Overlapping expression pattern of the IrxAa clustered genes (irx1a, irx2a, and irx4a) in zebrafish retina development. irx1a (A–D), irx2a (E–H), irx4a (I–L), and ath5 (M–P) expression in the GCL (ganglion cell layer) of the retina were revealed by the in situ hybridization of 24-, 30-, 36-, and 48-hpf embryos. The clustered irx genes are all expressed in differentiated GCL. irx1a expression is initiated in the retinal cells at 24 hpf (A) while irx2a expression is observed at 30 hpf (F and K, respectively). At 48 hpf, ath5, irx1a, irx2a, and irx4a are strongly expressed in the GCL. The asterisk (*) marks the choroid fissure of each embryo.
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