Abstract: MAP kinase phosphatase-2 (MKP-2/DUSP4), a dual specificity protein phosphatase with tyrosine/serine/ threonine phosphatase activity, is associated with cellular proliferation and differentiation, but its functions during embryo development are unclear. To study the developmental function of dusp4, we first examined the spatiotemporal ex-pression pattern of this gene during zebrafish embryonic development by whole mount in situ hybridization. We found that dusp4 was maternally expressed since its transcripts were present from the one-cell to the 256-cell stages. At early gastrulation stages, dusp4 transcripts specifically distributed at margin region, where the mesendodermal cells were located. Furthermore, Nodal signal was crucial for dusp4 expression. The expression of dusp4 was obviously increased in Nodal ligand overexpressed embryos, while its expression was almost lost in the Nodal sig-nal-deficient MZoep mutants. In addition, dusp4 MO was also designed to knock down its expression in embryos. The mesendoderm formation was significantly increased in dusp4 morphants, but not obviously changed in dusp4 overexpressed embryos, suggesting that dusp4 is necessary, but not sufficient for the inhibitory of mesendoderm induction. Thus, our results indicate that Nodal regulated dusp4 plays a repressive role in mesendoderm induction.

Key words: dusp4, Nodal, transcription regulation, mesendoderm