Micro RNA expression and regulation in the uterus during embryo implantation in rat

Embryo implantation is a complex initial step in establishment of a successful pregnancy. Many m RNA s have been shown to be differentially expressed in the rat uterus during embryo implantation. However, the expression profiles of micro RNA s (mi RNA s), a key post‐transcriptional regulator of gene expression, in the rat uterus between the pre‐receptive and receptive phases are still unknown. Here, an mi RNA microarray was used to examine differential expression of mi RNA s in the rat uterus between the pre‐receptive and receptive phases. Twenty‐eight mi RNA s were up‐regulated and 29 mi RNA s were down‐regulated at least twofold during the receptive phase in rat uterus; these results were confirmed by Northern blotting. miR ‐ 29a was only highly expressed in rat uterus during the implantation period, and activation of delayed implantation and artificial decidualization enhanced the miR ‐ 29a level. Further investigation revealed that both the pro‐apoptotic factor genes Bak1 and Bmf and the anti‐apoptotic factor gene Bcl ‐ w are targets of miR ‐ 29a . There was weak binding between miR ‐ 29a and the 3′ UTR of the anti‐apoptotic factor gene Mcl1 . Over‐expression of miR ‐ 29a inhibited the late apoptosis of endometrial stromal cells, which may be due to the stronger binding capacity between miR ‐ 29a and the 3′ UTR of pro‐apoptotic factors than that between miR ‐ 29a and the 3′ UTR of anti‐apoptotic factors. Collectively, miR ‐ 29a plays an important role during embryo implantation by regulating both pro‐apoptotic and anti‐apoptotic factors. miR ‐ 29a may predominantly bind pro‐apoptotic factors, leading to inhibition of cell apoptosis.