Pou2, a class V POU-type transcription factor in zebrafish, regulates dorsoventral patterning and convergent extension movement at different blastula stages.

Abstract Zebrafish pou2 , which encodes a class V POU transcription factor considered to be an orthologue of mouse Oct-3/4, has been implicated by mutant analysis in dorsoventral (DV) patterning, gastrulation, and endoderm formation in early embryos and later in the regionalization of the neural plate. A series of gain-of-function experiments were conducted in the present study to directly reveal the roles pou2 plays in embryogenesis. We first revealed that injecting low-dose wild-type pou2 mRNA ventralizes embryos. Similar overexpression of activated ( vp- ) pou2 resulted in the same effects, whereas repressive ( en- ) pou2 caused dorsalization, supporting the previously proposed idea that pou2 is involved in DV patterning and that pou2 is a transcriptional activator. In contrast, high-dose mRNA for pou2 and its modified genes affected convergent extension (CE) movement. We observed similar activities for mouse Oct-3/4, suggesting conservation of the roles of this POU family in vertebrate development. To determine the critical stage for the functions of pou2 in embryos, we established a transgenic (Tg) fish line harboring en-pou2 under regulation of a heat-shock promoter ( HEP ) and found that the exposure of HEP Tg embryos to heat shock at the midblastula (sphere) stage dorsalized embryos, whereas induction of HEP at the late blastula stage (30–50% epiboly) affected CE movement. The defects due to HEP induction were rescued by introducing wild-type pou2 mRNA before the heat treatments. Collectively, these data demonstrated that pou2 regulates DV patterning and CE movement in zebrafish embryos at the midblastula and late blastula stages, respectively.