Fertilization in the medusan, Spirocodon saltatrix.
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ABSTRACT: Jellyfish eggs neither undergo apparent cortical reaction nor show any significant change in the membrane potential at fertilization, but nevertheless show monospermy. Utilizing the perfectly transparent eggs of the hydrozoan jellyfish Cytaeis uchidae, here we show that the polyspermy block is accomplished via a novel mechanism: a collaboration between Ca(2+) and mitogen-activated protein kinase (MAPK). In Cytaeis, adhesion of a sperm to the animal pole surface of an egg was immediately followed by sperm-egg fusion and initiation of an intracellular Ca(2+) rise from this site. The elevated Ca(2+) levels lasted for several minutes following the sperm-egg fusion. The Ca(2+) rise proved to be necessary and sufficient for a polyspermy block, as inhibiting a Ca(2+) rise with EGTA promoted polyspermy, and conversely, triggering a Ca(2+) rise by inositol 1,4,5-trisphosphate (IP3) or excess K(+) immediately abolished the egg's capacity for sperm-egg fusion. A Ca(2+) rise at fertilization or by artificial stimulations evoked dephosphorylation of MAPK in eggs. The eggs in which phosphorylated MAPK was maintained by injection of mRNA for MAPK kinase kinase (Mos), like intact eggs, exhibited a Ca(2+) rise at fertilization or by IP3 injection, and shut down the subsequent sperm-egg fusion. However, the Mos-expressing eggs became capable of accepting sperm following the arrest of Ca(2+) rise. In contrast, addition of inhibitors of MAPK kinase (MEK) to unfertilized eggs caused MAPK dephosphorylation without elevating Ca(2+) levels, and prevented sperm-egg fusion. Rephosphorylation of MAPK by injecting Mos mRNA after fertilization recovered sperm attraction, which is known to be another MAPK-dependent event, but did not permit subsequent sperm-egg fusion. Thus, it is possible that MAPK dephosphorylation irreversibly blocks sperm-egg fusion and reversibly suppresses sperm attraction. Collectively, our data suggest that both the fast and late mechanisms dependent on Ca(2+) and MAPK, respectively, ensure a polyspermy block in jellyfish eggs.Developmental Biology 05/2014; · 3.87 Impact Factor
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ABSTRACT: Gamete age has been postulated to be unimportant to the fertilization ecology of marine invertebrates. However, recent research suggests that, for some species at least, it may have a direct impact upon fertilization success. We present comparative data on the influence of gamete age on fertilization and development success in several marine invertebrates: the polychaetes Arenicola marina and Nereis virens and the asteroid echinoderm Asterias rubens. Oocytes are much longer lived in the polychaetes than in the echinoderm, with A. marina oocytes still capable of fertilizing and developing normally 96 h post-spawning. Developmental abnormalities and failure to reach blastula tend to occur well before the fertilizable life of the oocytes has expired. Sperm are similarly longer lived in the polychaetes; however, fertilizing capacity is markedly reduced following incubation in conspecific egg-conditioned seawater. These results are discussed in terms of the fertilization strategies of the three species. We further suggest that, for A. marina at least, longer-lived sperm and eggs are central to the fertilization strategy of this species.Biological Bulletin 03/2002; 202(1):34-42. · 1.23 Impact Factor
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ABSTRACT: Egg extracts from 32 species of marine hydromedusae, siphonophores and sessile hydroids were tested for sperm attracting activity using the sperm of all species in both homo- and heterospecific combinations. Species-specific sperm chemotaxis could be demonstrated in nearly every species tested. Of the 1,024 possible combinations, 272 could not be attempted for lack of material. Of the 752 which were carried out, only 13 heterospecific cross-reactions were found. The bulk of these involved reactions which were either weaker in the heterospecific direction or unidirectional. The sperm behavior in response to both homospecific and heterospecific egg extracts is described. In the latter case, no changes in sperm motility or direction of movement were observed. In the former case, the sperm show turning behavior which brings them closer to the source of the extract. Since most of the Hydrozoa tested share the same habitat and are reproductively active at the same time of year, it appears that species-specific sperm chemotaxis may be a significant mechanism for both ensuring fertilization in an environment which subjects the gametes to massive dilution and preventing hybridization.Marine Biology 01/1979; 53(2):99-113. · 2.39 Impact Factor
JEAN C. DAN
Tokyo MetropolitanU@:ivcrsity and Misaki@1'Iarinc Biological Station
tween four and eight centimeters
of the deeper bays
January. Theyoungadultscarryfullydeveloped eggsandspermfromthetime
of their first appearance,and during the succeeding
constantly,graduallyincreasingin size and shifting
the bays towardthe open sea. At the middle of March most of the animals
are at the upperlimit of the size range amid contain
sperm.There is a brief period during which the gametes are obviously
mal condition,after which the medusaecompletely
the Station.Nothinghas as yet been learned
species during the remainingnine months of the year.
The embryologyof S. saltatrixhas not been investigated
so far to rear larvae past the gastrulastage or to collect intermediate
methodof inducingspawningwas developed
the darkin the laboratorycausesa copious
matelyan hour, regardlessof theday-night
a previousexposureof ten to fifteen minutes
improvesthe reactivityto the stimulusof darkness.
Examinationof eggs taken from the ovaries during
noon reveals only immatureeggs, whereas spawned eggs are always fully mature.
is thus apparentthat the light-darkness change is the stimulus
the maturationdivisions,and eggs removed
been so stimulatedgo throughthe maturation
All attemptsto fertilizesuch eggs by adding
however,so farfailed,as havemethods
cut from animals just before spawningtime.
fertilizablefor only a very shorttime after
though the specific reason for this has not yet been determined.
In orderto obtaineggsin theearliest
were placed in sea water in separatecontainers
males invariablyspawnfirst, it was possible
outundue handlingof theanimals.)Females
placed either in a containerwith a shedding
shed sperm,andwatchedfor thebeginning
alsolosetheirfertilizing capacity aftera very
saltatrix,a bell-shapedmemberof the
in the inner waters
the animals breed
from the heads of
large quantities of eggs and
not in opti
from the waters
because of the failure
to the direct rays of an ordinary
the morningand early after
offor the beginning
of females which have
on the microscope
shed sperm to them have,
to â€œ¿?dryâ€•eggs shed from ovaries
It is thus obvious
theirexpulsionfrom the ovaries,
from the ovaries
that the eggs are
male or in sea water containing
the sexes with
sea water into which the eggs are to be shed.
container, a sample was removed
animal pole, where the polar bodies have just been extruded,
the pronucleuslies in contact with the egg surface.
may sometimesbe found still adhering
ally lost in the course of shedding
Thereare no envelopinglayers or membranes,
before or after fertilization.
care niust be exercisedto ensure the presenceof freshly shed sperm in the
As soon as eggs were observed
to a slide and observed
with the phase contrast
eggs(Fig.1) are slightly ovalwith
and at the base of which
One or both of the polar bodies
to the polar region, although
and the handlingof the eggs prior to observation.
so far as can be determined,
a depressionat the
these are usu
base of a slight
depressionthe extrusionof the secondbody.
of the egg pronucleus.
found in the fact that excess
eggs, even in the case of eggs which have been rendered
with sea water before the addition
Immediatelyafter the penetration
develops, aroundthe sperm tail, a tubular
creasesin both length and diameter
sperm tail, which maintainsslight but continuous
into the egg. The walls of this â€œ¿?fertilization tubeâ€•are entirely
spermtail is perfectly visible moving
second spermatozoanwas found with its head well within the tube.
courseof degeneration,duringwhich it continues
parently,any incrementin material.
tion of the structure,as thoughsea water were an unfavorable
istence. Breaks appearin the walls, and the lashing
animal pole of the egg,theirmovements
structure from its place of attachment,
tenuated, althoughfragmentsof its can sometimes
Completeengulfmentof the tail usually
is occurring,the egg becomes spherical,
appears.The egg pronucleus slowly leaves its original
surface, moving a short distance toward the center of the egg and showing a marked
evidence for the existence
for the free-swimming
sperm are found only around
enters the egg in the immediatevicinity
Furtherof some sort of specific
the animal pole of mature
on the part of the egg pronucleusis
of sperm suspension.
of the sperm head into the egg cortex,
for about five minutes
2a) which gradually
is steadily being drawn
the tube. In several
cases a freelywithin
the size shownin Figure
2e, the tube begins
in size without,
In fact, there seems to be a chemical dissolu
medium for its ex
of the shortening
if there are other spermatozoa
and it gradually
be found after 20â€”30minutes.
requiresabout 15 minutes.
and the indentation
becomes more and more at
at the animal pole dis
FERTILIZATIONIN SPIROCODON SALTATRIX415
tion of the cleavage pattern,
eggs failed to reveal any trace of the sperm head after it entered
safe to conjecturethatthe union
activity, between10 and 14 minutes
would accountfor the increasein nuclear
afterthe stage shownin Figure
to be followedshortlyby the appearance
positionpreviouslyoccupied by the fusion nucleus.
Althoughthe most careful observation of these remarkablytrans
the egg, it
of the sperm pronucleushas occurred,
after the beginning
2n, the outline
of the cleavage
of the nucleus disappears
For a descrip
is made to Dan and Dan, 1947.
Eggsof the tubularioanthomedusan,
In the mature
of a slight depression
spawnedinto sea water containing
fertilizingsperm always enters in the immediate
the sperm entrancepoint a tubular
velop aroundthe sperm
egg. Thiscontinuesto increase
after which a process of degeneration
the tube has become balloon-shaped
tip of the sperm tail is finally drawn into the egg.
The egg pronucleusmoves a short distance from the periphery
of the egg.A markedincrease
ning of fertilizationprobably indicates
althoughno astral activityis detectable.
of the maturation
at the completion
can in the
eggs, the pronucleus
at the animal
lies in contact with the surface,
pole.These eggs are fertilizable
freshly shed spermatozoa.
of such eggs with the phase contrast
at the base
microscopeshows that the
vicinity of the egg pronucleus.
structure begins to de
for aboutfive minutes,
tail as soon as the head of the sperm
and is more or less rapidly disintegrating,
At the end of about fifteen minutes
toward the center
after the begin in size between10 and 14 minutes
the union@of the sperm and egg pronuclei,
DAN, K., ANDJ. C. DAN, 1947. Behavior of the cell surface during cleavage.
cleavage of Medusan eggs.Biol. Bull., 93: 163â€”188.
KUME, M.,1948.Ovulation and related
Breeding, 9: 270â€”271.
UCHIDA, T.,1927.Studieson Japanese
Tokyo Imp. Univ. Ser. IV, 1: 145â€”242.
phenomenain Spirocodon saltatrix. Collecting and
hydromedusae.I. Anthomedusae. Jour.Fac.Sci.,
from beginning of observation.)
sperm tail gradually being drawn into egg.
disappearanceof polar depression.
Increase in size probably indicates fusion of egg and sperm pronuclei. Sperm tail completely
drawn intoegg, remnantof fertilization tube
(f) Beginning of degeneration
of sperm head.
to move inward.
lost. (n) Typicallyspherical conditionof