265 DICER GENE EXPRESSION IN PRE-IMPLANTATION MOUSE EMBRYOS: IMPLICATION OF TRANSCRIPTION REGULATION AT THE BLASTOCYST STAGE

Abstract

Dicer is an RNAse III enzyme that is related to the generation of the microRNAs involved in the gene silencing pathway. In order to obtain insight into the role of Dicer in early embryo development, we first evaluated its gene expression levels in mouse oocytes and embryos during in vitro development. The relative abundance of Dicer1 transcripts was established by real-time RT-PCR using the 2-ddCt method. H2a was applied as an internal standard to normalize the real-time RT-PCR reaction efficiency and quantify Dicer1 mRNA. Relatively high expression levels of mRNA in germinal vesicle-stage oocytes steadily decreased up to the 2-cell stage embryo, and then expression remained during morulae and blastocyst formation. Protein synthesis of Dicer was also observed in the mouse oocytes and early embryos. Specific silencing of mRNA expression and protein synthesis by RNA interference (siRNA) did not inhibit developmental events up to the blastocyst (BL) stage. However, Dicer1 siRNA reduced (P <0.05) total nuclei numbers in the BL-stage embryos (Dicer1: 77.2±4.2 vs. control: 62.7±3.1). Real-time RT-PCR also confirmed that, following Dicer1 siRNA microinjection into zygotes, transcription levels of several non-target genes, Cdc42, Cdh1, Dbc2, ILK, Tuba1, Plat, and Tie1, were not changed in blastocyst-stage embryos. However, selected transcription factors, Pou5f1 (P <0.01), Nanog (P <0.005), and Sox2 (P <0.01), in blastocysts were significantly down-regulated. Additionally, POU5F1 protein synthesis was also reduced. Using Applied Biosystem microarray technology, we compared gene expression profiles in control and Dicer1 siRNA microinjected blastocysts. This technique confirmed that 397 or 737 of 16354 genes were up- or down-regulated, respectively, following siRNA microinjection (P <0.05), including 52 transcription factors. The results suggest that expression of Dicer regulates gene expression at the blastocyst-stage embryo for cell fate, possibly by the transcription control.