No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Eye development and retinal differentiation in a betta splendens fish regan, 1909] "artigo científico/scientific article"
Abstract
The present study it aimed at to describe the ocular development, with emphasis in the retina of the Betta splendens fish, an ornamental fish that presents an extra-embryonic development, favoring research that involves one better agreement of its embryology and studies on degenerations and regenerations, ontogeny and differentiation occured in the eye, this research was carried through of the embryonic period up to ten days post-eclosão. The complete development of the eye when it has the eclosion of the animal. For the study of the stages of development the animals had been anesthetized in water with Eugenol 50ppm, were fixed in a solution of 4% paraformaldehyde in phosphate buffer, dehydrated and infiltrated with Paraplast Plus. After that, confectioned sections of 1-5μm of thickness and stained with HE, PAS and staining TUNEL. As result was possible to observe that the eyes had appeared of evaginações of diencéfalo, forming the optic cup. Neuroectoderm, the mesoderm and the ectoderm of the surface are involved in the formation of the eye. The staining TUNEL identified to process of apoptotic cells in the retina and lens, proving that it has a reduction of cells during the development of the animal. In the adult fish, through the chemistry it was possible to observe the morphology and the cellular arrangement of the photoreceptors.
... The retina of Betta splendens was formed (with seven layers) within 4 days and similar reports were observed on zebrafish (Danio rerio) (Gahtan et al., 2005) and catfish (Pangasianodon hypophthalmus) (Mukai et al., 2010). While, Oliveira and Sa (2012) have reported that the eye of B. splendens is strongly pigmented at hatching, other study claim that at this stage the eyes of B. splendens are undifferentiated and only slightly pigmented (Valentin et al., 2013). ...
Basic studies on early morphology and behaviour are necessary to support applied research on larval rearing. Thus, the aim of this study was to analyze the initial feeding behaviour, eye structure and the influence of different background colours (red, blue and clear) on prey capture rates (Artemia sp.) of Betta splendens larvae. The retina was formed by 90 h post-fertilization and consisted of seven layers. The feeding behaviour of the larvae changed with ocular development and thus, prey were captured more efficiently with time. No significant difference (p>0.05) was observed between the different background colours on prey capture rates under the experimental conditions tested (10 min of exposure). In conclusion, B. splendens larvae displayed a typical feeding behaviour, which changed with larval development and was dependent on visual ontogeny. Even though the different background colours did not significantly affect feeding behaviour, our findings provide important insights for future studies on this field.
Shallow-water zooplanktivorous fish rely on their vision for foraging. In shallow water, feeding efficiency decreases in dim light and thus the fish cease foraging at crepuscular hours. Creatures living in the lower parts of their depth ranges are expected to be exposed to limited light levels for longer hours. However, observations of the zooplanktivore Dascyllus marginatus showed little change in foraging duration down to 40m deep. We asked whether the visual system's functionality changes with depth along the depth range of this damselfish; we examined eye and retina anatomy for changes in visual acuity and light sensitivity and used the optomotor response to test for spatial and temporal light summation. We found only minor changes in the anatomy of the eye that are not expected to affect visual sensitivity or acuity. However, behavioural experiments showed that the deeper water fish's test performance exceeded those of fish in shallow water under lower light levels. We found that deeper water fish responded to the optomotor test at lower light levels and also had more discriminating visual acuity in low light, which can increase their potential reactive distance. The plastic adaptive ability of the visual system to low light levels may explain the fish's ability to inhabit deeper reef habitats and thus expand their depth range limits.
Dysfunction of the retinal pigment epithelium (RPE), its loss, or separation from the underlying neural retina results in severe photoreceptor degeneration. Pigment epithelium-derived factor (PEDF) is a glycoprotein with reported neuroprotective and differentiation properties that is secreted in abundance by RPE cells. The "pooling" of PEDF within the interphotoreceptor matrix places this molecule in a prime physical location to affect the underlying neural retina. The purpose of this study was to analyze the morphogenetic activity of PEDF in a model of photoreceptor dysmorphogenesis induced by removal of the RPE. Eyes were dissected from embryonic Xenopus laevis, and the RPE was removed before culturing in medium containing PEDF, PEDF plus anti-PEDF antibodies, or medium alone. Control retinas were maintained with an adherent RPE. Light and electron microscopic analysis was used to examine retinal ultrastructure. Opsin was localized immunocytochemically and quantified as an index of outer segment membranous material and photoreceptor protein expression. Removal of the RPE resulted in an aberrant assembly of photoreceptor outer segments, loss of fine subcellular ultrastructure in photoreceptors, and a reduction in opsin protein levels when compared with control retinas. The addition of PEDF prevented the dysmorphic photoreceptor changes induced by RPE removal. In particular, photoreceptor ultrastructure, outer segment membrane assembly, and steady-state levels of opsin were equivalent to control conditions. Anti-PEDF antibodies completely blocked the morphogenetic activity of PEDF. These results indicate that PEDF is able to mimic the supportive role of the RPE on photoreceptors during the final stages of retinal morphogenesis.
The retina of the adult teleost fish is an important model for studying persistent and injury-induced neurogenesis in the vertebrate central nervous system. All neurons, with the exception of rod photoreceptors, are continually appended to the extant retina from an annulus of progenitors at the margin. Rod photoreceptors, in contrast, are added to differentiated retina only from a lineage of progenitors dedicated to making rods. Further, when the retina is lesioned, the lineage that produces only rods ceases this activity and regenerates retinal neurons of all types. The progenitors that supply neurons at the retinal margin and rod photoreceptors and regenerated neurons in the mature tissue originate from multipotent stem cells. Recent data suggest that the growth-associated neurogenic activity in the retina is regulated as part of the growth hormone/insulin-like growth factor-I axis. This paper reviews recent evidence for the presence of stem cells in the teleost retina and the molecular regulation of neurogenesis and presents a consensus cellular model that describes persistent and injury-induced neurogenesis in the retinas of teleost fish.
In this review we present a synthesis on the potential of vertebrate eye tissue regeneration, such as lens and retina. Particular emphasis is given to two different strategies used for regeneration, transdifferentiation and stem cells. Similarities and differences between these two strategies are outlined and it is proposed that both strategies might follow common pathways. Furthermore, we elaborate on specific clinical applications as the outcome of regeneration-based research.
Located between vessels of the choriocapillaris and light-sensitive outer segments of the photoreceptors, the retinal pigment epithelium (RPE) closely interacts with photoreceptors in the maintenance of visual function. Increasing knowledge of the multiple functions performed by the RPE improved the understanding of many diseases leading to blindness. This review summarizes the current knowledge of RPE functions and describes how failure of these functions causes loss of visual function. Mutations in genes that are expressed in the RPE can lead to photoreceptor degeneration. On the other hand, mutations in genes expressed in photoreceptors can lead to degenerations of the RPE. Thus both tissues can be regarded as a functional unit where both interacting partners depend on each other.
The retina is part of the central nervous system (CNS) and the optic nerve is a central tract. They form as an extension of the diencephalon, and many features of their development and structure are common to other regions of the CNS. The retina is also structurally distinctive and the unique features of the embryology of the retina and eye are best understood in terms of that structure and of the structural relationships between the retina and the other tissues of the eye. This review begins, therefore, with a brief summary of the origins of the tissues of the eye (this section) and a consideration (next section) of the shared and distinctive features of the histogenesis of the retina.
In fish and amphibia, retinal stem cells located in the periphery of the retina, the ciliary marginal zone (CMZ), produce new neurons in the retina throughout life. In these species, the retina grows to keep pace with the enlarging body. When birds or mammals reach adult proportions, however, their retinas stop growing so there appears to be no need for such a proliferative area with stem cells. It is a surprise, therefore, that recent data suggest that a region similar to the CMZ of fish and amphibia exists in the postnatal chick and the adult mouse.(1–3)BioEssays 22:685–688, 2000. © 2000 John Wiley & Sons, Inc.
We describe the major events in the retinogenesis in an altricial fish species, the Senegalese sole. The major developmental events in the sole retina occurred early after hatching (posthatching day 0, P0). Thus, (1) plexiform layers became recognizable at P1. (2) Proliferative activity disappeared from the central retina at P1, and, as development progressed, became restricted to cells located in the circumferential germinal zone, and to sparse cells dispersed throughout the inner nuclear layer and the outer nuclear layer. (3) Apoptotic cells were sparsely observed, randomly localized in all three nuclear layers of the early posthatching retina from P0 to P4. (4) The first synaptic vesicles were detected at P0 in early postmitotic ganglion cells. However, their appearance in the plexiform layers was delayed until P2. (5) The neurochemical development of most major retinal cell classes occurred between P0 and P5. Thus, although Isl1 immunoreactive ganglion cells were the first to become postmitotic in the vitreal surface of the central retina at P0, the first glutamine synthetase-expressing Müller cells appeared in the central retina by P5. The onset of expression for other retinal markers, such as rod opsin, calretinin, parvalbumin, alpha-tyrosine hydroxylase, and alpha-protein kinase C, occurred between P2 and P4. Our results suggest that the most relevant processes involved in Senegalese sole retinogenesis occur during the prolarval and early larval stages (P0-P5). Furthermore, we conclude that altricial fish species may constitute a convenient model organism to address the relationship between the structural and functional development of sensory organs with the acquisition of behavioral repertoires. J. Exp. Zool. (Mol. Dev. Evol.) 314B, 2010. (c) 2010 Wiley-Liss, Inc.
To assess the role of the transcription factor Sox9 in cartilage formation we have compared the expression pattern of Sox9 and Col2a1 at various stages of mouse embryonic development. Expression of Col2a1 colocalized with expression of Sox9 in all chondroprogenitor cells. In the sclerotomal compartment of somites the onset of Sox9 expression preceded that of Col2a1. A perfect correlation was also seen between high levels of Sox9 expression and high levels of Col2a1 expression in chondrocytic cells. However, no Sox9 expression was detected in hypertrophic chondrocytes; only low levels of Col2a1 RNA were found in the upper hypertrophic zone. Coexpression of Sox9 and Col2a1 was also seen in the notochord. At E11.5 Sox9 expression in the brain and spinal neural tube was more widespread than that of Col2a1 although at E14.5 Sox9 and Col2a1 transcripts were colocalized in discrete areas of the brain. Distinct differences between Sox9 and Col2a1 expression were observed in the otic vesicle at E11.5. At E8.5, expression of Sox9 but not of Col2a1 was seen in the dorsal tips of the neural folds and after neural tube closure also in presumptive crest cells emigrating from the dorsal pole of the neural tube. No Col2a1 expression was detected in gonadal ridges in which high levels of Sox9 expression were detected. Together with our previous results showing that the chondrocyte-specific enhancer element of the Col2a1 gene is a direct target for Sox9, these results suggest that Sox9 plays a major role in expression of Col2a1. The correlation between high expression levels of Sox9 and high expression levels of Col2a1 in chondrocytes suggests the hypothesis that high levels of Sox9 are needed for full expression of the chondrocyte phenotype; lower levels of Sox9 such as in neuronal tissues which are also associated with lower expression levels of Col2a1 would be compatible with other cell specifications.
The hedgehog (hh) genes encode secreted signaling proteins that have important developmental functions in vertebrates and invertebrates. In Drosophila, expression of hh coordinates retinal development by propagating a wave of photoreceptor differentiation across the eye primordium. Here we report that two vertebrate hh genes, sonic hedgehog (shh) and tiggy-winkle hedgehog (twhh), may perform similar functions in the developing zebrafish. Both shh and twhh are expressed in the embryonic zebrafish retinal pigmented epithelium (RPE), initially in a discrete ventral patch which then expands outward in advance of an expanding wave of photoreceptor recruitment in the subjacent neural retina. A gene encoding a receptor for the hedgehog protein, ptc-2, is expressed by retinal neuroepithelial cells. Injection of a cocktail of antisense (alphashh/alphatwhh) oligonucleotides reduces expression of both hh genes in the RPE and slows or arrests the progression of rod and cone photoreceptor differentiation. Zebrafish strains known to have mutations in Hh signaling pathway genes similarly exhibit retardation of photoreceptor differentiation. We propose that hedgehog genes may play a role in propagating photoreceptor differentiation across the developing eye of the zebrafish.
The programmed degradation of organelles is a characteristic feature of lens fibre cell differentiation. Due to the large number of similarities between the programmed organelle loss during lens development and the changes to organelles in apoptosis, lens cell differentiation has been suggested to share a common basis with programmed cell death. This study was aimed at characterising the morphological changes to the nucleus during cellular differentiation in the bovine lens at the ultrastructural level. Progressive shrinkage of the nucleus is accompanied by clumping and marginalisation of the chromatin to the nuclear periphery. Additionally, the fate of another key component of the nuclear envelope--the nuclear pore complexes--was followed. In parallel to the shrinkage of the nucleus, the nuclear pores progressively cluster into large aggregates that associate with the condensed DNA. These observations in differentiating lens fibres mirror the situation in cells undergoing apoptosis and thus provide additional data supporting a common basis between the two processes.
The zebrafish has become an important vertebrate model organism to study the development of the visual system. Mutagenesis projects have resulted in the identification of hundreds of eye mutants. Analysis of the phenotypes of these mutants relies on in depth knowledge of the embryogenesis in wild-type animals. While the morphological events leading to the formation of the retina and its connections to the central nervous system have been described in great detail, the characterization of the development of the eye lens is still incomplete. In the present study, we provide a morphological description of embryonic and larval lens development as well as adult lens morphology in the zebrafish. Our analyses show that, in contrast to other vertebrate species, the zebrafish lens delaminates from the surface ectoderm as a solid cluster of cells. Detachment of the prospective lens from the surface ectoderm is facilitated by apoptosis. Primary fibre cell elongation occurs in a circular fashion resulting in an embryonic lens nucleus with concentric shells of fibres. After formation of a monolayer of lens epithelial cells, differentiation and elongation of secondary lens fibres result in a final lens morphology similar to that of other vertebrate species. As in other vertebrates, secondary fibre cell differentiation includes the programmed degradation of nuclei, the interconnection of adjacent fibres via protrusions at the fibre cells' edges and the establishment of gap junctions between lens fibre cells. The very close spacing of the nuclei of the differentiating secondary fibres in a narrow zone close to the equatorial epithelium, however, suggests that secondary fibre cell differentiation deviates from that described for mammalian or avian lenses. In summary, while there are similarities in the development and final morphology of the zebrafish lens with mammalian and avian lenses, there are also significant differences, suggesting caution when extrapolating findings on the zebrafish to, for example, human lens development or function.