Zygotic increase in microRNA-34c is required for the first cleavage division in mouse

Abstract

MicroRNAs (miRNAs) are small noncoding RNAs that regulate manybiological processes via gene silencing and/or transcript degradation.Their precise role(s) in preimplantation embryo developmentremains largely unclear. Here, we describe the miRNA expressionprofile of mouse preimplantation embryos by multiplex real-timepolymerase chain reaction and identify 16 miRNAs that are specificallyup-regulated in the zygotes. One of these miRNAs is miR-34c,which is weakly expressed in the oocytes but is increased by4-fold in the zygotes. Microinjection of miR-34c inhibitor,but not non-specific miRNA inhibitor in zygotes leads to aninhibition in DNA synthesis and significant suppression of thefirst cleavage division. 3'UTR luciferase assay and Westernblotting with or without inhibition of miR-34c showed that miR-34cregulates the expression of Bcl-2 in the zygotes and the trophoblastcell line JAR. Microinjection of anti-Bcl-2 antibody to zygotespartially reverses, while microinjection of Bcl-2 protein mimicsthe effect of miR-34c inhibition. In addition, microinjectionof either miR-34c inhibitor or Bcl-2 reduced c-myc expression,which is known to be important for early embryonic development.Our findings provides direct evidence that miR-34c is importantfor zygotic development and that Bcl-2 and c-myc are downstreammolecules of miR-34c modulating the first cleavage division.