Inductive effect of the eye tissues of adult clawed toads on the gastrula ectoderm

The inducing influence of adult eye tissues on the early gastrula ectoderm was studied in vitro. Both retina and pigment epithelium induced in the early gastrula ectoderm similar spectra of cell types, including nervous tissue, retina, pigment epithelium, lentoids, ectomesenchyme, and melanophores. It is suggested that the correspondence of these cell types with those arising at a spontaneous transdifferentiation of the isolated retina and pigment epithelium cells in vitro or at the induction of the early gastrula ectoderma by archencephalic endomesoderm during the normal development can be accounted for by that in these eye cells molecular determinants appeared as a result of induction and maintaina the stability of their differentiation and their potencies to transdifferentiation in vitro being reproduced during the lifetime of these cells.     

Electrophoretic study of water-soluble retinal proteins of chickens at early stages of embryogenesis]

The water-soluble proteins of chick retina were studied during the formation of eye cup and at the early stages of histological differentiation of retina by the micro-method of electrophoresis in 20% polyacrilamide gel. The retina of embryos at the stages under study contains a range of proteins forming over 20 fractions in electrophoresis. The most fractions are formed by the proteins which electrophoretic mobilities exceed that of serum albumin. The early stages of retina development are characterized by the definite changes in its protein composition. These changes manifest themselves in the disappearance of the most anodic fractions beginning from the stage of contact between the optic vesicle and presumptive lens ectoderm. During the subsequent development, these proteins are detected again in the retina, the corresponding anodic fractions being most distinct at the stage of completed eye cup. Their content in the retina decreases repeatedly with the beginning of histogenesis up to their complete disappearance.     

Development and pathology of the hyaloid, choroidal and retinal vasculature

During embryogenesis, the development and differentiation of the eye requires the concomitant formation of the neural/glial elements along with a dense vascular network. The adult neural retina is supported by two distinct vascular systems, the proper retinal vessels and the choroidal vessels. The two beds differ not only in their pattern of embryonic differentiation, but also in their function in the adult organism. The retinal vasculature has barrier properties similar to those observed in the brain, whereas the choroidal vessels display a highly fenestrated phenotype. The hyaloid vasculature is a transient embryonic vascular bed which is complete at birth in mammals and regresses contemporaneously with the formation of the retinal vasculature. The dependence of the retina on its blood supply makes it highly vulnerable to any vascular changes and indeed ocular diseases, such as proliferative retinopathy, age-related macular degeneration and the hyperplastic primary vitreous, which are associated with abnormalities of the different vascular beds of the eye. A number of factors have been implicated in developmental and pathological changes in vessel formation and regression, including fibroblast growth factors, platelet-derived endothelial growth factor and vascular endothelial growth factor, among others. The purpose of this review is to describe and discuss new insights into the mechanisms and molecular cues involved in the development of the normal and pathological vascular systems of the eye. The characterization of the molecules and cell-cell interactions involved in the formation, stabilization and regression of new vessels has led to the identification of potential control points for therapeutic intervention.     

The effect of manipulating ecdysteroid signaling on embryonic eye development in the locust<Emphasis Type="Italic"> Schistocerca americana</Emphasis>

Adult body plan differentiation in holometabolous insects depends on global induction and control by ecdysteroid hormones during the final phase of postembryogenesis. Studies in Drosophila melanogaster and Manduca sexta have shown that this pertains also to the development of the compound eye retina. It is unclear whether the hormonal control of postembryonic eye development in holometabolous insects represents evolutionary novelty or heritage from hemimetabolous insects, which develop compound eyes during embryogenesis. We therefore investigated the effect of manipulating ecdysteroid signaling in cultured embryonic eye primordia of the American desert locust Schistocerca americana, in which ecdysteroid level changes are known to induce three rounds of embryonic molt. Although at a considerably reduced rate compared to in vivo development, early differentiation and terminal maturation of the embryonic retina was observed in culture even if challenged with the ecdysteroid antagonist cucurbitacin B. Supplementing cultures with 20-hydroxyecdysone (20E) accelerated differentiation and maturation, and enhanced cell proliferation. Considering these results, and the relation between retina differentiation and ecdysteroid level changes during locust embryogenesis, we conclude that ecdysteroids are not an essential but possibly a modulatory component of embryonic retina development in S. americana. We furthermore found evidence that 20E initiated precocious epithelial morphogenesis of the posterior retinal margin indicating a more general role of ecdysteroids in insect embryogenesis.Electronic Supplementary Material Supplementary material is available in the online version of this article at Edited by C. Desplan     

Regeneration of the retina in the adult newt, Triturus cristatus, following surgical division of the eye by a limbal incision.

The regeneration of a retina in adult Triturus cristatus, following surgical division of the eye by a limbal incision, was studied. In agreement with recent reports, it was found that the regenerating retina is dervied from two sources; the retinal pigment epithelium and the pars ciliaris retinae. However, following a limbal incision, most of the retina appears to be derived from the retinal pigment epithelium in the posterior part of the eye. An unexpected finding of this study was that large cystlike spaces form in the fundal regions of the eye, between the regenerating retina and the retinalpigment epithelium. These spaces appear between five and eight days post-operative and persist long enough (25 to 30 days postoperative) to disrupt the fundal portion of the rengenerating retina and to cause it to lag behind the rest of the regenerate, in its development. The relationship of these observations to the genesis of positional markers in the regenerating retina is discussed.     

Fine structure and development of the retina of the grenadier anchovy Coilia nasus (Engraulididae, Clupeiformes)

A study of the morphogenesis of the grenadier anchovy retina was undertaken using light and electron microscopy. Five developmental stages from prelarvae 3 days after fertilization to adult fish were studied. In addition to the general morphology of the eye and retina, special emphasis was given to the development of the photoreceptors and pigment epithelium (PE). The earliest retinae showing structural features indicative of a functioning eye are pure cone retinae composed of rows of alternating long and short cones forming a transient, tesselated pattern. At this stage there is a conventional PE containing melanin. In older stages cone rows are separated by the newly formed rods and by PE wedges filled with diffusely reflecting guanine crystallites. The findings are compared with the retinae of other engraulidids and with the development of teleost retinae in general. Moreover, the observed structural changes are discussed with respect to the photic habitat conditions of these anadromous fish that move between coastal waters, estuary, and river.     

Organotypic culture of neural retina as a research model of neurodegeneration of ganglion cells

Organotypic models deserve special attention among the large variety of methods of vertebrate retina cultivation. The purpose of this study was to make a detailed qualitative and quantitative characterization of a model employing roller organotypic cultivation of the neural retina of rat eye posterior segment, with special attention to morphological and functional characteristics of retinal ganglion cells. The study included morphological analysis of retina histological preparations as well as estimation of RNA synthesis and evaluation of neuron survival by the Brachet and TUNEL methods, respectively. Retina has been shown to display normal morphofunctional characteristics for the first 12 h of cultivation. After 24 h, a substantial number of ganglion cells underwent pyknosis and stopped RNA synthesis. Almost all the cells of the retinal ganglion layer became apoptotic by 3–4 days in vitro. In the course of cultivation, neural retina is detached from the underlying layers of the posterior eye segment and undergoes significant cytoarchitectonic changes. The causes of ganglion cell death during organotypic cultivation of eye posterior segment are discussed. This method can serve as a suitable model for the screening of new retinoprotectors and for research on ganglion cell death resulting from retina degenerative diseases, e.g. glaucoma.     

Retinoids, eye development, and maturation of visual function

Vitamin A is known to be critical for the beginning of eye development as well as for photoreception in the functional retina. Hardly anything, however, is known about whether retinoic acid (RA)-regulated gene expression also plays a role in the long intervening period, during which the neurobiological retinal structure takes shape. The eye contains a highly intricate architecture of RA-synthesizing (RALDH) and degrading (CYP26) enzymes. Whereas the RALDHs are integrated in the early molecular mechanisms through which the dorso-ventral retina organization is established, the CYP26 enzymes are not necessary for this process and no molecular targets that match their retinal expression pattern have yet been identified. In this article we describe that CYP26 expression in the mouse is most distinctive during later stages of retina formation. Throughout development CYP26A1 degrades RA in a horizontal region that extends across the retina, but during later embryonic and postnatal retina maturation this function is reinforced by another enzyme, CYP26C1. RA applications at this stage do not affect the RALDHs but cause differential changes in CYP26 expression: Cyp26a1 is up-regulated, but more rapidly by 9-cis than all-trans RA, Cyp26c1 is down-regulated, and Cyp26b1, which is undetectable in the normal mouse retina, is strongly activated in retinal ganglion cells. The dynamic regulation in RA-difference patterns by the CYP26 enzymes may set up spatial constellations for expression of genes involved in formation of retinal specializations for higher acuity vision, which are known to form over a prolonged period late in retina development.     

Use of pIRES vectors to express EGFP and connexin constructs in studies of the role of gap junctional communication in the early development of the chick retina and brain

Control of cell proliferation is vital for the normal development of the neural retina. Gap junctional communication has been implicated in the control of retinal cell proliferation. We have previously shown that the expression of the gap junction protein Connexin 43 closely correlates with the first wave of cell proliferation in the retina. Preventing its expression using antisense oligonucleotides in the developing eye and surrounding tissues, produces a reduction in cell number and the formation of a small eye. In order to examine this in more detail we have developed a new means of manipulating connexin expression in the developing chick embryo. We have generated pIRES vectors which use cyclomegalovirus (CMV) to promote the expression of a green fluorescent protein (EGFP) and either wild type Cx43 or a dominant negative form ofthis connexin. Following injection ofthese constructs into the ventricles ofthe stage 10-11 chick embryo they can be incorporated into one side of the chick brain or optic vesicle using an electroporation technique, leaving the other side as a control. EGFP expression can be seen on the electroporated side of the chick brain within 24 hours. Expression of the dominant negative construct in cultures of chick limb bud mesenchyme results in total block of cascade blue transfer when injected into transfected cells. Expression of both wild type and dominant negative constructs in the developing chick retina perturbs the normal development of the eye.     

The temporal requirement for vitamin A in the developing eye: mechanism of action in optic fissure closure and new roles for the vitamin in regulating cell proliferation and adhesion in the embryonic retina

Mammalian eye development requires vitamin A (retinol, ROL). The role of vitamin A at specific times during eye development was studied in rat fetuses made vitamin A deficient (VAD) after embryonic day (E) 10.5 (late VAD). The optic fissure does not close in late VAD embryos, and severe folding and collapse of the retina is observed at E18.5. Pitx2, a gene required for normal optic fissure closure, is dramatically downregulated in the periocular mesenchyme in late VAD embryos, and dissolution of the basal lamina does not occur at the optic fissure margin. The addition of ROL to late VAD embryos by E12.5 restores Pitx2 expression, supports dissolution of the basal lamina, and prevents coloboma, whereas supplementation at E13.5 does not. Surprisingly, ROL given as late as E13.5 completely prevents folding of the retina despite the presence of an open fetal fissure, showing that coloboma and retinal folding represent distinct VAD-dependent defects. Retinal folding due to VAD is preceded by an overall reduction in the percentage of cyclin D1 positive cells in the developing retina, (initially resulting in retinal thinning), as well as a dramatic reduction in the cell adhesion-related molecules, N-cadherin and β-catenin. Reduction of retinal cell number combined with a loss of the normal cell-cell adhesion proteins may contribute to the collapse and folding of the retina that occurs in late VAD fetuses.     

Use of pIRES Vectors to Express EGFP and Connexin Constructs in Studies of the Role of Gap Junctional Communication in the Early Development of the Chick Retina and Brain

Control of cell proliferation is vital for the normal development of the neural retina. Gap junctional communication has been implicated in the control of retinal cell proliferation. We have previously shown that the expression of the gap junction protein Connexin 43 closely correlates with the first wave of cell proliferation in the retina. Preventing its expression using antisense oligonucleotides in the developing eye and surrounding tissues, produces a reduction in cell number and the formation of a small eye. In order to examine this in more detail we have developed a new means of manipulating connexin expression in the developing chick embryo. We have generated pIRES vectors which use cyclomegalovirus (CMV) to promote the expression of a green fluorescent protein (EGFP) and either wild type Cx43 or a dominant negative form of this connexin. Following injection of these constructs into the ventricles of the stage 10-11 chick embryo they can be incorporated into one side of the chick brain or optic vesicle using an electroporation technique, leaving the other side as a control. EGFP expression can be seen on the electroporated side of the chick brain within 24hours. Expression of the dominant negative construct in cultures of chick limb bud mesenchyme results in total block of cascade blue transfer when injected into transfected cells. Expression of both wild type and dominant negative constructs in the developing chick retina perturbs the normal development of the eye.     

Protocadherin‐17 function in Zebrafish retinal development

Cadherin cell adhesion molecules play crucial roles in vertebrate development including the development of the retina. Most studies have focused on examining functions of classic cadherins (e.g. N‐cadherin) in retinal development. There is little information on the function of protocadherins in the development of the vertebrate visual system. We previously showed that protocadherin‐17 mRNA was expressed in developing zebrafish retina during critical stages of the retinal development. To gain insight into protocadherin‐17 function in the formation of the retina, we analyzed eye development and differentiation of retinal cells in zebrafish embryos injected with protocadherin‐17 specific antisense morpholino oligonucleotides (MOs). Protocadherin‐17 knockdown embryos (pcdh17 morphants) had significantly reduced eyes due mainly to decreased cell proliferation. Differentiation of several retinal cell types (e.g. retinal ganglion cells) was also disrupted in the pcdh17 morphants. Phenotypic rescue was achieved by injection of protocadherin‐17 mRNA. Injection of a vivo‐protocadherin‐17 MO into one eye of embryonic zebrafish resulted in similar eye defects. Our results suggest that protocadherin‐17 plays an important role in the normal formation of the zebrafish retina. © 2012 Wiley Periodicals, Inc. Develop Neurobiol, 2013     

Effect of transverse gravitational loads on the vessels of the retinal membrane of the rabbit eyeball]

Changes in the eye ball retina were studied in 3 series of experiments in cleared preparations after exposure of the animal to gravitation stress of transversal direction. Prolonged single functionally endurable stress of ventro-dorsal direction (10 units/3 min) caused dilatation of the retina vessels, worse filling of peripheral parts of the circulatory bed, uneven staining of the vascular wall, constriction and dilatation along the course of the vessel. More continuous exposure to the same value of stresses (10 units up to the animal's death) resulted in a pressor effect; qualitative changes in the vessels increased. Within 1,5 hour after a 3-minute-long exposure to stress the vascular bed still remained unchanged. The diameter of vessels approached normal while the general quantity of vessels was decreased and qualitative changes were well pronounced.     

Experimental induction of microphthalmia in the chick embryo with a single dose of cisplatin

Chick embryos were injected on the fifth day of incubation with 75 ng cis-diamminedichloroplatinum II (cisplatin) and killed at daily intervals. Bilateral microphthalmia appeared in 88% of the surviving embryos; the decrease in eye size was noticeable 2 or 3 days after injection. Coinciding with this, macroscopic, histological, and ultrastructural changes started to appear in the ciliary body: ciliary processes failed to form and the cells in the inner layer of the ciliary epithelium underwent degenerative changes. Changes in the retina appeared somewhat later. Despite the decreased growth rate of the whole eye the neural layer of the retina continued to grow rapidly; as a result, it formed numerous folds and acquired a glandular appearance. In the most severe cases the rapidly growing retina would invade the ciliary region and replace completely the degenerated inner layer of the ciliary epithelium. It has been shown by previous authors that intraocular pressure is a determinant of eye expansion and also that the secretion of water and ions by the ciliary epithelium is important for the maintenance of that intraocular pressure. On this basis, our results are interpreted as indicating that the primary lesion induced by cisplatin was in the ciliary epithelium and that microphthalmia was the consequence of decreased pressure. It is also concluded that the retinal changes were due to the fact that the retina continued to grow despite the lack of expansion of the eye as a whole.     

Ciliary margin transdifferentiation from neural retina is controlled by canonical Wnt signaling

The epithelial layers of the ciliary body (CB) and iris are non-neural structures that differentiate from the anterior region of the eyecup, the ciliary margin (CM). We show here that activation of the canonical Wnt signaling pathway is sufficient and necessary for the normal development of anterior eye structures. Pharmacological activation of beta-catenin signaling with lithium (Li(+)) treatment in retinal explants in vitro induced the ectopic expression of the CM markers Otx1 and Msx1. Cre-mediated stabilization of beta-catenin expression in the peripheral retina in vivo induced a cell autonomous upregulation of CM markers at the expense of neural retina (NR) markers and inhibited neurogenesis. Consistent with a cell autonomous conversion to peripheral eye fates, the proliferation index in the region of the retina that expressed stabilized beta-catenin was identical to the wild-type CM and there was an expansion of CB-like structures at later stages. Conversely, Cre-mediated inactivation of beta-catenin reduced CM marker expression as well as the size of the CM and CB/iris. Aberrant CB development in both mouse models was also associated with a reduction in the number of retinal stem cells in vitro. In summary, activation of canonical Wnt signaling is sufficient to promote the development of peripheral eyecup fates at the expense of the NR and is also required for the normal development of anterior eyecup structures.     

The developing visual system and metamorphosis in the lamprey

Metamorphosis of the sea lamprey, Petromyzon marinus, is a true metamorphosis. The larval lamprey is a filter-feeder who dwells in the silt of freshwater streams and the adult is an active predator found in large lakes or the sea. The transformation usually occurs in the fifth or sixth year of life. Enlargement of the eye has been long accepted as a distinctive indication of metamorphosis in the sea lamprey, but it had been thought that this was because eye development in the larva was arrested after the formation of only the small central region. Recent studies indicate that all of the retina begins its development in the larva and that ganglion, amacrine, and horizontal cells differentiate in the peripheral retina of the larva. Retinal development is arrested during the premetamorphic period, to be resumed during metamorphosis. Metamorphic contributions include the differentiation of photoreceptor and bipolar cells. With the early appearance of ganglion cells, retinal pathways to the thalamus and tectum are established in larvae, as is a centripetal pathway. Tectal development spans the larval period but a spurt in tectal growth and differentiation is correlated with the completion of the retinal circuitry late in metamorphosis. The metamorphic changes in retina and tectum complete the functional development of the visual system and provide for the adult lamprey's predatory and reproductive behavior.     

视网膜发育与形成的“镶嵌模型”

视网膜上不同种类的神经细胞为秩序分布.在胚胎发育过程中,如何能形成这种有秩序的空间分布对于眼睛和视网膜的发育至关重要.研究表明,眼睛和视网膜的发育与形成受多种基因的调控,不同的基因决定了视觉系统发育的不同结构.目前有报道认为,动物的眼睛在空间和时间上是由不同组织和不同分化的细胞镶嵌而形成的.