MicroRNA Let-7a and dicer are important in the activation and implantation of delayed implanting mouse embryos

STUDY QUESTIONDoes Let-7a have a functional role in modulating dicer expression to activate dormant mouse blastocysts for implantation?SUMMARY ANSWERLet-7a post-transcriptionally regulates dicer expression altering microRNA expression to affect the implantation competency of the activated blastocysts.WHAT IS KNOWN ALREADYThe Let-7a microRNA is up-regulated during blastocyst dormancy and its forced-expression suppresses embryo implantation in vitro and in vivo. Dicer is a Let-7 target, which processes pre-microRNA to mature microRNA.STUDY DESIGN, SIZE, DURATIONThe effects on the expression of Let-7a and dicer in dormant blastocysts during the first 12 h after estradiol-induced activation, and the relationship between Let-7a and dicer in preimplantation embryos were determined. The effects on the microRNA expression and embryo implantation in vivo in dicer-knockdown mouse 5-8 cell embryos and dormant blastocysts at 1 h post estradiol activation were also studied.PARTICIPANTS/MATERIALS, SETTING, METHODSICR female mice at 6 weeks of age were ovariectomized on Day 4 of pregnancy to generate the delayed implantation model. Mouse 5-8 cell embryos and/or dormant blastocysts at 1 h after estradiol injection were electroporated with dicer siRNA and Let-7a precursor or Let-7a inhibitor. At 48 h post electroporation, the Let-7a expression, dicer transcripts and proteins in the embryos were determined using qPCR and immunostaining/western blotting, respectively. All experiments were repeated at least three times.MAIN RESULTS AND THE ROLE OF CHANCEEstradiol injection down-regulated Let-7a and up-regulated dicer in the dormant blastocysts during the first 12 h post-activation. Dicer knockdown at 1 h post-activation of blastocysts suppressed EGFR expression, attenuated EGF binding and compromised implantation of the transferred embryos. Let-7a transcriptionally regulated dicer by binding to the 3′-UTR of dicer in trophoblast cells. Dicer knockdown in blastocysts suppressed mature Let-7a expression and compromised implantation.LIMITATIONS, REASONS FOR CAUTIONGain- and loss-of-function approaches were used by analyzing transient expressions of transfected microRNA modulators or genes. The consequence of the Let-7a-dicer interaction on pregnancy remains to be determined. The study used the mouse as a model and the applicability of the observed phenomena in humans warrants further investigation.WIDER IMPLICATIONS OF THE FINDINGSOur results indicate that the Let-7a-dicer interaction leads to differential microRNA expression in dormant blastocysts after estradiol activation. Because the expression pattern of Let-7a in human blastocysts is similar to that in mouse blastocysts, our observation that the Let-7a-dicer interaction has a role in regulating the implantation potential of the mouse blastocysts could be applicable to humans.STUDY FUNDING/COMPETING INTEREST(S)This project is supported partly by a research grant from the Research Grant Council to W.S.B.Y. The authors have no competing interests to declare.