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

Hum Reprod. 2014 Apr;29(4):750-62. doi: 10.1093/humrep/det462. Epub 2014 Jan 12.


Study question: Does Let-7a have a functional role in modulating dicer expression to activate dormant mouse blastocysts for implantation?

Summary answer: Let-7a post-transcriptionally regulates dicer expression altering microRNA expression to affect the implantation competency of the activated blastocysts.

What is known already: The 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, duration: The 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, methods: ICR 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 chance: Estradiol 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 caution: Gain- 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 findings: Our 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.

Keywords: dicer; dormant blastocyst; embryo implantation; estradiol activation; microRNA.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blastocyst / metabolism
  • Blastocyst / physiology
  • Cell Line
  • DEAD-box RNA Helicases / antagonists & inhibitors
  • DEAD-box RNA Helicases / genetics
  • DEAD-box RNA Helicases / physiology*
  • Embryo Implantation / genetics*
  • Embryo Transfer
  • Epidermal Growth Factor / metabolism
  • Estradiol / pharmacology
  • Female
  • Gene Expression Regulation, Developmental
  • Humans
  • Mice
  • Mice, Inbred ICR
  • MicroRNAs / genetics
  • MicroRNAs / metabolism
  • MicroRNAs / physiology*
  • Pregnancy
  • RNA Interference
  • Ribonuclease III / antagonists & inhibitors
  • Ribonuclease III / genetics
  • Ribonuclease III / physiology*
  • Time Factors


  • MicroRNAs
  • mirnlet7 microRNA, mouse
  • Estradiol
  • Epidermal Growth Factor
  • Dicer1 protein, mouse
  • Ribonuclease III
  • DEAD-box RNA Helicases