Identification of a novel splicing form of zebrafish p73 having a strong transcriptional activity

p73 is a transcriptional activator related to tumor suppressor p53 and regulates differentiation, cell-cycle arrest, and apoptosis. Recently, zebrafish p73 (zp73α) was isolated and shown to be required for zebrafish embryogenesis. In this study, we isolated a novel splicing-variant of zp73 mRNA, which was generated by the use of an alternative splicing acceptor site, and designated it as zp73θ. The zp73θ mRNA encoded a carboxy-terminal structure distinct from that of zp73α. Whereas the expression level of zp73θ mRNA was much lower than that of zp73α in zebrafish adult tissues, it was relatively high and fluctuated during embryogenesis. Using Saos-2 cells for a transient reporter assay, we found that zp73θ, but not zp73α, had strong transcriptional activity when the experiments were performed at 34°C. In addition, zp73θ had the ability to suppress the growth of Saos-2 cells and to cause the developmental defects in zebrafish. These data indicated that zp73θ could work as a transcriptional activator in zebrafish.