra viridissima revealed obvious differences, thus demonstrating that each individual organism might carry a unique mobilome pattern. The results of the presented research make us better understand the diversity and evolution of Tc1/mariner transposons and their effect on the eukaryotic genomes.
... Pathways related to intercellular communication, such as those regulating apoptosis, are particularly relevant during head regeneration of H. vulgaris (23,24). Consistent with this, apoptosis has been reported in tissues from T. dohrnii during LCR (25). In this regard, we found gene amplifications associated with the neural system and apoptosis such as a duplication in PSEN1 (presenilin 1) in T. dohrnii compared to a single copy in T. rubra, as well as a notable expansion of BMP7 (bone morphogenetic protein 7), a gene with pleiotropic effects in modulation of apoptosis (26,27). ...
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Turritopsis dohrnii is the only metazoan able to rejuvenate repeatedly after its medusae reproduce, hinting at biological immortality and challenging our understanding of aging. We present and compare whole-genome assemblies of T. dohrnii and the nonimmortal Turritopsis rubra using automatic and manual annotations, together with the transcriptome of life cycle reversal (LCR) process of T. dohrnii. We have identified variants and expansions of genes associated with replication, DNA repair, telomere maintenance, redox environment, stem cell population, and intercellular communication. Moreover, we have found silencing of polycomb repressive complex 2 targets and activation of pluripotency targets during LCR, which points to these transcription factors as pluripotency inducers in T. dohrnii . Accordingly, we propose these factors as key elements in the ability of T. dohrnii to undergo rejuvenation.
... Elle fut surement surprise de constater que non seulement le greffon s'intégrait au sein de l'organisme hôte, mais qu'il induisait également un signal qui forçait les cellules environnantes à produire les tentacules (verts) autour de la bouche greffée (BROWNE 1909). Ces cellules vertes avaient déjà acquis une spécialisation cellulaire puisqu'elles composaient le corps de l'hydre hôte (figure 1B (PIRAINO et al. 1996;PAGLIARA et al. 2003;SCHMICH et al. 2007). ...
Les cellules différenciées peuvent être reprogrammées et adopter un destin cellulaire très différent. Connaître les acteurs et mécanismes qui contrôlent les processus de reprogrammation est un objectif scientifique fascinant qui éclairera notre compréhension du contrôle et du maintien de l'identité cellulaire. Notre laboratoire étudie le changement d'identité (ou transdifférenciation, TD) naturel d’une cellule épithéliale rectale (nommée Y) en motoneurone (nommé PDA) chez Caenorhabditis elegans. Dans les vers mutants pour le gène lin-15A (gène isolé dans un crible génétique du laboratoire), la cellule Y n'initie pas sa reprogrammation : Y demeure rectale. Cette protéine apparaît dans le noyau de Y juste avant le début de la TD de Y et joue un rôle clé dans l’initiation de ce processus. LIN-15A lie l’ADN et son domaine conservé en doigt de zinc (de type THAP-like) est essentiel pour initier la reprogrammation de Y. Nous nous sommes attachés à mieux comprendre le rôle de LIN-15A dans ce processus. L’inactivation de certains gènes (impliqués dans le maintien de l’identité cellulaire) permet de supprimer partiellement ou très fortement le défaut de reprogrammation de Y causé par la mutation lin-15A. Ces gènes appartiennent au groupe appelé synMuv B et ceux induisant la plus forte suppression du phénotype de lin-15A sont tous liés à la voie du rétinoblastome (RB). Dans la littérature, tous les mutants suppresseurs de défaut de PDA existant dans le mutant lin-15A présentaient une dérive de l’identité des cellules intestinales. Certains mutants de voies de réponse au jeûne chez le ver présentent également une perte du maintien de l’identité des cellules intestinales très similaire à celle induite par l’inactivation de certains gènes synMuv B. De façon très intéressante, nous avons pu observer que les vers mutants lin-15A présentent une pénétrance du défaut de PDA bien plus faible une fois privés de nourriture (au 1er stade larvaire ou au stade dauer). Certaines études laissent supposer que ces diapauses suite au jeûne entrainent une perte du maintien de l’identité cellulaire de cellules somatiques (et possiblement dans l’intestin), ce qui pourrait permettre à Y d’enclencher sa reprogrammation malgré l’absence de lin-15A, facteur clé à la levée du verrou pour initier la TD. En résumé, mes résultats ont montré que la transdifférenciation d'une cellule dépendait d'une clé moléculaire, LIN-15A, nécessaire pour lever un verrou de maintien de l'identité cellulaire dans la cellule qui va changer d'identité, et ce précisément juste avant la conversion cellulaire de Y en PDA. De façon plus générale, mes travaux ouvrent la possibilité que l'état physiologique et métabolique du ver influe sur le maintien de l'identité cellulaire. Sur le long terme, il conviendra alors de déterminer par quel biais cet état est perçu, dans quelles cellules, et comment cette information est relayée ou captée par la cellule Y, pour finalement influencer sa plasticité.
... The reverted lifecycle has been characterized by four different stages based on morphological analysis: healthy medusa, unhealthy medusa, four-leaf clover, and cyst. The four-leaf clover and unhealthy medusa stages were marked by degeneration while the healthy medusa and cyst stages were marked by a higher apoptotic rate (Carla et al., 2003). Compared to planarians, panther worms, and hydra, a lot less is known about this potentially immortal jellyfish. ...
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Radical lifespan disparities exist in the animal kingdom. While the ocean quahog can survive for half a millennium, the mayfly survives for less than 48 h. The evolutionary theories of aging seek to explain why such stark longevity differences exist and why a deleterious process like aging evolved. The classical mutation accumulation, antagonistic pleiotropy, and disposable soma theories predict that increased extrinsic mortality should select for the evolution of shorter lifespans and vice versa. Most experimental and comparative field studies conform to this prediction. Indeed, animals with extreme longevity (e.g., Greenland shark, bowhead whale, giant tortoise, vestimentiferan tubeworms) typically experience minimal predation. However, data from guppies, nematodes, and computational models show that increased extrinsic mortality can sometimes lead to longer evolved lifespans. The existence of theoretically immortal animals that experience extrinsic mortality - like planarian flatworms, panther worms, and hydra - further challenges classical assumptions. Octopuses pose another puzzle by exhibiting short lifespans and an uncanny intelligence, the latter of which is often associated with longevity and reduced extrinsic mortality. The evolutionary response to extrinsic mortality is likely dependent on multiple interacting factors in the organism, population, and ecology, including food availability, population density, reproductive cost, age-mortality interactions, and the mortality source.
Introdução: Por volta do século XIX uma descoberta sobre biologia marinha prometia mudar a percepção de imortalidade: desde os primórdios o que se entendia sobre imortalidade sempre foi relacionado às mitologias e religiões que descreviam algo ou alguém que nunca envelhecia. Entretanto, em meados do século XIX, notou-se a existência da Turritopsis dorhnii na classe dos hidrozoários por ter a capacidade de reverter seu ciclo de vida adulta (medusa) de volta ao inicial (pólipo), suspendendo assim a classificação de morte biológica, logo, ganhando o apelido de “água-viva imortal”. Objetivo: A proposta desta revisão é ressaltar a importância do estudo da epigenética deste hidrozoário, com foco em sua capacidade de transdiferenciação e desenvolvimento reverso, ambos claramente observados neste organismo, buscando através disso contribuir para estudos que objetivam compreender novas técnicas anti-senescência em outros organismos. Método: Este estudo constitui uma revisão bibliográfica. As bases de dados Literatura Latino-Americana e do Caribe em Ciências da Saúde (LILACS), Scientific Eletrônic Library Online (SCIELO) e National Library of Medicine (PUBMED). Foi definido como critério de inclusão: artigos publicados entre os anos de 1970 e 2020, os descritores utilizados foram: Transdiferenciação. Desenvolvimento reverso. Turritopsis dorhnii. Hidrozoários. Resultados: A análise dos trabalhos sobre a imortalidade da Turritopsis dorhnii contribuem para um melhor entendimento dos mecanismos que fazem com que esse organismo tenha a capacidade de transdiferenciação e desenvolvimento reverso, trazendo informações importantes para estudos dos mesmos mecanismos e que possam ser aplicados a outros organismos, inclusive no estudo de células humanas. Considerações finais: Concluímos que os estudos aqui reunidos a respeito da imortalidade biológica, são de grande contribuição, elucidando de forma cronológica as descobertas e apontando um direcionamento para os próximos estudos. Porém, fica evidente, a necessidade de estudos mais profundos no tema, principalmente na área molecular.
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Adult stem cells (ASCs) in vertebrates and model invertebrates (e.g. Drosophila melanogaster) are typically long-lived, lineage-restricted, clonogenic and quiescent cells with somatic descendants and tissue/organ-restricted activities. Such ASCs are mostly rare, morphologically undifferentiated, and undergo asymmetric cell division. Characterized by 'stemness' gene expression, they can regulate tissue/organ homeostasis, repair and regeneration. By contrast, analysis of other animal phyla shows that ASCs emerge at different life stages, present both differentiated and undifferentiated phenotypes, and may possess amoeboid movement. Usually pluri/totipotent, they may express germ-cell markers, but often lack germ-line sequestering, and typically do not reside in discrete niches. ASCs may constitute up to 40% of animal cells, and participate in a range of biological phenomena, from whole-body regeneration, dormancy, and agametic asexual reproduction, to indeterminate growth. They are considered legitimate units of selection. Conceptualizing this divergence, we present an alternative stemness metaphor to the Waddington landscape: the 'wobbling Penrose' landscape. Here, totipotent ASCs adopt ascending/descending courses of an 'Escherian stairwell', in a lifelong totipotency pathway. ASCs may also travel along lower stemness echelons to reach fully differentiated states. However, from any starting state, cells can change their stemness status, underscoring their dynamic cellular potencies. Thus, vertebrate ASCs may reflect just one metazoan ASC archetype.
The irreversible switch of one differentiated cell type to another is known as transdifferentiation. To consider that such cell‐type switching events arise through mistakes in normal development and tissue repair is a misnomer. It has long been accepted that many invertebrate organisms have the potential for transdifferentiation as part of their normal development or as a mechanism for replacing and regenerating lost or damaged tissue. Although their capacity for transdifferentiation is limited, this is also true for vertebrates and as such, several examples of naturally occurring, experimentally induced and disease‐related cell‐type interconversions have been described for higher organisms. These cell‐type conversions have important implications for understanding normal cell and tissue differentiation, the molecular and cellular basis of disease and may even facilitate the development of novel strategies for cell replacement and gene therapy in regenerative medicine. For a cell‐type conversion to be classified as transdifferentiation, two criteria have to be fulfilled (1) describe the loss of one cell phenotype and the gain of another and (2) demonstrate a direct ancestor–descendant relationship between the two cell types. Transdifferentiation is associated with a discrete change in the programme of gene expression. Transdifferentiation belongs to a broader group of cell type conversions called metaplasias. Metaplasia is derived from the Greek word ‘metaplassein’ meaning ‘to mould into a new form’ and was first used to define the unexpected appearance of foreign tissues in ectopic sites. Metaplasias also includes the conversion of one tissue‐specific stem cell to another tissue stem cell. Some invertebrates demonstrate a remarkable capacity for transdifferentiation as part of their regenerative response to cell or tissue damage. The potential for transdifferentiation in vertebrates is relatively limited compared to invertebrate organisms. During transdifferentiation, cells pass through an intermediate state that may be progenitor‐like or unspecific, the nature of these intermediates is poorly understood.
The quest for increased human longevity has been a goal of mankind throughout recorded history. Recent molecular studies are now providing potentially useful insights into the aging process which may help to achieve at least some aspects of this quest. This chapter will summarize the main findings of these studies with a focus on long-lived mutant mice and worms, and the longest living natural species including Galapagos giant tortoises, bowhead whales, Greenland sharks, quahog clams and the immortal jellyfish.
The Hydrozoa, an inconspicuous taxon of invertebrates, contributes significantly to the bulk of biodiversity but, usually, is noticed only by specialised taxonomists. The taxon Hydrozoa of the phylum Cnidaria comprises about 3800 nominal species, about which knowledge has greatly progressed in recent decades due to the scientific research of some specialists, particularly in the Mediterranean area. Past and present-day information on the global geographic distribution of hydrozoan species was analysed and compared to select those species that have shown fluctuations and geographic shifts in relation to warming of oceanic and marine waters and that can play a powerful and functional ‘sentinel-role’ of global warming. The growth of knowledge of the occurrence and distribution of hydrozoan species is attributable to the labours of numerous zoologists and naturalists, from the beginning of the eighteenth century onwards through many investigations at sea by geographical and oceanographic expeditions. Moreover, the expedition collections were frequently sent to different researchers who tended to specialise either in medusae or in hydroids. The defects of this dual system and large gaps in knowledge of relationships between medusae and hydroids have remained for a long time. Biogeography of the Hydrozoa is a broad field of inquiry combining different approaches, such as the evolutionary (biogeographical) and contemporary (ecological) ones. Nonetheless, numerous efforts have been made to bridge this gap and we are closer to a biogeographical synthesis than ever before. Therefore, initiatives to promote integration among disciplines should be encouraged to achieve a synthetic and comprehensive science of zoogeography.
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Organisms develop through a series of stages leading to sexually mature adults. In a few cases ontogeny reversal is possible, but it does not occur typically after the onset of sexual reproduction. Al1 stages of the medusa Turritopsis nutricula, from newly liberated to fully mature individuals, can transform back into colonia1 hydroids, either directly or through a resting period, thus escaping death and achieving potential immortality. This is the first metazoan known to revert to a colonial, juvenile morph after having achieved sexual rnaturity in a solitary stage. Selective excision experiments show that the trans-formation of medusae into polyps occurs only if differ-entiated cells of the exumbrellar epidermis and part of the gastrovascular system are present, revealing a trans-formation potential unparalleled in the anima1 kingdom.
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A gene, reaper (rpr), that appears to play a central control function for the initiation of programmed cell death (apoptosis) in Drosophila was identified. Virtually all programmed cell death that normally occurs during Drosophila embryogenesis was blocked in embryos homozygous for a small deletion that includes the reaper gene. Mutant embryos contained many extra cells and failed to hatch, but many other aspects of development appeared quite normal. Deletions that include reaper also protected embryos from apoptosis caused by x-irradiation and developmental defects. However, high doses of x-rays induced some apoptosis in mutant embryos, and the resulting corpses were phagocytosed by macrophages. These data suggest that the basic cell death program is intact although it was not activated in mutant embryos. The DNA encompassed by the deletion was cloned and the reaper gene was identified on the basis of the ability of cloned DNA to restore apoptosis to cell death defective embryos in germ line transformation experiments. The reaper gene appears to encode a small peptide that shows no homology to known proteins, and reaper messenger RNA is expressed in cells destined to undergo apoptosis.
The distribution of the 346 hydromedusan species hitherto recorded from the Mediterranean is considered, dividing the species into zoogeographical groups. The consequences for dispersal due to possession or lack of a medusa stage in the life cycle are discussed, and related to actual known distributions. There is contradictory evidence for an influence of life cycle patterns on species distribution. The Mediterranean hydromedusan fauna is composed of 19.5% endemic species. Their origin is debatable. The majority of the remaining Mediterranean species is present in the Atlantic, with various world distributions, and could have entered the Mediterranean from Gibraltar after the Messinian crisis. Only 8.0% of the fauna is classified as Indo-Pacific, the species being mainly restricted to the eastern basin, some of which have presumably migrated from the Red Sea via the Suez Canal, being then classifiable as Lessepsian migrants. The importance of historical and climatic factors in determining the composition of the Mediterranean fauna of hydromedusae is discussed.
The classification of cell death can be based on morphological or biochemical criteria or on the circumstances of its occurrence. Currently, irreversible structural alteration provides the only unequivocal evidence of death; biochemical indicators of cell death that are universally applicable have to be precisely defined and studies of cell function or of reproductive capacity do not necessarily differentiate between death and dormant states from which recovery may be possible. It has also proved feasible to categorize most if not all dying cells into one or the other of two discrete and distinctive patterns of morphological change, which have, generally, been found to occur under disparate but individually characteristic circumstances. One of these patterns is the swelling proceeding to rupture of plasma and organelle membranes and dissolution of organized structure—termed “coagulative necrosis.” It results from injury by agents, such as toxins and ischemia, affects cells in groups rather than singly, and evokes exudative inflammation when it develops in vivo. The other morphological pattern is characterized by condensation of the cell with maintenance of organelle integrity and the formation of surface protuberances that separate as membrane-bounded globules; in tissues, these are phagocytosed and digested by resident cells, there being no associated inflammation.
An argument is proposed to explain the origin of large metazoans, based on the regulatory processes that underlie the morphogenetic organization of pattern in modern animals. Genetic regulatory systems similar to those used in modern, indirectly developing marine invertebrates are considered to indicate the Precambrian regulatory platform on which were erected innovations that underlie the development of macroscopic body plans. Those systems are genetic regulatory programs that produce groups of unspecified "set-aside cells" and hierarchical regulatory programs that initially define regions of morphogenetic space in terms of domains of transcription factor expression. These ideas affect interpretation of the development of arthropods and chordates as well as interpretation of the role of the genes of the homeotic complex in embryogenesis.