Molecular regulators involved in vertebrate eye development

The role of FYCO1-dependent autophagy in lens fiber cell differentiation

FYCO1 (FYVE and coiled-coil domain containing 1) is an adaptor protein, expressed ubiquitously and required for microtubule-dependent, plus-end-directed transport of macroautophagic/autophagic vesicles. We have previously shown that loss-of-function mutations in FYCO1 cause cataracts with no other ocular and/or extra-ocular phenotype. Here, we show fyco1 homozygous knockout (fyco1-/-) mice recapitulate the cataract phenotype consistent with a critical role of FYCO1 and autophagy in lens morphogenesis. Transcriptome coupled with proteome and metabolome profiling identified many autophagy-associated genes, proteins, and lipids respectively perturbed in fyco1-/- mice lenses. Flow cytometry of FYCO1 (c.2206C>T) knock-in (KI) human lens epithelial cells revealed a decrease in autophagic flux and autophagic vesicles resulting from the loss of FYCO1. Transmission electron microscopy showed cellular organelles accumulated in FYCO1 (c.2206C>T) KI lens-like organoid structures and in fyco1-/- mice lenses. In summary, our data confirm the loss of FYCO1 function results in a diminished autophagic flux, impaired organelle removal, and cataractogenesis.Abbreviations: CC: congenital cataracts; DE: differentially expressed; ER: endoplasmic reticulum; FYCO1: FYVE and coiled-coil domain containing 1; hESC: human embryonic stem cell; KI: knock-in; OFZ: organelle-free zone; qRT-PCR: quantitative real-time PCR; PE: phosphatidylethanolamine; RNA-Seq: RNA sequencing; SD: standard deviation; sgRNA: single guide RNA; shRNA: shorthairpin RNA; TEM: transmission electron microscopy; WT: wild type.

Clinical spectrum of non-syndromic microphthalmos, anophthalmos and coloboma in the paediatric population: a multicentric study from North India

AIMS

To describe the clinical features, visual acuity and causes of ocular morbidity in children (0-18 years) with microphthalmos, anophthalmos, and coloboma (MAC) from North India.

METHODS

A retrospective study conducted between October 2017 and September 2018 in three tertiary eye institutes, part of the Bodhya Eye Consortium with consensus led common pro formas. Children with complete clinical data and without syndromic/systemic involvement were included. The clinical phenotype was divided into isolated ocular coloboma (CB), coloboma with microcornea (CBMC), colobomatous microphthalmos (CBMO), non-colobomatous microphthalmos (MO) and anophthalmos (AO).

RESULTS

A total of 532 children with MAC were examined. Seventeen records were excluded due to incomplete data (0.2%). 515 children (845 eyes) were included: 54.4% males and 45.6% females. MAC was unilateral in 36% and bilateral in 64%. CB, CBMC, CBMO, MO and AO were seen in 26.4%, 31%, 22%, 8% and 12.5% of eyes, respectively. Nystagmus was found in 40%, strabismus in 23%, cataract in 18.7% and retinal detachment in 15%. Best-corrected visual acuity (BCVA) of <3/60 was seen in 62.4% eyes. Blindness (BCVA <3/60 in better eye) was seen in 42.8% of bilateral patients. Those with microcornea or microphthalmos with coloboma had worse BCVA (p<0.001). There were regional differences in the type of MAC phenotype presenting to the three institutes.

CONCLUSION

The MAC group of disorders cause significant ocular morbidity. The presence of microcornea or microphthalmos with coloboma predicts worse BCVA. The variation of the MAC phenotype with the district of origin of the patient raises questions of aetiology and is subject to further studies.

Meta-analysis of 542,934 subjects of European ancestry identifies new genes and mechanisms predisposing to refractive error and myopia

Refractive errors, in particular myopia, are a leading cause of morbidity and disability worldwide. Genetic investigation can improve understanding of the molecular mechanisms that underlie abnormal eye development and impaired vision. We conducted a meta-analysis of genome-wide association studies (GWAS) that involved 542,934 European participants and identified 336 novel genetic loci associated with refractive error. Collectively, all associated genetic variants explain 18.4% of heritability and improve the accuracy of myopia prediction (area under the curve (AUC) = 0.75). Our results suggest that refractive error is genetically heterogeneous, driven by genes that participate in the development of every anatomical component of the eye. In addition, our analyses suggest that genetic factors controlling circadian rhythm and pigmentation are also involved in the development of myopia and refractive error. These results may enable the prediction of refractive error and the development of personalized myopia prevention strategies in the future.

Localization of Tfap2β, Casq2, Penk, Zic1, and Zic3 Expression in the Developing Retina, Muscle, and Sclera of the Embryonic Mouse Eye

Optic development involves sequential interactions between several different tissue types, including the overlying ectoderm, adjacent mesoderm, and neural crest mesenchyme and the neuroectoderm. In an ongoing expression screen, we identified that Tfap2β, Casq2, Penk, Zic1, and Zic3 are expressed in unique cell types in and around the developing eye. Tfap2β, Zic1, and Zic3 are transcription factors, Casq2 is a calcium binding protein and Penk is a neurotransmitter. Tfap2β, Zic1, and Zic3 have reported roles in brain and craniofacial development, while Casq2 and Penk have unknown roles. These five genes are expressed in the major tissue types in the eye, including the muscles, nerves, cornea, and sclera. Penk expression is found in the sclera and perichondrium. At E12.5 and E15.5, the extra-ocular muscles express Casq2, the entire neural retina expresses Zic1, and Zic3 is expressed in the optic disk and lip of the optic cup. The expression of Tfap2β expanded from corneal epithelium to the neural retina between E12.5 to E15.5. These genes are expressed in similar domains as Hedgehog (Gli1, and Ptch1) and the Wnt (Lef1) pathways. The expression patterns of these five genes warrant further study to determine their role in eye morphogenesis.

An update on the genetics of ocular coloboma

Ocular coloboma is an uncommon, but often severe, sight-threatening condition that can be identified from birth. This congenital anomaly is thought to be caused by maldevelopment of optic fissure closure during early eye morphogenesis. It has been causally linked to both inherited (genetic) and environmental influences. In particular, as a consequence of work to identify genetic causes of coloboma, new molecular pathways that control optic fissure closure have now been identified. Many more regulatory mechanisms still await better understanding to inform on the development of potential therapies for patients with this malformation. This review provides an update of known coloboma genes, the pathways they influence and how best to manage the condition. In the age of precision medicine, determining the underlying genetic cause in any given patient is of high importance.

[Bilateral chorioretinian colobome: about a case]

La présence d'un colobome choriorétinien soulève souvent des problèmes cliniques entraînant parfois une certaine confusion. Néanmoins, le diagnostic se doit d'être aussi précis que possible pour plusieurs raisons. L'association de certaines anomalies congénitales de la papille avec d'autres pathologies neurologiques endocriniennes ou systémiques et le problème de diagnostic différentiel avec d'autres pathologies ophtalmologiques. Nous rapportons un cas clinique d'un enfant âgé de 6 ans, le premier garçon d'une famille de 2 enfants présentant un colobome papillaire bilatéral sans d'autres anomalies malformatives associées. Dans ses antécédents: sont accouchement s'est déroulé normalement et sont statut vaccinal été à jour. L'examen ophtalmologique de son père et de sa petite sœur âgée de 4 ans été sans particularité, cependant sa mère présente un strabisme divergent à l'œil droit.

Nosip functions during vertebrate eye and cranial cartilage development

BACKGROUND

The nitric oxide synthase interacting protein (Nosip) has been associated with diverse human diseases including psychological disorders. In line, early neurogenesis of mouse and Xenopus is impaired upon Nosip deficiency. Nosip knockout mice show craniofacial defects and the down-regulation of Nosip in the mouse and Xenopus leads to microcephaly. Until now, the exact underlying molecular mechanisms of these malformations were still unknown.

RESULTS

Here, we show that nosip is expressed in the developing ocular system as well as the anterior neural crest cells of Xenopus laevis. Furthermore, Nosip inhibition causes severe defects in eye formation in the mouse and Xenopus. Retinal lamination as well as dorso-ventral patterning of the retina were affected in Nosip-depleted Xenopus embryos. Marker gene analysis using rax, pax6 and otx2 reveals an interference with the eye field induction and differentiation. A closer look on Nosip-deficient Xenopus embryos furthermore reveals disrupted cranial cartilage structures and an inhibition of anterior neural crest cell induction and migration shown by twist, snai2, and egr2. Moreover, foxc1 as downstream factor of retinoic acid signalling is affected upon Nosip deficiency.

CONCLUSIONS

Nosip is a crucial factor for the development of anterior neural tissue such the eyes and neural crest cells. Developmental Dynamics 247:1070-1082, 2018. © 2018 Wiley Periodicals, Inc.

Frizzled 3 acts upstream of Alcam during embryonic eye development

Formation of a functional eye during vertebrate embryogenesis requires different processes such as cell differentiation, cell migration, cell-cell interactions as well as intracellular signalling processes. It was previously shown that the non-canonical Wnt receptor Frizzled 3 (Fzd3) is required for proper eye formation, however, the underlying mechanism is poorly understood. Here we demonstrate that loss of Fzd3 induces severe malformations of the developing eye and that this defect is phenocopied by loss of the activated leukocyte cell adhesion molecule (Alcam). Promoter analysis revealed the presence of a Fzd3 responsive element within the alcam promoter, which is responsible for alcam expression during anterior neural development. In-depth analysis identified the jun N-terminal protein kinase 1 (JNK1) and the transcription factor paired box 2 (Pax2) to be important for the activation of alcam expression. Altogether our study reveals that alcam is activated through non-canonical Wnt signalling during embryonic eye development in Xenopus laevis and shows that this pathway plays a similar role in different tissues.

Regulation of the neural niche by the soluble molecule Akhirin

Though the adult central nervous system has been considered a comparatively static tissue with little turnover, it is well established today that new neural cells are generated throughout life. Neural stem/progenitor cells (NS/PCs) can self-renew and generate all types of neural cells. The proliferation of NS/PCs, and differentiation and fate determination of PCs are regulated by extrinsic factors such as growth factors, neurotrophins, and morphogens. Although several extrinsic factors that influence neurogenesis have already been reported, little is known about the role of soluble molecules in neural niche regulation. In this review, we will introduce the soluble molecule Akhirin and discuss its role in the eye and spinal cord during development.

Development of astrocytes in the vertebrate eye

Astrocytes represent the earliest glial population in the embryonic optic nerve, contributing critically to retinal angiogenesis and formation of brain-retinal-barrier. Despite of many developmental and clinical implications of astrocytes, answers to some of the most fundamental questions of this unique type of glial cells remain elusive. This review provides an overview of the current knowledge about the origination, proliferation, and differentiation of astrocytes, their journey from the optic nerve toward the neuroretina, and their involvement in physiological and pathological development of the visual system.

Aberrant activation of p53 due to loss of MDM2 or MDMX causes early lens dysmorphogenesis

Although forming a heterodimer or heterooligomer is essential for MDM2 and MDMX to fully control p53 during early embryogenesis, deletion of either MDM2 or MDMX in specific tissues using the loxp-Cre system reveals phenotypic diversity during organ morphogenesis, which can be completely rescued by loss of p53, suggesting the spatiotemporal independence and specificity of the regulation of p53 by MDM2 and MDMX. In this study, we investigated the role of the MDM2-MDMX-p53 pathway in the developing lens that is a relatively independent region integrating cell proliferation, differentiation and apoptosis. Using the mice expressing Cre recombinase specifically in the lens epithelial cells (LECs) beginning at E9.5, we demonstrated that deletion of either MDM2 or MDMX induces apoptosis of LEC and reduces cell proliferation, resulting in lens developmental defect that finally progresses into aphakia. Specifically, the lens defect caused by MDM2 deletion was evident at E10, occurring earlier than that caused by MDMX deletion. These lens defects were completely rescued by loss of two alleles of p53, but not one allele of p53. These results demonstrate that both MDM2 and MDMX are required for monitoring p53 activity during lens development, and they may function independently or synergistically to control p53 and maintain normal lens morphogenesis.

Side chain modified peptide nucleic acids (PNA) for knock-down of six3 in medaka embryos

BACKGROUND

Synthetic antisense molecules have an enormous potential for therapeutic applications in humans. The major aim of such strategies is to specifically interfere with gene function, thus modulating cellular pathways according to the therapeutic demands. Among the molecules which can block mRNA function in a sequence specific manner are peptide nucleic acids (PNA). They are highly stable and efficiently and selectively interact with RNA. However, some properties of non-modified aminoethyl glycine PNAs (aegPNA) hamper their in vivo applications.

RESULTS

We generated new backbone modifications of PNAs, which exhibit more hydrophilic properties. When we examined the activity and specificity of these novel phosphonic ester PNAs (pePNA) molecules in medaka (Oryzias latipes) embryos, high solubility and selective binding to mRNA was observed. In particular, mixing of the novel components with aegPNA components resulted in mixed PNAs with superior properties. Injection of mixed PNAs directed against the medaka six3 gene, which is important for eye and brain development, resulted in specific six3 phenotypes.

CONCLUSIONS

PNAs are well established as powerful antisense molecules. Modification of the backbone with phosphonic ester side chains further improves their properties and allows the efficient knock down of a single gene in fish embryos.

Organogenesis of mild ocular coloboma in FLS mice: failure of basement membrane disintegration at optic fissure margins

Fatty Liver Shionogi (FLS) mice have been shown to develop a hereditary disorder characterized by localized retinochoroidal defects of the ventral fundus very similar to human typical ocular coloboma without microphthalmia. The objective of this study was to determine when and how the failure of the optic fissure closure occurs, and to clarify the disturbed mechanism of basement membrane disintegration during embryonal stage in FLS mice. Fetuses at day 11.5-15.5 of gestation were obtained from dams of FLS and BALB/c strain of mice. Coronal serial sections through the eye were examined by light and electron microscopy. The sections were followed by observation of the basement membrane using reaction with periodic acid-Schiff (PAS) reagent and immunohistochemical staining with anti-Laminin and anti-Type IV collagen antibodies. Both optic fissure margins closely approached each other up to GD 11.5 in all FLS and BALB/c embryos. The inner and outer layers of the optic cup did not normally fuse at midlenticular levels of the optic fissure in almost 70% of FLS fetuses by GD 15.5, whereas both margins were completely fused in all BALB/c fetuses of the same gestational day. In the FLS fetuses at GD 12.5, rolling on one side of fissure margins and consequent asymmetry were observed at the ventral optic fissure. The basement membrane persisted after the close contact of both sides of the fissure margins during GD 11.5 and 15.5. Ultrastructurally, the basal lamina was not disintegrated and mesenchymal cells intervened between the two neuroepithelial layers, resulting in complete separation of both fissure margins at GD 13.0. It is highly probable that the disturbed basement membrane disintegration right before optic fissure closure causes mild ocular coloboma without microphthalmia in FLS mice.

Differential selection within the Drosophila retinal determination network and evidence for functional divergence between paralog pairs

The retinal determination (RD) network in Drosophila comprises 14 known nuclear proteins that include DNA-binding proteins, transcriptional coactivators, kinases, and phosphatases. The composition of the network varies considerably throughout the animal kingdom, with the network in several basal insects having fewer members and with vertebrates having potentially significantly higher numbers of RD genes. One important contributing factor for the variation in gene number within the network is gene duplication. For example, 10 members of the RD network in Drosophila are derived from duplication events. Here we present an analysis of the coding regions of the five pairs of duplicate genes from within the RD network of several different Drosophila species. We demonstrate that there is differential selection across the coding regions of all RD genes. Additionally, some of the most significant differences in ratios of non-silent-to-silent site substitutions (d(N)/d(S)) between paralog pairs are found within regions that have no ascribed function. Previous structure/function analyses of several duplicate genes have identified areas within one gene that contain novel activities when compared with its paralog. The evolutionary analysis presented here identifies these same areas in the paralogs as being under high levels of relaxed selection. We suggest that sequence divergence between paralogs and selection signatures can be used as a reasonable predictor of functional changes in rapidly evolving motifs.

Retinal determination the beginning of eye development

The road to producing an eye begins with the decision to commit a population of cells to adopting an eye tissue fate, the process of retinal determination. Over the past decade and a half, a network of transcription factors has been found to mediate this process in all seeing animals. This retinal determination network is known to regulate not only tissue fate but also cell proliferation, pattern formation, compartment boundary establishment, and even retinal cell specification. The compound eye of the fruit fly, Drosophila melanogaster, has proven to be an excellent experimental system to study the mechanisms by which this network regulates organogenesis and tissue patterning. In fact the founding members of most of the gene families that make up this network were first isolated in Drosophila based on loss-of-function phenotypes that affect the eye. This chapter will highlight the history of discovery of the retinal determination network and will draw attention to the molecular and biochemical mechanisms that underlie our understanding of how the fate of the retina is determined.

Building the developmental oculome: systems biology in vertebrate eye development and disease

The vertebrate eye is a sophisticated multicomponent organ that has been actively studied for over a century, resulting in the identification of the major embryonic and molecular events involved in its complex developmental program. Data gathered so far provides sufficient information to construct a rudimentary network of the various signaling molecules, transcription factors, and their targets for several key stages of this process. With the advent of genomic technologies, there has been a rapid expansion in our ability to collect and process biological information, and the use of systems-level approaches to study specific aspects of vertebrate eye development has already commenced. This is beginning to result in the definition of the dynamic developmental networks that operate in ocular tissues, and the interactions of such networks between coordinately developing ocular tissues. Such an integrative understanding of the eye by a comprehensive systems-level analysis can be termed the 'oculome', and that of serial developmental stages of the eye as it transits from its initiation to a fully formed functional organ represents the 'developmental oculome'. Construction of the developmental oculome will allow novel mechanistic insights that are essential for organ regeneration-based therapeutic applications, and the generation of computational models for eye disease states to predict the effects of drugs. This review discusses our present understanding of two of the individual components of the developing vertebrate eye--the lens and retina--at both the molecular and systems levels, and outlines the directions and tools required for construction of the developmental oculome.

Vax2 regulates retinoic acid distribution and cone opsin expression in the vertebrate eye

Vax2 is an eye-specific homeobox gene, the inactivation of which in mouse leads to alterations in the establishment of a proper dorsoventral eye axis during embryonic development. To dissect the molecular pathways in which Vax2 is involved, we performed a transcriptome analysis of Vax2(-/-) mice throughout the main stages of eye development. We found that some of the enzymes involved in retinoic acid (RA) metabolism in the eye show significant variations of their expression levels in mutant mice. In particular, we detected an expansion of the expression domains of the RA-catabolizing enzymes Cyp26a1 and Cyp26c1, and a downregulation of the RA-synthesizing enzyme Raldh3. These changes determine a significant expansion of the RA-free zone towards the ventral part of the eye. At postnatal stages of eye development, Vax2 inactivation led to alterations of the regional expression of the cone photoreceptor genes Opn1sw (S-Opsin) and Opn1mw (M-Opsin), which were significantly rescued after RA administration. We confirmed the above described alterations of gene expression in the Oryzias latipes (medaka fish) model system using both Vax2 gain- and loss-of-function assays. Finally, a detailed morphological and functional analysis of the adult retina in mutant mice revealed that Vax2 is necessary for intraretinal pathfinding of retinal ganglion cells in mammals. These data demonstrate for the first time that Vax2 is both necessary and sufficient for the control of intraretinal RA metabolism, which in turn contributes to the appropriate expression of cone opsins in the vertebrate eye.

Molecular and cellular aspects of amphibian lens regeneration

Lens regeneration among vertebrates is basically restricted to some amphibians. The most notable cases are the ones that occur in premetamorphic frogs and in adult newts. Frogs and newts regenerate their lens in very different ways. In frogs the lens is regenerated by transdifferentiation of the cornea and is limited only to a time before metamorphosis. On the other hand, regeneration in newts is mediated by transdifferentiation of the pigment epithelial cells of the dorsal iris and is possible in adult animals as well. Thus, the study of both systems could provide important information about the process. Molecular tools have been developed in frogs and recently also in newts. Thus, the process has been studied at the molecular and cellular levels. A synthesis describing both systems was long due. In this review we describe the process in both Xenopus and the newt. The known molecular mechanisms are described and compared.

Notch signaling activation suppresses v-Src-induced transformation of neural cells by restoring TGF-β-mediated differentiation

BACKGROUND

We have been investigating how interruption of differentiation contributes to the oncogenic process and the possibility to reverse the transformed phenotype by restoring differentiation. In a previous report, we correlated the capacity of intracellular Notch (ICN) to suppress v-Src-mediated transformation of quail neuroretina (QNR/v-src(ts)) cells with the acquisition by these undifferentiated cells of glial differentiation markers.

METHODOLOGY/PRINCIPAL FINDINGS

In this work, we have identified autocrine TGF-β3 signaling activation as a major effector of Notch-induced phenotypic changes, sufficient to induce transition in differentiation markers expression, suppress morphological transformation and significantly inhibit anchorage-independent growth. We also show that this signaling is constitutive of and contributes to ex-vivo autonomous QNR cell differentiation and that its down-regulation is essential to achieve v-Src-induced transformation.

CONCLUSIONS/SIGNIFICANCE

These results support the possibility that Notch signaling induces differentiation and suppresses transformation by a novel mechanism, involving secreted proteins. They also underline the importance of extracellular signals in controlling the balance between normal and transformed phenotypes.

The spatial patterning of mouse cone opsin expression is regulated by bone morphogenetic protein signaling through downstream effector COUP-TF nuclear receptors

Cone photopigments, known as opsins, are pivotal elements and the first detection module used in color vision. In mice, cone photoreceptors are distributed throughout the retina, and short-wavelength (S) and medium-wavelength (M) opsins have unique expression patterns in the retina with a gradient along the dorsoventral axis; however, the mechanisms regulating the spatial patterning of cone opsin expression have not been well documented. The purpose of this study was to define the mechanisms regulating the spatial patterning of cone opsin expression. By analyzing knock-outs for bone morphogenetic protein (BMP) signaling, we found an essential role for BMP in forming cone opsin expression patterns in the retina; however, BMP signaling is activated only transiently in the dorsal half of the retina during early retinal development. Thus, BMP is not likely to play a direct role in opsin gene expression, which starts at a later stage of retinal development. We identified the chicken ovalbumin upstream promoter-transcription factor (COUP-TF) nuclear receptor as a link between BMP and opsin expression. BMP signaling is essential for the correct dorsoventral spatial expression of COUP-TFI and COUP-TFII. Through gain- and loss-of-function analyses, we found that both COUP-TFI and COUP-TFII are required to suppress S-opsin expression in the dorsal retina but that only COUP-TFI plays an essential role in suppressing M-opsin expression in the ventral retina. Based on these findings, we propose a new molecular cascade involving BMP and COUP-TFs that conveys dorsoventral information to direct the expression of cone opsins during retinal development.

Ocular abnormalities in mice lacking the immunoglobulin superfamily member Cdo

Vertebrate eye development requires a series of complex morphogenetic and inductive events to produce a lens vesicle centered within the bilayered optic cup and a posteriorly positioned optic stalk. Multiple congenital eye defects, including microphthalmia and coloboma, result from defects in early eye morphogenesis. Cdo is a multifunctional cell surface immunoglobulin superfamily member that interacts with and mediates signaling by cadherins and netrins to regulate myogenesis. In addition, Cdo plays an essential role in early forebrain development by functioning as coreceptor for sonic hedgehog. It is reported here that Cdo is expressed in a dynamic, but dorsally restricted, fashion during early eye development, and that mice lacking Cdo display multiple eye defects. Anomalies seen in Cdo(-/-) mice include coloboma (failure to close the optic fissure); failure to form a proper boundary between the retinal pigmented epithelium and optic stalk; defective lens formation, including failure to separate from the surface ectoderm; and microphthalmia. Consistent with this wide array of defects, developing eyes of Cdo(-/-) mice show altered expression of several regulators of dorsoventral eye patterning, including Pax6, Pax2, and Tbx5. Taken together, these findings show that Cdo is required for normal eye development and is required for normal expression of patterning genes in both the ventral and dorsal domains. The multiple eye development defects seen in Cdo(-/-) mice suggest that mutations in human Cdo could contribute to congenital eye anomalies, such as Jacobsen syndrome, which is frequently associated with ocular defects, including coloboma and Peters' anomaly.

Identification of the minimal promoter region of the mouse NKX5-3, a transcription factor implicated in eye development

Early ocular development is controlled by a complex network of transcription factors, cell cycle regulators, and diffusible signalling molecules. Together, these molecules regulate cell proliferation and apoptosis, and specify retinal fate. NKX5-3 is a homeobox transcription factor implicated in eye development. The analysis of the 5'-flanking region of the mouse Nkx5-3 gene revealed a predicted TATA-less promoter sequence between -416 and -166 of the translation start site. To functionally characterise Nkx5-3 promoter activity, serial deletions of the promoter sequence were introduced in pGL-3 basic vector and promoter activity of these 5'- and 3'-deleted constructions was tested in HeLa and CHO cells. Transactivation assays identified a region between -350 and -296 exhibiting promoter-like activity. Combined analysis by deletions and point mutations showed that this sequence, containing multiple Sp1 binding sites was necessary to promote transcriptional activity. Binding of Sp1 to this region was confirmed by electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation, using an antibody specific for Sp1. Altogether, these results demonstrated that the immediate upstream region of Nkx5-3 gene possessed a strong intrinsic promoter activity in vitro, suggesting a potential role in Nkx5-3 transcription in vivo.

Rho GDP dissociation inhibitor-mediated disruption of Rho GTPase activity impairs lens fiber cell migration, elongation and survival

To explore the role of the Rho GTPases in lens morphogenesis, we overexpressed bovine Rho GDP dissociation inhibitor (Rho GDI alpha), which serves as a negative regulator of Rho, Rac and Cdc42 GTPase activity, in a lens-specific manner in transgenic mice. This was achieved using a chimeric promoter of delta-crystallin enhancer and alpha A-crystallin, which is active at embryonic day 12. Several individual transgenic (Tg) lines were obtained, and exhibited ocular specific phenotype comprised of microphthalmic eyes with lens opacity. The overexpression of bovine Rho GDI alpha disrupted membrane translocation of Rho, Rac and Cdc42 GTPases in Tg lenses. Transgenic lenses also revealed abnormalities in the migration pattern, elongation and organization of lens fibers. These changes appeared to be associated with impaired organization of the actin cytoskeleton and cell-cell adhesions. At E14.5, the size of the Rho GDI alpha Tg lenses was larger compared to wild type (WT) and the central lens epithelium and differentiating fibers exhibited an abnormal increase of bromo-deoxy-uridine incorporation. Postnatal Tg eyes, however, were much smaller in size compared to WT eyes, revealing increased apoptosis in the disrupted lens fibers. Taken together, these data demonstrate a critical role for Rho GTPase-dependent signaling pathways in processes underlying morphogenesis, fiber cell migration, elongation and survival in the developing lens.

MARCKS-like protein, a membrane protein identified for its expression in developing neural retina, plays a role in regulating retinal cell proliferation

Membrane proteins are expressed in a specific manner in developing tissues, and characterization of these proteins is valuable because it allows them to be used as cell surface markers. Furthermore, they are potentially important for the regulation of organogenesis because some may participate in signal transduction. In the present study, we used proteomics to examine the comprehensive protein expression profile of the membrane fraction in the embryonic and adult mouse retina. We purified the retinal membrane fraction by sucrose-density-gradient centrifugation and analysed total proteins using shotgun analysis on a nanoflow LC-MS/MS (liquid chromatography tandem MS) system. Approximately half of the 326 proteins from the adult retina and a quarter of the 310 proteins from the embryonic retina (day 17) appeared to be membrane-associated proteins. Among these, MLP [MARCKS (myristoylated alanine-rich C-kinase substrate)-like protein], which shares approx. 50% amino acid identity with MARCKS, was selected for further characterization. The mRNA and surface protein expression of MLP decreased as retinal development progressed. Overexpression of MLP by retrovirus-mediated gene transfer enhanced the proliferation of retinal progenitor cells without affecting differentiation or cell migration in a retinal explant culture system. In contrast, MLP overexpression did not promote proliferation in fibroblasts (NIH 3T3 cells). Mutation analysis of MLP demonstrated that myristoylation was necessary to promote proliferation and that phosphorylation inhibited proliferation, indicating the functional importance of membrane localization.

Microscopic characterization of rat retinal progenitor cells

A progenitor cell line was developed from a postnatal day 2 (P2) rat retina to study the effects of secreted proteins of the retinal pigment epithelium (RPE) on isolated retinal progenitor cells and markers for immature and differentiated retinal cells. Progenitor cells were cloned from a P2 explant grown in secreted proteins of cultured RPE cells. A cell line was cloned from a single progenitor cell. During the period of RPE-secreted protein stimulation the cells were transformed with the psi AE1A virus. Progenitor cells formed extensive processes when grown in serum and proliferated from the explant when grown in secreted proteins of RPE cells as demonstrated by bromodeoxyuridine (BrdU). All progenitor cells at early and late passages including a cloned cell line (D4) expressed Pax6, a transcription factor essential for eye development, which was verified by Western blotting. All cells expressed nestin, an early neuroepithelial cell marker. These two traits showed the immature character of these rat retinal progenitor cells. All cells expressed the intermediate filament protein vimentin, an intermediate filament protein. Interestingly, most progenitor cells grown in serum expressed the mature cell markers opsin, but few cells expressed glial fibrillary acidic protein (GFAP). The progenitor cells responded to proteins secreted by cultured RPE cells by forming large clusters, while cells grown in retinoic acid formed long thin processes that extended from a round cell body. These progenitor cells, following treatment with secreted proteins of the RPE, will be tested for their therapeutic effect in diseased rat retinas.

Localization of a novel gene for congenital nonsyndromic simple microphthalmia to chromosome 2q11-14

Microphthalmia is a clinically and genetically heterogeneous disorder of eye development. The genetic basis of nonsyndromic microphthalmia is not yet fully understood. Previous studies indicated that disease pedigrees from different genetic backgrounds could be attributed to completely different gene loci. To investigate the etiology in a large autosomal-dominant inherited simple microphthalmia (nanophthalmia) pedigree, which is the first genetically analyzed Chinese microphthalmia pedigree, we performed a whole-genome scan using 382 micro-satellite DNA markers after the exclusion of reported candidates associated with microphthalmia. Strong evidence indicated that microphthalmia in this family was mapped to an unreported new locus on chromosome 2q. A significantly positive two-point LOD score was obtained with a maximum 3.290 at a recombination fraction of 0.00 for marker D2S2265. Subsequent haplotype analysis and recombination data further confined the disease-causing gene to a 15-cM interval between D2S1890 and D2S347 on 2q11-14. Our results further underlined the degree of heterogeneity in microphthalmia from Chinese background and localized a novel gene which regulates eye embryogenesis.

In vivo imaging of transport and biocompatibility of single silver nanoparticles in early development of zebrafish embryos

Real-time study of the transport and biocompatibility of nanomaterials in early embryonic development at single-nanoparticle resolution can offer new knowledge about the delivery and effects of nanomaterials in vivo and provide new insights into molecular transport mechanisms in developing embryos. In this study, we directly characterized the transport of single silver nanoparticles into an in vivo model system (zebrafish embryos) and investigated their effects on early embryonic development at single-nanoparticle resolution in real time. We designed highly purified and stable (not aggregated and no photodecomposition) nanoparticles and developed single-nanoparticle optics and in vivo assays to enable the study. We found that single Ag nanoparticles (5-46 nm) are transported into and out of embryos through chorion pore canals (CPCs) and exhibit Brownian diffusion (not active transport), with the diffusion coefficient inside the chorionic space (3 x 10(-9) cm(2)/s) approximately 26 times lower than that in egg water (7.7 x 10(-8) cm(2)/s). In contrast, nanoparticles were trapped inside CPCs and the inner mass of the embryos, showing restricted diffusion. Individual Ag nanoparticles were observed inside embryos at each developmental stage and in normally developed, deformed, and dead zebrafish, showing that the biocompatibility and toxicity of Ag nanoparticles and types of abnormalities observed in zebrafish are highly dependent on the dose of Ag nanoparticles, with a critical concentration of 0.19 nM. Rates of passive diffusion and accumulation of nanoparticles in embryos are likely responsible for the dose-dependent abnormalities. Unlike other chemicals, single nanoparticles can be directly imaged inside developing embryos at nanometer spatial resolution, offering new opportunities to unravel the related pathways that lead to the abnormalities.

Have we achieved a unified model of photoreceptor cell fate specification in vertebrates?

How does a retinal progenitor choose to differentiate as a rod or a cone and, if it becomes a cone, which one of their different subtypes? The mechanisms of photoreceptor cell fate specification and differentiation have been extensively investigated in a variety of animal model systems, including human and non-human primates, rodents (mice and rats), chickens, frogs (Xenopus) and fish. It appears timely to discuss whether it is possible to synthesize the resulting information into a unified model applicable to all vertebrates. In this review we focus on several widely used experimental animal model systems to highlight differences in photoreceptor properties among species, the diversity of developmental strategies and solutions that vertebrates use to create retinas with photoreceptors that are adapted to the visual needs of their species, and the limitations of the methods currently available for the investigation of photoreceptor cell fate specification. Based on these considerations, we conclude that we are not yet ready to construct a unified model of photoreceptor cell fate specification in the developing vertebrate retina.

Molecular mechanisms of optic vesicle development: complexities, ambiguities and controversies

Optic vesicle formation, transformation into an optic cup and integration with neighboring tissues are essential for normal eye formation, and involve the coordinated occurrence of complex cellular and molecular events. Perhaps not surprisingly, these complex phenomena have provided fertile ground for controversial and even contradictory results and conclusions. After presenting an overview of current knowledge of optic vesicle development, we will address conceptual and methodological issues that complicate research in this field. This will be done through a review of the pertinent literature, as well as by drawing on our own experience, gathered through recent studies of both intra- and extra-cellular regulation of optic vesicle development and patterning. Finally, and without attempting to be exhaustive, we will point out some important aspects of optic vesicle development that have not yet received enough attention.

Skeletal elements in the vertebrate eye and adnexa: morphological and developmental perspectives

Although poorly appreciated, the vertebrate eye and adnexa are relatively common sites for skeletogenesis. In many taxa, the skeleton contributes to internal reinforcement in addition to the external housing of the eye (e.g., the circumorbital bones and eyelids). Eyeball elements such as scleral cartilage and scleral ossicles are present within a broad diversity of vertebrates, albeit not therian mammals, and have been used as important models for the study of condensations and epithelial-mesenchymal interactions. In contrast, other elements invested within the eye or its close surroundings remain largely unexplored. The onset and mode of development of these skeletal elements are often variable (early versus late; involving chondrogenesis, osteogenesis, or both), and most (if not all) of these elements appear to share a common neural crest origin. This review discusses the development and distribution of the skeletal elements within and associated with the developing eye and comments on homology of the elements where these are questionable.

Stable expression of intracellular Notch suppresses v-Src-induced transformation in avian neural cells

Understanding how disruption of differentiation contributes to the cancer cell phenotype is required to identify alterations essential for malignant transformation and provide experimental basis for their correction. We investigated whether primary quail neuroretina cells, transformed by a conditional v-Src mutant (QNR/v-src(ts)), could revert to a normal phenotype, in response to the stable expression of constitutively active Notch1 intracellular domain (ICN). This model system was chosen because Notch signaling plays an instructive role in cell fate determination during NR development, and because the intrinsic capacity of QNR cultures to differentiate is blocked by v-Src. We report that stable ICN expression results in suppression of QNR/v-src(ts) cell transformation in the presence of an active oncoprotein. This phenotypic reversion coincides with a major switch in cell identity, as these undifferentiated cells acquire glial differentiation traits. Both changes appear to be mediated by CBF, a transcription factor that binds to ICN and activates target genes. Cells restored to a normal and differentiated phenotype have undergone changes in the functioning of signaling effectors, essentially regulating cell morphology and cytoskeleton organization. This dominant interference may be partially mediated by an autocrine/paracrine mechanism, as revertant cells secrete a factor(s), which inhibits transformation properties of QNR/v-src(ts) cells.

Recapitulation of human betaB1-crystallin promoter activity in transgenic zebrafish

Development of the eye is morphologically similar among vertebrates, indicating that the underlying mechanism regulating the process may have been highly conserved during evolution. Herein we analyzed the promoter of the human betaB1-crytallin gene in zebrafish by transgenic experiments. To delineate the evolutionarily conserved regulatory elements, we performed serial deletion assays in the promoter region. The results demonstrated that the -90/+61-bp upstream proximal promoter region is sufficient to confer lens-tissue specificity to the human betaB1-crystallin gene in transgenic zebrafish. Through phylogenetic sequence comparisons and an electrophoretic mobility shift assay (EMSA), a highly conserved cis-element of a six-base pair sequence TG(A/C)TGA, the consensus sequence for the Maf protein binding site, within the proximal promoter region was revealed. Further, a site-mutational assay showed that this element is crucial for promoter activity. These data suggest that the fundamental transcriptional regulatory mechanism of the betaB1-crystallin gene has been well conserved between humans and zebrafish, and plausibly among all vertebrates, during evolution.

Expression patterns of Wnt genes during development of an anterior part of the chicken eye

To address the roles of Wnts in the development of the anterior eye, we used a chicken model to perform comprehensive expression analysis of all Wnt genes during anterior eye development. In analyzing the available genomic sequences, we found that the chicken genome encodes 18 Wnt proteins that are homologous to corresponding human and mouse proteins. The mRNA sequences for 12 chicken Wnt genes are available in GenBank, and mRNAs for six other Wnt genes (Wnt2, Wnt5b, Wnt7b, Wnt8b, Wnt9b, and Wnt16) were identified and cloned based on the homology to the genes from other species. In addition, we found that chicken Wnt3a and Wnt7b genes encode two alternative mRNA isoforms containing different first exons. Following in situ hybridization, we found that out of 18 Wnt genes, 11 genes were expressed in the anterior eye, exhibiting distinct temporal-spatial patterns. Several Wnts were expressed in the lens, including Wnt2 and Wnt2b in the anterior epithelium and Wnt5a, Wnt5b, Wnt7a, and Wnt7b in the differentiating lens fiber cells. In the cornea, we detected Wnt3a, Wnt6, and Wnt9b in the ocular surface ectoderm, including the corneal epithelium, and Wnt9a in the corneal endothelium from the onset of its differentiation. In the optic cup, Wnt2, Wnt2b, and Wnt9a were localized in the rim of the optic cup (presumptive iris), while Wnt5a and Wnt16 were detected in the ciliary epithelium/iris zone of the differentiated optic cup, and Wnt6 was expressed in the iridial mesenchyme. These data suggest that Wnt signaling might play important roles in anterior eye development.

Negative regulation of retinal-neurite extension by beta-catenin signaling pathway

Although there have been many studies on the regulation of neurite extension in mouse brain, such a mechanism in neural retina has remained to be clarified. To delineate the role of Wnt signaling in retinal development, we used a retrovirus-vector-mediated expression system to express various mutants forms of Wnt signaling members in E17.5 mouse retinal explant cultures, which are an excellent system to examine retinal development in vitro. Expression of constitutively active beta-catenin or Lef-1 in the retinal cells resulted in failure of neurite extension, suggesting that beta-catenin negatively regulates neurite extension in the retina through Lef-1 transcriptional activity. However, proliferation and differentiation of retinal cells into mature retinal cells such as rod-photoreceptor cells and Muller glia cells were not affected by perturbation of the Wnt-Lef-1 pathway. As in retinal cells, activation of beta-catenin-Lef-1 signaling inhibited NGF-induced neurite extension in PC12 cells without affecting their proliferation. Interestingly, the Wnt-Lef-1 signaling pathway suppressed neurite extension without affecting Mek-1 signal activity, which is known to promote neurite extension. We found that MAPK was activated in retinal explant cultures, but that perturbation of MAPK signals did not affect neurite extension. Taken together, our data suggest that the Wnt pathway functions in proper neurite extension by opposing positive signals for promotion of neurite extension that are distinct from those of the MAPK pathway.

Challenges in the study of neuronal differentiation: a view from the embryonic eye

Progress in the study of the molecular mechanisms that regulate neuronal differentiation has been quite impressive in recent years, and promises to continue to an equally fast pace. This should not lead us into a sense of complacency, however, because there are still significant barriers that cannot be overcome by simply conducting the same type of experiments that we have been performing thus far. This article will describe some of these challenges, while highlighting the conceptual and methodological breakthroughs that will be necessary to overcome them.

Lens and retina formation require expression of Pitx3 in Xenopus pre-lens ectoderm

Pitx3 is expressed in tissues fated to contribute to eye development, namely, neurula stage ectoderm and pre-chordal mesoderm, then presumptive lens ectoderm, placode, and finally lens. Pitx3 overexpression alters lens, optic cup, optic nerve, and diencephalon development. Many of the induced anomalies are attributable to midline deficits; however, as assessed by molecular markers, ectopic Pitx3 appears to temporarily enlarge the lens field. These changes are usually insufficient to generate either ectopic lenses to enlarge the eye that eventually differentiates. Conversely, use of a repressor chimera or of antisense morpholinos alters early expression of marker genes, and later inhibits lens development, thereby abrogating retinal induction. Reciprocal grafting experiments using wild-type and morpholino-treated tissues demonstrate that Pitx3 expression in the presumptive lens ectoderm is required for lens formation. Contradictory to recent assertions that retina can form in the absence of a lens, the expression of Pitx3 in the presumptive lens ectoderm is critical for retina development.

Roles of cell-intrinsic and microenvironmental factors in photoreceptor cell differentiation

Photoreceptor differentiation requires the coordinated expression of numerous genes. It is unknown whether those genes share common regulatory mechanisms or are independently regulated by distinct mechanisms. To distinguish between these scenarios, we have used in situ hybridization, RT-PCR, and real-time PCR to analyze the expression of visual pigments and other photoreceptor-specific genes during chick embryo retinal development in ovo, as well as in retinal cell cultures treated with molecules that regulate the expression of particular visual pigments. In ovo, onset of gene expression was asynchronous, becoming detectable at the time of photoreceptor generation (ED 5-8) for some photoreceptor genes, but only around the time of outer segment formation (ED 14-16) for others. Treatment of retinal cell cultures with activin, staurosporine, or CNTF selectively induced or down-regulated specific visual pigment genes, but many cognate rod- or cone-specific genes were not affected by the treatments. These results indicate that many photoreceptor genes are independently regulated during development, are consistent with the existence of at least two distinct stages of gene expression during photoreceptor differentiation, suggest that intrinsic, coordinated regulation of a cascade of gene expression triggered by a commitment to the photoreceptor fate is not a general mechanism of photoreceptor differentiation, and imply that using a single photoreceptor-specific "marker" as a proxy to identify photoreceptor cell fate is problematic.

Ocular coloboma: a reassessment in the age of molecular neuroscience

Congenital colobomata of the eye are important causes of childhood visual impairment and blindness. Ocular coloboma can be seen in isolation and in an impressive number of multisystem syndromes, where the eye phenotype is often seen in association with severe neurological or craniofacial anomalies or other systemic developmental defects. Several studies have shown that, in addition to inheritance, environmental influences may be causative factors. Through work to identify genes underlying inherited coloboma, significant inroads are being made into understanding the molecular events controlling closure of the optic fissure. In general, severity of disease can be linked to the temporal expression of the gene, but this is modified by factors such as tissue specificity of gene expression and genetic redundancy.

CHX10 targets a subset of photoreceptor genes

The homeobox gene CHX10 is required for retinal progenitor cell proliferation early in retinogenesis and subsequently for bipolar neuron differentiation. To clarify the molecular mechanisms employed by CHX10 we sought to identify its target genes. In a yeast one-hybrid assay Chx10 interacted with the Ret1 site of the photoreceptor-specific gene Rhodopsin. Gel shift assays using in vitro translated protein confirmed that CHX10 binds to Ret1, but not to the similar Rhodopsin sites Ret4 and BAT-1. Using retinal nuclear lysates, we observed interactions between Chx10 and additional photoreceptor-specific elements including the PCE-1 (Rod arrestin/S-antigen) and the Cone opsin locus control region (Red/green cone opsin). However, chromatin immunoprecipitation assays revealed that in vivo, Chx10 bound sites upstream of the Rod arrestin and Interphotoreceptor retinoid-binding protein genes but not Rhodopsin or Cone opsin. Thus, in a chromatin context, Chx10 associates with a specific subset of elements that it binds with comparable apparent affinity in vitro. Our data suggest that CHX10 may target these motifs to inhibit rod photoreceptor gene expression in bipolar cells.

Extraocular dorsal signal affects the developmental fate of the optic vesicle and patterns the optic neuroepithelium

Dorsal-ventral (DV) specification in the early optic vesicle plays a crucial role in the proper development of the eye. To address the questions of how DV specification is determined and how it affects fate determination of the optic vesicle, isolated optic vesicles were cultured either in vitro or in ovo. The dorsal and ventral halves of the optic vesicle were fated to develop into retinal pigment epithelium (RPE) and neural retina, respectively, when they were separated from each other and cultured. In optic vesicles treated with collagenase to remove the surrounding tissues, the neuroepithelium gave rise to cRax expression but not Mitf, suggesting that surrounding tissues are necessary for RPE specification. This was also confirmed in in ovo explant cultures. Combination cultures of collagenase-treated optic vesicles with either the dorsal or ventral part of the head indicated that head-derived factors have an important role in the fate determination of the optic vesicle: in the optic vesicles co-cultured with the dorsal part of the head Mitf expression was induced in the neuroepithelium, while the ventral head portion did not have this effect. The dorsal head also suppressed Pax2 expression in the optic vesicle. These observations indicate that factors from the dorsal head portion have important roles in the establishment of DV polarity within the optic vesicle, which in turn induces the patterning and differentiation of the neural retina and pigment epithelium.

Developmental expression patterns and localization of DNA-binding protein inhibitor (Id3) in the mouse retina

Id3 (inhibitor of DNA binding/differentiation), a member of the Id helix-loop-helix protein family, has long been studied as a positive regulator of proliferation and a negative regulator of differentiation. In this study, we examined the expression pattern and cellular phenotypes of Id3 in postnatal and adult mouse retina. Id3 was mainly expressed in the early postnatal inner retina. From the late postnatal development towards adulthood, Id3 expression was confined to the ganglion cell layer and the inner nuclear layer. Colocalization analysis showed that Id3 positive cells were identified as retinal ganglion cells and amacrine cells. The differential expression profiles of Id3 provide the groundwork for the elucidation of its possible role in retinal development.

Expression of Fgf19 in the developing chick eye

Fibroblast growth factor 19 (FGF19) is a new member of the FGF family of growth factors. Here, we describe the localization of Fgf19 mRNA in the developing chick retina and lens in stages from the Hamburger and Hamilton stage 15 (HH15) to postnatal day 30 (P30). Fgf19 was expressed in a transient manner in postmitotic neuroblasts during the migration from the ventricular surface to their final location. Moreover, from HH31 (embryonic day 7, E7) on, a subset of lined up Fgf19 expressing cells was distributed in the outer region of the presumptive INL. These cells were Pax6 immunoreactive horizontal cells. During the last third of embryogenesis, Fgf19 expression in the retina was progressively down-regulated and was not detected at P30. Also, it was transiently expressed in the equatorial region of the lens.

Adult retinal pigment epithelium cells express neural progenitor properties and the neuronal precursor protein doublecortin

The adult mammalian retina is devoid of any detectable neurogenesis. However, different cell types have been suggested to potentially act as neural progenitors in the adult mammalian retina in vitro, such as ciliary body (CB), Muller glia, and retinal pigment epithelium (RPE) cells. In rodents and humans, strong evidence for neural stem or progenitor properties exists only for CB-derived cells, but not for other retinal cell types. Here, we provide a comparative analysis of adult rat CB- and RPE-derived cells suggesting that the two cell types share certain neural progenitor properties in vitro. CB and RPE cells expressed neural progenitor markers such as Nestin, Flk-1, Hes1, and Musashi. They proliferated under adherent and neurosphere conditions and showed limited self-renewal. Moreover, they differentiated into neuronal and glial cells based on the expression of differentiation markers such as the young neuronal marker beta-III tubulin and the glial and progenitor markers GFAP and NG2. Expression of beta-III tubulin was found in cells with neuronal and non-neuronal morphology. A subpopulation of RPE- and CB-derived progenitor cells expressed the neurogenesis-specific protein doublecortin (DCX). Interestingly, DCX expression defined a beta-III tubulin-positive CB and RPE fraction with a distinct neuronal morphology. In summary, the data suggest that RPE cells share with CB cells the potential to de-differentiate into a cell type with neural progenitor-like identity. In addition, DCX expression might define the neuronal-differentiating RPE- and CB-derived progenitor population.

Natural antisense transcripts associated with genes involved in eye development

Natural antisense transcripts (NATs) are a class of genes whose role in controlling gene expression is becoming more and more relevant. We describe the identification of eight novel mouse NATs associated with transcription factors (Pax6, Pax2, Six3, Six6, Otx2, Crx, Rax and Vax2) that play an important role in eye development and function. These newly identified NATs overlap with the mature processed mRNAs or with the primary unprocessed transcript of their corresponding sense genes, are predicted to represent either protein coding or non-coding RNAs and undergo extensive alternative splicing. Expression studies, by both RT-PCR and RNA in situ hybridization, demonstrate that most of these NATs, similarly to their sense counterparts, display a specific or predominant expression in the retina, particularly at postnatal stages. We found a significant reduction of the expression levels of one of these NATs, Vax2OS (Vax2 opposite strand) in a mouse mutant carrying the inactivation of Vax2, the corresponding sense gene. In addition, we overexpressed another NAT, CrxOS, in mouse adult retina using adeno-associated viral vectors and we observed a significant decrease in the expression levels of the corresponding sense gene, Crx. These results suggest that these transcripts are functionally related to their sense counterparts and may play an important role in regulating the molecular mechanisms that underlie eye development and function in both physiological and pathological conditions.

Novel soluble molecule, Akhirin, is expressed in the embryonic chick eyes and exhibits heterophilic cell-adhesion activity

Akhirin, a novel secreted protein of 90 kDa, has been identified using signal sequence trap cDNA screening of an embryonic day 6 chicken lens cDNA library. Akhirin consists of one LCCL (Limulus factor C, Coch-5b2, and Lgl1) domain and two von Willebrand factor domains and displays high structural homology to vitrin and cochlin. The earliest expression of Akhirin is observed in the head ectoderm overlying the lens vesicle at stage 17 and in the retinal pigment epithelial layer at stage 22. It is persistently expressed in the ciliary marginal zone and in lens epithelium cells throughout embryonic eye development. Immunostaining with anti-Akhirin monoclonal antibody revealed a punctate distribution of Akhirin protein on living transfected cells. Cell adhesion and cell aggregation experiments showed that Akhirin has heterophilic cell-adhesion activity. Based on these observations, we hypothesize that Akhirin is involved in eye development.

Postnatal development of the eye in the naked mole rat (Heterocephalus glaber)

The naked mole rat (Heterocephalus glaber) is a subterranean rodent whose eyes are thought to be visually nonfunctional and as such is an ideal animal with which to pursue questions in evolutionary developmental biology. This report is the first in-depth study on the development and morphology of the naked mole rat eye. Using standard histological analysis and scanning and transmission electron microscopy, we describe the structural features of the eye. We further report on the morphological changes that accompany the development of this eye from neonate to adult and compare them with those that occur during mouse eye development. We observed numerous abnormalities in the shape and cellular arrangement of the structures of the anterior chamber, with notable malformations of the lens. Cell proliferation and cell death assays were conducted to investigate the possible causes of lens malformation. We found that neither of these processes appeared abnormal, indicating that they were not responsible for the lens phenotype of the mole rat. In order to investigate the process of lens differentiation, we analyzed the expression of gamma-crystallins using Western blots and immunocytochemistry. At birth, levels of gamma-crystallin appear normal, but soon thereafter, the gamma-crystallin expression is terminated. Absence of detectable gamma-crystallins in adults suggests that there is a gradual degradation and loss of these proteins. The evolutionary factors that could be responsible for the eye morphology of the naked mole rat are discussed. A model for abnormal lens differentiation and the role it plays in the morphogenesis of the rest of the eye in the naked mole rats is proposed.