title: The homeobox gene irx1a is required for the propagation of the neurogenic waves in the zebrafish retina.
abstract: Neurogenesis in the compound eyes of Drosophila and the camera eyes of vertebrates spreads in a wave-like fashion. In both phyla, waves of hedgehog expression are known to drive the wave of neuronal differentiation. The mechanism controlling the propagation of hedgehog expression during retinogenesis of the vertebrate eye is poorly understood. The Iroquois homeobox genes play important roles in Drosophila eye development; they are required for the up-regulation of hedgehog expression during propagation of the morphogenetic furrow. Here, we show that the zebrafish Iroquois homolog irx1a is expressed during retinogenesis and knockdown of irx1a results in a retinal phenotype strikingly similar to those of sonic hedgehog (shh) mutants. Analysis of shh-GFP transgene expression in irx1a knockdown retinas revealed that irx1a is required for the propagation of shh expression through the retina. Transplantation experiments illustrated that the effects of irx1a on shh expression are both cell-autonomous and non-cell-autonomous. Our results reveal a role for Iroquois genes in controlling hedgehog expression during vertebrate retinogenesis.
authors.affiliation: Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong, China.
authors.forename: Chi Wa
authors.initials: CW
authors.lastname: Cheng
authors.forename: Carol Hiu Mei
authors.initials: CH
authors.lastname: Yan
authors.forename: Chi-chung
authors.initials: CC
authors.lastname: Hui
authors.forename: Uwe
authors.initials: U
authors.lastname: Strähle
authors.forename: Shuk Han
authors.initials: SH
authors.lastname: Cheng
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D002454:Cell Differentiation; D005123:Eye / Q000196:embryology*; D005128:Eye Diseases / Q000235:genetics / Q000378:metabolism; D005346:Fibroblast Growth Factors / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D053823:Hedgehog Proteins / Q000235:genetics / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D012160:Retina / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D012165:Retinal Ganglion Cells / Q000378:metabolism*; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D053823:Hedgehog Proteins; D018398:Homeodomain Proteins; D014157:Transcription Factors; D029961:Zebrafish Proteins; C501593:irx1a protein, zebrafish; D005346:Fibroblast Growth Factors