Zebrafish microRNA miR-430 promotes deadenylation and clearance of maternal mRNAs

MicroRNAs comprise 1-3% of all vertebrate genes, but their in vivo functions and mechanisms of action remain largely unknown. Zebrafish miR-430 is expressed at the onset of zygotic transcription and regulates morphogenesis during early development. Using a microarray approach and in vivo target validation, we find that miR-430 directly regulates several hundred target mRNAs. Targets are highly enriched for maternal mRNAs that accumulate in the absence of miR-430. We also show that miR-430 accelerates the deadenylation of target mRNAs. These results suggest that miR-430 facilitates the deadenylation and clearance of maternal mRNAs during early embryogenesis. Keywords: Dicer, MZdicer, miR-430, miRNA target, maternal, zygotic As a first step towards the identification of miR-430 targets, we compared the rate of mRNA degradation in wild type and maternal-zygotic (MZ) dicer mutant embryos, which are deficient in miRNA processing. We found that the rate of degradation of a target mRNA with partial complementarity to miR-430 is significantly reduced in MZdicer mutants. Providing miR-430 duplexes to MZdicer mutants restores the rate of target decay. These results indicate that miR-430 enhances the decay of target mRNAs. To identify miR-430 in vivo targets, we compared the mRNA expression profile of embryos that were wild-type, MZdicer, or MZdicer rescued with miR-430 (MZdicer+miR-430). This analysis identified ~600 genes that were upregulated in MZdicer, but not in MZdicer+miR-430. We have also analyzed the expression profile of the genes in the array at three different time points, one maternal stage(16 cell), and two Zygotic stages 5 hours and 9 hours