title: MicroRNA Let-7a and dicer are important in the activation and implantation of delayed implanting mouse embryos.
abstract: OBJECTIVE
  Does Let-7a have a functional role in modulating dicer expression to activate dormant mouse blastocysts for implantation?
  
  
  CONCLUSIONS
  Let-7a post-transcriptionally regulates dicer expression altering microRNA expression to affect the implantation competency of the activated blastocysts.
  
  
  BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
  
  
  CONCLUSIONS
  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.
  
  
  BACKGROUND
  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.
authors.affiliation: Department of Obstetrics and Gynaecology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, China.
authors.forename: Ana W Y
authors.initials: AW
authors.lastname: Cheong
authors.forename: Ronald T K
authors.initials: RT
authors.lastname: Pang
authors.forename: Wei-Min
authors.initials: WM
authors.lastname: Liu
authors.forename: Kottawattage Sanda Arunika
authors.initials: KS
authors.lastname: Kottawatta
authors.forename: Kai-Fai
authors.initials: KF
authors.lastname: Lee
authors.forename: William S B
authors.initials: WS
authors.lastname: Yeung
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000378:metabolism / Q000502:physiology; D002460:Cell Line; D053487:DEAD-box RNA Helicases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D010064:Embryo Implantation / Q000235:genetics*; D004624:Embryo Transfer; D004815:Epidermal Growth Factor / Q000378:metabolism; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D051379:Mice; D008813:Mice, Inbred ICR; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011247:Pregnancy; D034622:RNA Interference; D043244:Ribonuclease III / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D013997:Time Factors
chemical_list: D035683:MicroRNAs; C542687:mirnlet7 microRNA, mouse; D004958:Estradiol; D004815:Epidermal Growth Factor; C509781:Dicer1 protein, mouse; D043244:Ribonuclease III; D053487:DEAD-box RNA Helicases
keywords: dicer; dormant blastocyst; embryo implantation; estradiol activation; microRNA