Medaka eyeless is the key factor linking retinal determination and eye growth

European Molecular Biology Laboratory, Developmental Biology Programme, Meyerhofstr. 1, 69117 Heidelberg, Germany.
Development (Impact Factor: 6.46). 11/2001; 128(20):4035-44.
Source: PubMed


The complete absence of eyes in the medaka fish mutation eyeless is the result of defective optic vesicle evagination. We show that the eyeless mutation is caused by an intronic insertion in the Rx3 homeobox gene resulting in a transcriptional repression of the locus that is rescued by injection of plasmid DNA containing the wild-type locus. Functional analysis reveals that Six3- and Pax6- dependent retina determination does not require Rx3. However, gain- and loss-of-function phenotypes show that Rx3 is indispensable to initiate optic vesicle evagination and to control vesicle proliferation, by that regulating organ size. Thus, Rx3 acts at a key position coupling the determination with subsequent morphogenesis and differentiation of the developing eye.

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Available from: Sylke Winkler
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    • "Here we report, whole transcriptome sequencing of zebrafish rx3-/- eyeless mutants, a model of human anophthalmia [43]. Rx3 is a conserved transcription factor, whose orthologues are required for eye development in all vertebrates examined, including fish, frogs, mice and humans [2, 3, 9, 23, 44–46]. Here, we show that genes previously linked with microphthalmia, including aldh1a3, rx2, six6b, vsx2, and recently mab21l2 with anophthalmia [47], are constitutive elements of an Rx3-regulated gene network (Table  2, Figure  4). "
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    ABSTRACT: Background The genetic cascades underpinning vertebrate early eye morphogenesis are poorly understood. One gene family essential for eye morphogenesis encodes the retinal homeobox (Rx) transcription factors. Mutations in the human retinal homeobox gene (RAX) can lead to gross morphological phenotypes ranging from microphthalmia to anophthalmia. Zebrafish rx3 null mutants produce a similar striking eyeless phenotype with an associated expanded forebrain. Thus, we used zebrafish rx3-/- mutants as a model to uncover an Rx3-regulated gene network during early eye morphogenesis. Results Rx3-regulated genes were identified using whole transcriptomic sequencing (RNA-seq) of rx3-/- mutants and morphologically wild-type siblings during optic vesicle morphogenesis. A gene co-expression network was then constructed for the Rx3-regulated genes, identifying gene cross-talk during early eye development. Genes highly connected in the network are hub genes, which tend to exhibit higher expression changes between rx3-/- mutants and normal phenotype siblings. Hub genes down-regulated in rx3-/- mutants encompass homeodomain transcription factors and mediators of retinoid-signaling, both associated with eye development and known human eye disorders. In contrast, genes up-regulated in rx3-/- mutants are centered on Wnt signaling pathways, associated with brain development and disorders. The temporal expression pattern of Rx3-regulated genes was further profiled during early development from maternal stage until visual function is fully mature. Rx3-regulated genes exhibited synchronized expression patterns, and a transition of gene expression during the early segmentation stage when Rx3 was highly expressed. Furthermore, most of these deregulated genes are enriched with multiple RAX-binding motif sequences on the gene promoter. Conclusions Here, we assembled a comprehensive model of Rx3-regulated genes during early eye morphogenesis. Rx3 promotes optic vesicle morphogenesis and represses brain development through a highly correlated and modulated network, exhibiting repression of genes mediating Wnt signaling and concomitant enhanced expression of homeodomain transcription factors and retinoid-signaling genes. Electronic supplementary material The online version of this article (doi:10.1186/1471-2164-15-825) contains supplementary material, which is available to authorized users.
    Full-text · Article · Sep 2014 · BMC Genomics
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    • "The key factor marking the onset of retinal differentiation, and thereby the generation of retinal ganglion cells (RGCs) is the bHLH transcription factor , Atonal homolog seven (Atoh7, formerly Ath5) (Kay, 2005; Kay et al., 2001; Bassett and Wallace, 2012). Atoh7 is expressed in response to signals emanating from the optic stalk (Martinez-Morales et al., 2005; Masai et al., 2000) shortly after the expression of rx2 in RPCs of the central retina is declining (Loosli et al., 2001). A loss of function of atoh7 results in a complete loss of RGCs in zebrafish (Kay et al., 2001) and a massive reduction of RGCs in mouse (Le et al., 2006). "
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    ABSTRACT: During vertebrate eye development retinal progenitor cells (RPCs) differentiate into all neural cell types of the retina. Retinal ganglion cells (RGCs) represent the first cell type to be generated. For their development, Atoh7, a basic Helix Loop Helix (bHLH) transcription factor is crucial. Atoh7 loss of function results in a massive reduction or even a total loss of RGCs. However, inconsistent results have been obtained in atoh7 gain of function experiments with respect to ganglion cell genesis, implying that the effect of Atoh7 is likely to be dependent on the competence state of the RPC. In this study we addressed the differential susceptibilities of early RPCs to Atoh7 in vivo, using medaka. Unexpectedly, we observed a largely normal development of the dorsal retina, although atoh7 was precociously expressed. However, the development of the retina close to the optic nerve head (part of the ventral retina) was disturbed severely. Photoreceptors were largely absent and the Müller glia cell number was reduced significantly. The majority of cells in this domain were ganglion cells and the abnormal development of this area affected the closure of the optic fissure resulting in coloboma.
    Full-text · Article · Aug 2014 · Mechanisms of Development
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    • "The total lack of rx3 in chk zebrafish mutants leads to anophthalmic phenotypes (Kennedy et al., 2004) but rx3 may have multiple roles during the splitting of the eye field: it controls cell proliferation and the size of the optic vesicles (Loosli et al., 2001), modulates the convergence and lateral migration of retinal progenitors (Rembold et al., 2006), and controls retinal cell morphology (Medina-Martı´nez et al., 2009). During optic vesicle evagination, rx3 expressing cells are displaced laterally and rx3 expression is substituted by rx1. "
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    ABSTRACT: Ethanol has been described as a teratogen in vertebrate development. During early stages of brain formation, ethanol affects the evagination of the optic vesicles, resulting in synophthalmia or cyclopia, phenotypes where the optic vesicles partially or totally fuse. The mechanisms by which ethanol affects the morphogenesis of the optic vesicles are however largely unknown. In this study we make use of in situ hybridization, electron microscopy and immunohistochemistry to show that ethanol has profound effects on cell organization and gene expression during the evagination of the optic vesicles. Exposure to ethanol during early eye development alters the expression patterns of some genes known to be important for eye morphogenesis, such as rx3/1 and six3a. Furthermore, exposure to ethanol interferes with the acquisition of neuroepithelial features by the eye field cells, which is clear at ultrastructual level. Indeed, ethanol disrupts the acquisition of fusiform cellular shapes within the eye field. In addition, tight junctions do not form and retinal progenitors do not properly polarize, as suggested by the mis-localization and down-regulation of zo1. We also show that the ethanol-induced cyclopic phenotype is significantly different to that observed in cyclopic mutants, suggesting a complex effect of ethanol on a variety of targets. Our results show that ethanol not only disrupts the expression pattern of genes involved in retinal morphogenesis, such as rx3 and rx1, but also disrupts the changes in cell polarity that normally occur during eye field splitting. Thus, ethylic teratology seems to be related not only to modifications in gene expression and cell death but also to alterations in cell morphology.
    Full-text · Article · Jul 2013 · Neuroscience
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