河川沙塘鳢视觉器官的发育及其与摄食的关系

利用光学显微镜观察了河川沙塘鳢(Odontobutis potamophila)视觉器官的发育,并对其发育与摄食的关系进行了研究。河川沙塘鳢的眼囊起源于神经外胚层。当胚胎发育至心跳期时,眼囊内陷形成视杯;之后,视杯内表面的外胚层形成晶状体而与视杯分离,视杯进一步发育形成视网膜。随着胚胎的进一步发育,晶状体的直径增加,结构逐步发育完善。胚胎发育至眼黑色素出现期时,视网膜分化为6层,其中,外核层、内核层和神经节细胞层3个核层明显;胚胎发育至孵化前期时,视网膜已分化为10层。孵出后1d的仔鱼,其视网膜已能行使功能,仔鱼逐渐开口摄食。随着稚、幼鱼的发育,视网膜厚度进一步增加,结构发育完善。视网膜的结构和视觉特性显示河川沙塘鳢是要求光照条件好、白昼活动并具有较好视觉功能的鱼类。     

胭脂鱼眼早期形态发生研究

采用组织学方法观察了胭脂鱼(Myxocyprinus asiaticus) 眼的发生过程, 结果显示: 胭脂鱼眼的发育经历了眼原基形成期、眼囊形成期、视杯形成期、晶体板形成期、晶体囊形成期、角膜原基形成期、角膜上皮形成期、视网膜细胞增殖期、晶状体成熟期、眼色素形成期以及眼成型期等11个时期。视网膜发育最早, 起始于眼原基的形成, 直至眼成型期分化完成, 形成了厚度不一的8层细胞, 由内向外依次为神经纤维层、神经细胞层、内网层、内核层、外网层、外核层、视杆视锥层和色素上皮层, 且发育历时最长, 约264h。晶状体的发育在视网膜之后, 始于晶体板的形成, 于出膜前期成熟, 发育历时最短, 约74h。角膜发育最晚, 始于角膜原基的形成, 出膜1 d分化为透明的成熟角膜, 发育历时约96h。出膜4 d仔鱼眼色素沉积明显, 视网膜各层分化明显, 晶状体内部完全纤维化, 眼的形态结构基本发育完全。     

Prenatal development of the microphthalmic eye in the golden hamster

Prenatal development of the eye in a microphthalmic hamster strain (“anophthalmic white”) is compared with established normal developmental periods. The mutant eye primordium is first distinguished at an average of ten gestational days (Period 6) by an incompletely invaginated optic cup, uniformly pseudostratified outer neuroepithelial layer and widely separated margins of the optic fissure. The outer layer of the mutant cup subsequently becomes abnormally thickened, especially posteriorly and midventrally, and, except in a few eyes with localized imperfect fusion, the optic fissure is unfused at twelve days (Period 9), by which time fusion is normally complete. At 13 to 15 days (Periods 10–11) the fissure is unfused or irregularly fused in regions of variable location and extent. The occurrence of fissure fusion with concomitant loss of continuity between inner and outer epithelial layers is generally restricted to expanded anterior regions in 14–16 day (Periods 11–12) eyes. The presence of presumptive neural retina in the outer layer of the cup characterizes the mutant eye; and to varying degrees, in day 13–16 eyes, the presumptive neural retina (1) provides persistent continuity between the two cup layers, (2) forms both fused and unfused margins of the optic fissure, and (3) extends into an outer position of the optic cup. As early as 13 days (Period 10), nerve fibers are present in the outer layer of the cup, and by the last prenatal and first postnatal days (Period 12), ectopic nerve fiber bundles are widely distributed.     

Interaction of the mutant aphakia, fidget and ocular retardation genes in mice

The phenogenetic analysis of the effects of aphakia (ak) gene and its interaction with the ocular retardation (or) and fidget (fi) genes suggests that the ak gene acts in the lens cells with the result of arresting lens fibre differentiation. In mice homozygous for ak, the lens failure leads to secondary retina defects, in particular, to formation of retinal folds. In ak/ak or/or mice, the lens and retina morphogenesis stops at the optic cup stage, the eye is strongly reduced in size and more affected, compared to the corresponding single homozygotes. Unlike ak/ak or/or, in the ak/ak fi/fi mice the eyes are more regular in shape than those in the ak/ak +/+ condition. The fi gene inhibition of the retina anlage growth leads to some improvement of the eye development in double ak/ak fi/fi homozygotes, due to the absence of extensive retina folding.     

Retinal homeobox genes and the role of cell proliferation in cavefish eye degeneration

The teleost Astyanax mexicanus exhibits eyed surface dwelling (surface fish) and blind cave dwelling (cavefish) forms. Despite lacking functional eyes as adults, cavefish embryos form eye primordia, which later arrest in development, degenerate and sink into the orbit. We are comparing the expression patterns of various eye regulatory genes during surfacefish and cavefish development to determine the cause of eye degeneration. Here we examine Rx and Chx/Vsx family homeobox genes, which have a major role in cell proliferation in the vertebrate retina. We isolated and sequenced a full-length RxcDNA clone (As-Rx1) and part of a Chx/Vsx(As-Vsx2) gene, which appear to be most closely related to the zebrafish Rx1 and Alx/Vsx2 genes respectively. In situ hybridization shows that these genes have similar but non-identical expression patterns during Astyanax eye development. Expression is first detected in the optic vesicle, then throughout the presumptive retina of the optic cup, and finally in the ciliary marginal zone (CMZ), the region of the growing retina where most new retinoblasts are formed. In addition, As-Rx1 is expressed in the outer nuclear layer (ONL) of the retina, which contains the photoreceptor cells, and As-Vsx2 is expressed in the inner nuclear layer, probably in the bipolar cells. With the exception of reduced As-Rx-1 expression in the ONL, the As-Rx1 and As-Vsx2 expression patterns were unchanged in the developing retina of two different cavefish populations, suggesting that cell proliferation is not inhibited. These results were confirmed by using PCNA and BrdU markers for retinal cell division. We conclude that the CMZ is active in cell proliferation long after eye growth is diminished and is therefore not the major cause of eye degeneration.     

Immunohistochemical study of fibronectin localization during the formation of the vascular coat under the influence of the pigment epithelium in chick embryos

The role of fibronectin (FN) in cell interactions of retinal pigment epithelium (RPE) and mesenchyme surrounding the optic cup during choroid formation in chick embryos was studied by indirect immunofluorescence using antibodies against FN. Experimental coloboma of retina and choroid was used as a model. During the initial stages of coloboma the regions structured like retina rudiment appear in the outer layer of the optic cup. Such regions were formed in microphthalmic eyes obtained by excision of lens from the eyes of 3.5 day old chick embryos (stage 21). At stage 21 bright FN-specific immunofluorescence was observed in basal membrane located along the external surface of the normally differentiated RPE. Later on, FN-specific immunofluorescence appeared in mesenchyme condensing along the RPE. The most intensive FN-specific immunofluorescence was observed in chorio-capillary layer of choroid after 5-7 days of incubation. In microphthalmic eyes retina-like regions of RPE and adjacent mesenchyme showed negative reaction, and the choroid was not formed from the adjacent mesenchyme in such zones. The data obtained suggest that the presence of normally differentiated RPE producing FN-containing basal membrane is necessary for the formation of chorio-capillary layer of the choroid in chick embryos.     

The role of cell death during morphogenesis of the mammalian eye

Serial sections of embryonic rat eyes were stained with hematoxylin and eosin, quantified (by counting pycnotic and viable nuclei), reproduced by camera lucida on wax plates, and moulded into reconstructions in order to study the normal progression of cellular death during morphogenesis. At least nine distinct necrotic loci (A through I) can be distinguished. Immediately following contact between the retina and surface ectoderm (day 11) degenerating cells were observed in (A) the ventral extent of the optic vesicle, beginning in the mid-retinal primordium and continuing ventrally in the optic stalk, (B) in the rostral optic stalk base, and (C) in the surface ectoderm encircling the early lens placode. No degeneration was observed in the dorsal half of the presumptive retina, in the entire pigment epithelium, or in the lens placode proper. During day 11.5 the lens placode thickens and forms a degenerating locus (D) in its ventral portion opposite the underlying pycnotic zone in the retina (A). During day 12 the ventral pycnotic zone (A) divides into two subunits (A₁ and A₂). Invagination of the lens displaces its marginal and ventral components (C and D) so that they come to occupy the lens pore area and presumptive corneal epithelium. Simultaneous invagination of the retinal rudiment juxtaposes the pigment epithelium which concurrently forms a necrotic area (E) adjacent ventrally to that in the retina (A₁). Degeneration appears in the caudal optic stalk (I). The density of viable cells decreases adjacent to pycnotic areas in the retina and pigment epithelium and increases within these death centers. During day 13 the optic fissure forms within the subunits of the ventral pycnotic zone (A₁ and A₂). Degenerations are seen in the dorsal optic stalk (F) and in the walls of the optic fissure (G and H). Throughout these stages necrosis appears only in those portions of the eye rudiment where invagination is either retarded or completely absent. In part, these observations suggest that cell death serves (1) to retard or inhibit invagination within death centers, (2) to integrate the series of invaginations which mould the dorsal optic cup and optic fissure, (3) to assist formation of the pigment epithelium monolayer, and (4) to orient the lens vesicle within the eye cup. The spatio-temporal relationship between necrotic loci suggests that pycnotic cells in the retina may influence their production in the lens and pigment epithelium. Preliminary observations on the mouse, pig, and human substantiate those on the rat.     

A complex choreography of cell movements shapes the vertebrate eye

Optic cup morphogenesis (OCM) generates the basic structure of the vertebrate eye. Although it is commonly depicted as a series of epithelial sheet folding events, this does not represent an empirically supported model. Here, we combine four-dimensional imaging with custom cell tracking software and photoactivatable fluorophore labeling to determine the cellular dynamics underlying OCM in zebrafish. Although cell division contributes to growth, we find it dispensable for eye formation. OCM depends instead on a complex set of cell movements coordinated between the prospective neural retina, retinal pigmented epithelium (RPE) and lens. Optic vesicle evagination persists for longer than expected; cells move in a pinwheel pattern during optic vesicle elongation and retinal precursors involute around the rim of the invaginating optic cup. We identify unanticipated movements, particularly of central and peripheral retina, RPE and lens. From cell tracking data, we generate retina, RPE and lens subdomain fate maps, which reveal novel adjacencies that might determine corresponding developmental signaling events. Finally, we find that similar movements also occur during chick eye morphogenesis, suggesting that the underlying choreography is conserved among vertebrates.     

Retina mediators in fresh-water mollusc Lymnaeae stagnalis

Retrograde staining of the Lymnaeae stagnalis retina with neurobiotin has shown that most photoreceptor cells send axons to optic nerve without intermediate contacts. A part of these photoreceptors have immunireactivity to glutamate that possibly provides synaptic transmission of visual signal to central neurons. Other photoreceptors stained through optic nerve seem to have different transmitter systems. In some retina cell, but not in optic nerve fibers, immunoreactivity to pigment-dispersing hormone has been revealed. In tissues surrounding the eye cup numerous serotonin-containing fibers are present, a part of them penetrating the retina basal layer. Some of them belong to central neurons responsible for efferent innervation of the pond snail eye. It is suggested that the serotoninergic innervation as well as the cell containing the pigment-dispersing hormone are included in the mechanism of regulation of light sensitivity of the mollusc eye.     

Fine structure of the dioptric apparatus in the stalk eye of Onchidium verruculatum (Gastropoda, Stylommatophora): a distinct lamellar substructure of the lens

 The dioptric apparatus of the stalk eye in Onchidium verruculatum, including a tentacular epidermis, a cornea, and a lens, was examined using transmission electron microscopy. The tentacular epidermis was formed by columnar epidermal cells, sensory dendrites, and glandular cells. The cornea was an anterior part of the eye vesicle and consisted of corneal cells which contained abundant glycogen particles but no dark pigment granules in their cytoplasm. An acellular, transparent, ellipsoidal lens was located in the center of the eye vesicle. The lens showed a marginal zone, an outer zone, a transitional zone, an inner zone, and a central region arranged concentrically. The outer zone was the most intense electron-dense region and was finely granular in structure. The marginal zone was also finely granular and surrounded the outer zone with many hair-like slender strands on the retinal side. Toward the center of the lens this homogeneous fine granularity gradually changed into globular or rod-like substructures, about 30 nm in diameter, and then abruptly transformed into a lamellar substructure of about 30 nm in thickness. The inner zone contained a mosaic of lamellar substructures which were arranged in a fingerprint pattern that was particularly enhanced with periodic acid methenamine silver proteinate staining. The center itself consisted of deformed lamellar substructures. The concentric arrangement of substructures inside the lens of the O. ver-ruculatum stalk eye is probably responsible for the concentration and/or refraction of light. Accepted: 5 December 1997     

Role of apoptosis and mitosis during human eye development

The spatial and temporal distribution as well as ultrastructural and biochemical characteristics of apoptotic and mitotic cells during human eye development were investigated in 14 human conceptuses of 4-9 postovulatory weeks, using electron and light microscopy. In the 5th developmental week, apoptotic and mitotic cells were found in the neuroepithelium of the optic cup and stalk, being the most numerous at the borderline between the two layers of the optic cup, and at the place of transition of the optic cup into stalk. They were also found at the region of detachment of the lens pit from the surface ectoderm. In the later developmental stages (the 6th-the 9th week), apoptotic and mitotic cells were observed in the neural retina and the anterior lens epithelium. Throughout all stages examined, mitotic cells were found exclusively adjacent to the lumen either of the intraretinal space or the optic stalk ventricle, or were restricted to the superficial epithelial layer of the lens primordium. Unlike mitotic cells, apoptotic cells occurred throughout the whole width both of the neuroepithelium and the surface epithelium. Ultrastructurally, apoptotic cells were characterised by round- or crescent-shaped condensations of chromatin near the nuclear membrane, while in the more advanced stages of apoptosis by apoptotic bodies. The distribution of caspase-3-positive cells coincided with the location of apoptotic cells described by morphological techniques indicating that the caspase-3-dependent apoptotic pathway operates during the all stages of human eye development. The location of cells positive for anti-apoptotic bcl-2 protein was in accordance with the regions of eye with high mitotic activity, confirming the role of bcl-2 in protecting cells from apoptosis. In the earliest stage of eye development, apoptosis and mitosis might be associated with the sculpturing of the walls of optic cup and stalk, while high mitotic activity along the intraretinal space and optic stalk ventricle indicates its role in the gradual luminal closure. These processes also participate in the detachment of the lens pit epithelium from the surface ectoderm as well as in further closure of the lens vesicle. Later on, both processes seem to be involved in the neural retina differentiation, lens morphogenesis and secondary lens fibre differentiation.     

Structure of the eye of Haideotriton wallacei, a North American troglobitic salamander

The eye of Haideotriton wallacei is more reduced histologically than those of othe troglobitic salamanders. The tiny eye is imbedded in a mass of adipose tissue. No extrinsic eye muscles are present. A rudimentary lens is present in about half of the eyes examined. In two instances the lens is surrounded by a small chamber; most eyes lack a chamber. The retina and iris are relatively undifferentiated. The relatively massive retina lacks rods and cones, an outer plexiform layer and subdivided nuclear layers. A tiny optic nerve runs to the brain.     

The lens controls cell survival in the retina: Evidence from the blind cavefish Astyanax

The lens influences retinal growth and differentiation during vertebrate eye development but the mechanisms are not understood. The role of the lens in retinal growth and development was studied in the teleost Astyanax mexicanus, which has eyed surface-dwelling (surface fish) and blind cave-dwelling (cavefish) forms. A lens and laminated retina initially develop in cavefish embryos, but the lens dies by apoptosis. The cavefish retina is subsequently disorganized, apoptotic cells appear, the photoreceptor layer degenerates, and retinal growth is arrested. We show here by PCNA, BrdU, and TUNEL labeling that cell proliferation continues in the adult cavefish retina but the newly born cells are removed by apoptosis. Surface fish to cavefish lens transplantation, which restores retinal growth and rod cell differentiation, abolished apoptosis in the retina but not in the RPE. Surface fish lens deletion did not cause apoptosis in the surface fish retina or affect RPE differentiation. Neither lens transplantation in cavefish nor lens deletion in surface fish affected retinal cell proliferation. We conclude that the lens acts in concert with another optic component, possibly the RPE, to promote retinal cell survival. Accordingly, deficiency in both optic structures may lead to eye degeneration in cavefish.     

The Msh-like homeobox genes define domains in the developing vertebrate eye.

The mouse Hox-7.1 gene has previously been shown to be related to the Drosophila Msh homeobox-containing gene. Here we report the isolation of a new member of this family which resides at an unlinked chromosomal location and has been designated Hox-8.1. Both Hox-7.1 and Hox-8.1 are expressed in the mouse embryo during the early stages of eye development in a distinct spatial and temporal relationship. Hox-8.1 is expressed in the surface ectoderm and in the optic vesicle before invagination occurs in regions corresponding to the prospective corneal epithelium and neural retina, respectively. Hox-7.1 is expressed after formation of the optic cup, marking the domain that will give rise to the ciliary body. The activity of these genes indicates that the inner layer of the optic cup is differentiated into three distinct compartments before overt cellular differentiation occurs. Our results suggest that these genes are involved in defining the region that gives rise to the inner layer of the optic cup and in patterning this tissue to define the iris, ciliary body and retina.     

Asymmetries in the sense organs and central nervous system of the squid Histioteuthis

The visual system of Histioteuthis is markedly asymmetrical, in that the eyes and optic lobes are considerably larger on the left side, and the lens of the left eye is often yellower in colour than that of the right eye. At the histological level, the rhabdomes of the retinas of both eyes show the usual rectilinear pattern typical of cephalopods. Unlike other species described, however, the orientation of the pattern is not uniform over the retina. The optic lobes are well developed on both sides, again following the typical squid pattern, although the plexiform and inner granular layers are thicker on the left side. In life it is likely that the animals orient at an oblique angle with the arms downward, and the left eye pointing upwards and the right eye downwards, and the asymmetries of the visual system are probably related to this posture. No corresponding asymmetries in the statocysts or other parts of the central nervous system have, however, been detected     

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 of the eye in the turbot Psetta maxima (Teleosti) from hatching through metamorphosis

Development of the eyes during the larval and metamorphic stages of the turbot Psetta maxima (Teleosti) was studied using microscopy. Events during differentiation of both eyes occur simultaneously, and no differences between he migrating and no-migrating eye were observed during metamorphosis. At hatching, the eyes are rudimentary, consisting of a neuroepithelial optic cup and a small lens. During larval development, major changes occur in the lens and retina, in which cones are the only photoreceptors. The appearance of rods is delayed until metamorphosis. The outer ocular layers (sclera and choroid) arise during larval development as thin connective layers with little differentiation. These layers undergo important changes just before and during metamorphosis. These results indicate that development of the individual components of the eye occurs at different times. Those of ectodermal origin appear early, providing a simple visual organ during larval life. By metamorphosis, the eye shows adult characteristics, including two types of photoreceptors, a rich choroid vascular supply and ocular structures involved in protecting, shaping, and moving the eye. J Morphol 233:31–42, 1997. © 1997 Wiley-Liss, Inc.     

Noggin producing, MyoD-positive cells are crucial for eye development

A subpopulation of cells expresses MyoD mRNA and the cell surface G8 antigen in the epiblast prior to the onset of gastrulation. When an antibody to the G8 antigen was applied to the epiblast, labeled cells were later found in the ocular primordia and muscle and non-muscle forming tissues of the eyes. In the lens, retina and periocular mesenchyme, G8-positive cells synthesized MyoD mRNA and the bone morphogenetic protein inhibitor Noggin. MyoD expressing cells were ablated in the epiblast by labeling them with the G8 MAb and lysing them with complement. Their ablation in the epiblast resulted in eye defects, including anopthalmia, micropthalmia, altered pigmentation and malformations of the lens and/or retina. The right eye was more severely affected than the left eye. The asymmetry of the eye defects in ablated embryos correlated with differences in the number of residual Noggin producing, MyoD-positive cells in ocular tissues. Exogenously supplied Noggin compensated for the ablated epiblast cells. This study demonstrates that MyoD expressing cells serve as a Noggin delivery system to regulate the morphogenesis of the lens and optic cup.