Developmental expression of the POU domain transcription factor Brn-3b (Pou4f2) in the lateral line and visual system...

Members of the class IV POU domain transcription factors are important regulators of neural development. In mouse, Brn-3b (Pou4f2, Brn3.2) and Brn-3c (Pou4f3, Brn3.1) are essential for the normal differentiation and maturation of retinal ganglion cells (RGCs) and hair cells of the auditory system, respectively. In this report, the cloning and expression profile of brn-3b in the zebrafish (Danio rerio) were assessed as the first step for understanding its role in the development of sensory systems. Two brn-3b alternative transcripts exhibited different onset of expression during development but shared overlapping expression domains in the adult visual system. The brn-3b expression in the zebrafish retina was consistent with a conserved role in differentiation and maintenance of RGCs. Expression was also observed in the optic tectum. Unexpectedly, brn-3b was prominently expressed in the migrating posterior lateral line primordium and larval neuromasts. For comparison, brn-3c expression was limited to the otic vesicle and was not detected in the lateral line during embryonic development. The expression of brn-3b in the mechanosensory lateral line of fish suggests a conserved function of a class IV POU domain transcription factor in sensory system development.