Combinatorial expression of zebrafish Brn-1- and Brn-2-related POU genes in the embryonic brain, pronephric primordium, and pharyngeal arches

Vertebrate class III POU genes are widely expressed in the embryonic and ad ult central nervous system, where they act as transcriptional regulators of cell- and/or region-specific gene expression. We isolated four zebrafish c lass III POU genes, named zp-12, zp-23, zp-47 and zp-50. In this study, we examined the developmental expression patterns of the Brn-1- and Brn-2-rela ted zp-12, zp-23 and zp-47 genes by means of whole-mount in situ hybridizat ion. Similarly to their mammalian orthologues, the major expression site of all zebrafish zp genes is the CNS, Neurectodermal expression was first det ected at the beginning of somitogenesis in spatially restricted segment-lik e domains in different parts of the neural plate. During somitogenesis tran script distributions changed from highly restricted to widespread but never theless distinct patterns found in all major subdivisions of the CNS, While zp-47 expression was detected exclusively in the CNS, localized expression of zp-12 and zp-23 was also found in the pronephric primordium and in cell clusters within the mandibular and hyoid arches. Furthermore, zp-23 transc ripts were transiently detected in a restricted region of the paraxial mese ndoderm and, at late embryogenesis stages, in the auditory vesicles. The ea rly regionalized expression of all three zp genes is compatible with roles in regional specification of the neural plate. Comparison of the distinct y et overlapping expression of zp-12, zp-23, zp-47 and the previously charact erized zp-50 gene implies both unique, as well as redundant functions for e ach family member. We propose that coordinate expression of particular comb inations of class III POU genes contribute to pattern formation or cell fat e determination in the developing CNS and other structures. Dev Dyn 2000; 2 18:345-358. (C) 2000 Wiley Liss, Inc.