Specific and conserved roles of TAp73 during zebrafish development.

p53, p63 and p73 are related transcription factors involved in the regulation of cell proliferation, survival and differentiation. Here, we report the isolation and characterization of p73 from zebrafish. While for zebrafish p63 only N-terminally truncated isoforms (DeltaNp63) have been reported, p73 appears to be predominantly or exclusively present in transactivating isoforms (TAp73). p73 shows a very restricted expression pattern during zebrafish development. Transcripts are found in a subset of cells of the olfactory system, the telencephalon, the dorsal diencephalon, and the pronephric ducts. In addition, p73 is expressed in differentiating slow muscle cells of the somites, and in the pharyngeal endoderm. We carried out TAp73 gain- and loss-of-function experiments, injecting either TAp73alpha mRNA, or antisense morpholino oligonucleotides to suppress translation of TAp73 transcripts. The overexpression studies indicate that in contrast to p53, TAp73alpha has no pro-apoptotic effect in zebrafish embryos. However, TAp73 appears to be required for specific processes during the development of the olfactory system, the telencephalon and the pharyngeal arches. Together, our data point to both conserved and class-specific roles of p73 during vertebrate development.