UHRF1 phosphorylation by cyclin A2/cyclin-dependent kinase 2 is required for zebrafish embryogenesis

Ubiquitin-like, containing PHD and RING finger domains 1 (uhrf1) is regulated at the transcriptional level during the cell cycle and in developing zebrafish embryos. We identify phosphorylation as a novel means of regulating UHRF1 and demonstrate that Uhrf1 phosphorylation is required for gastrulation in zebrafish. Human UHRF1 contains a conserved cyclin dependent kinase 2 (CDK2) phosphorylation site at serine 661 that is phosphorylated in vitro by CDK2 partnered with Cyclin A2 (CCNA2), but not Cyclin E. A phosphoserine-661 specific antibody recognizes UHRF1 in both in mammalian cancer cells and in non-transformed zebrafish cells, but not in zebrafish bearing a mutation in ccna2. Depleting Uhrf1 from zebrafish embryos by morpholino injection causes arrest before gastrulation and early embryonic death. This phenotype is rescued by wild-type UHRF1, but not by UHRF1 in which the phospho-acceptor site is mutated, demonstrating that UHRF1 phosphorylation is essential for embryogenesis. UHRF1 was detected in the nucleus and cytoplasm, whereas non-phosphorylatable UHRF1 is unable to localize to the cytoplasm, suggesting the importance of localization in UHRF1 function. Together, these data point to an essential role for UHRF1 phosphorylation by CDK/CCNA2 during early vertebrate development.