Let-7 derived from endometrial extracellular vesicles is an important inducer of embryonic diapause in mice

Abstract

Embryonic diapause is a maternally controlled phenomenon. The molecule controlling the onset of the phenomenon is unknown. We demonstrated that overexpression of microRNA let-7a or incubation with let-7g–enriched extracellular vesicles from endometrial epithelial cells prolonged the in vitro survival of mouse blastocysts, which developed into live pups after having been transferred to foster mothers. Similar to in vivo dormant blastocysts, let-7–induced dormant blastocysts exhibited low level of proliferation, apoptosis, and nutrient metabolism. Let-7 suppressed c-myc/mTORC1 and mTORC2 signaling to induce embryonic diapause. It also inhibited ODC1 expression reducing biosynthesis of polyamines, which are known to reactivate dormant embryos. Furthermore, the overexpression of let-7 blocked trophoblast differentiation and implantation potential of human embryo surrogates, and prolonged survival of human blastocysts in vitro, supporting the idea that embryonic diapause was an evolutionary conserved phenomenon. In conclusion, let-7 is the main factor inducing embryonic diapause.

Placenta-Derived Exosomes as a Modulator in Maternal Immune Tolerance During Pregnancy

“…For example, endometrial epithelial cell-derived exosomes promote embryo attachment during implantation via miR-30d-dependent upregulation of integrins or through activation of focal adhesion kinase (FAK) signaling pathway ( 107 , 108 ). Another study shows that diapausing endometrial epithelial cell-derived exosomes enriched with miR-let-7 can protect the embryo from collapsing ( 109 ). Conversely, embryo-derived exosomes have been detected in spent embryo culture medium.…”

The Complicated Effects of Extracellular Vesicles and Their Cargos on Embryo Implantation

“…Let-7 is a major factor that induces diapause in embryos. Let-7-containing EVs from uterine fluid induce mouse embryonic diapause by inhibiting cmyc/mTORC1 and mTORC2 signaling pathways (73,74). Overexpression of EVs-derived let-7 potentially hamper trophoblast differentiation and the implantation capacity of embryo (73,74).…”

Molecular Regulation of Paused Pluripotency in Early Mammalian Embryos and Stem Cells

“…Exit from diapause is triggered by an increase in uterine receptivity that either occurs when lactation ends or can be experimentally induced by injection of estradiol. Mouse blastocysts can also be induced to enter a diapause-like paused state ex vivo via a few alternate methods for variable durations, including chemical inhibition of the cytoplasmic kinase mTOR (up to 30 days after blastocyst formation) (Bulut-Karslioglu et al, 2016), inhibition of the transcriptional regulator Myc (18 h) (Scognamiglio et al, 2016), and overexpression of the microRNA let-7 (up to 14 days) (Liu et al, 2020). These molecular regulators are further discussed below.…”

“…Nonetheless, qualitative evidence can be obtained. Indeed, Liu et al (2020) recently showed a slight delay in the development of human blastocysts upon treatment with extracellular vesicles carrying the microRNA let-7g (52% vs. 30% day 7 survival in treated vs. control embryos). Human blastocysts were also reported to undergo diapause when coated with a mucin-mimicking synthetic gel, however, these did not retain the characteristic blastocyst morphology (Canton et al, 2016).…”

“…In mice, fewer diapause embryos (Arena et al, 2021) and resulting fetuses (Weitlauf and Greenwald, 1968) are recovered with longer duration of diapause. Also, ex vivo survival of embryos in a diapause-like state diminishes over time (Bulut-Karslioglu et al, 2016;Liu et al, 2020). Metabolic restrictions, maternal or embryonic pathways may underlie diminishing embryo survival.…”