In vertebrates,the embryonic body plan has been established during gastrulation.How microRNAs are involved in this process is largely unknown.Here we demonstrated that genetic deletion of miR-430 cluster causes developmental defects in cell movement,germ layer specification,axis patterning and organ progenitor formation in zebrafish.The miR-430 deficient embryos died around 5 days post fertilization,while injection of miR-430 mimics could rescue the lethal phenotype.Some rescued embryos could survive to adulthood,arguing for a crucial role for miR-430 during early development.Transcriptome analysis of early gastrula embryos indicated that many maternal transcripts are not properly degraded whereas some zygotic genes are not adequately activated in the miR-430 mutant.These data provide genetic evidence that miR-430 is required for establishment of embryonic body plan by properly clearance of the maternal transcripts and activation of zygotic genome during early embryonic development.