Abnormal retinal development in Cloche mutant zebrafish

Background: Functions for the early embryonic vasculature in regulating development of central nervous system tissues, such as the retina, have been suggested by in vitro studies and by in vivo manipulations that caused additional ocular vessels to develop. Here, we use an avascular zebrafish embryo, cloche−/− (clo−/−), to begin to identify necessary developmental functions of the ocular vasculature in regulating development and patterning of the neural retina, in vivo. These studies are possible in zebrafish embryos, which do not yet rely upon the vasculature for tissue oxygenation. Results: clo−/− embryos lacked early ocular vasculature and were microphthalmic, with reduced retinal cell proliferation and cell survival. Retinas of clo mutants were disorganized, with irregular synaptic layers, mispatterned expression domains of retinal transcription factors, morphologically abnormal Müller glia, reduced differentiation of specific retinal cell types, and sporadically distributed cone photoreceptors. Blockade of p53‐mediated cell death did not completely rescue this phenotype and revealed ectopic cones in the inner nuclear layer. clo−/− embryos did not upregulate a molecular marker for hypoxia. Conclusions: The disorganized retinal phenotype of clo−/− embryos is consistent with a neural and glial developmental patterning role for the early ocular vasculature that is independent of its eventual function in gas exchange. Developmental Dynamics 244:1439–1455, 2015. © 2015 Wiley Periodicals, Inc. Key Findings The embryonic cloche‐/‐ eye lacks vasculature and displays numerous retinal defects. Retinal defects in cloche mutants include abnormal generation, patterning, and morphology of specific cell types. Retinal transcription factors show unusual patterns of expression in cloche mutants. The retinal defects in cloche‐/‐ embryos are not entirely related to cell death, or to retinal hypoxia, or to the complete lack of microglia, and they are not secondary to lens defects. These findings are consistent with a role for the early ocular vasculature in regulating retinal neurogenesis and patterning.