Active role of small non-coding RNAs derived from SINE/B1 retrotransposon during early mouse development.

Small RNAs derived from repetitive sequences appear to play essential roles in mammalian gametogenesis and early development. In this study we focused on the short interspersed nucleotide element B1 (SINE/B1) small RNAs, which were zygotically expressed in pre-implantation mouse embryos; and we investigated whether the SINE/B1 small RNAs played an active role in gene silencing during early mouse development. The results indicated that the level of silencing activity involving the SINE/B1 small RNAs as mediators was significantly reduced in Dicer-knockdown mouse embryos. In addition, when the SINE/B1 small RNAs were mapped to a full-length SINE/B1 sequence, phase-distribution of the small RNAs appeared, suggesting possible enzymatic involvement. Therefore, our present study suggested that the zygotically expressed SINE/B1 small RNAs in pre-implantation mouse embryos contain active small RNAs, which were presumably processed by Dicer and involved in gene silencing.