Lin28a Is Dormant, Functional, and Dispensable During Mouse Oocyte-to-Embryo Transition1

Abstract

The oocyte-to-embryo transition (OET) denotes transformation of a highly differentiated oocyte into totipotent blastomeres of the early mammalian embryo. OET depends exclusively on maternal RNAs and proteins accumulated during oocyte growth, which implies importance of post-transcriptional control of gene expression. OET includes replacement of abundant maternal microRNAs (miRNAs), enriched also in differentiated cells and exemplified by the Let-7 family, with embryonic miRNAs common in pluripotent stem cells (the miR-290 family in the mouse). Lin28a and its homolog Lin28b encode RNA-binding proteins, which interfere with Let-7 maturation and facilitate reprogramming of induced pluripotent stem cells. Both Lin28a and Lin28b transcripts are abundant in mouse oocytes. To test the role of maternal expression of Lin28a and Lin28b during oocyte-to-zygote reprogramming, we generated mice with oocyte-specific knockdown of both genes by using transgenic RNA interference. Lin28a and Lin28b are dispensable during oocyte growth because their knockdown has no effect on Let-7a levels in fully grown germinal vesicle (GV)-intact oocytes. Furthermore, transgenic females were fertile and produced healthy offspring, and their overall breeding performance was comparable to that of wild-type mice. At the same time, 2-cell embryos derived from transgenic females showed up-regulation of mature Let-7, suggesting that maternally provided LIN28A and LIN28B function during zygotic genome activation. Consistent with this conclusion is increased translation of Lin28a transcripts upon resumption of meiosis. Our data imply dual repression of Let-7 during OET in the mouse model, the selective suppression of Let-7 biogenesis by Lin28 homologs superimposed on previously reported global suppression of miRNA activity.

CLARITY reveals dynamics of ovarian follicular architecture and vasculature in three-dimensions

“…These animals showed reduction of VEGF expression under hypoxia and defects in gonadotropin stimulation of VEGF expression21. After genotyping of wild type and heterozygous animals (Fig.…”

Sculpting the Transcriptome During the Oocyte-to-Embryo Transition in Mouse

“…Other examples include the pluripotency factor LIN28, which regulates miRNA biogenesis during ZGA (Flemr, Moravec, Libova, Sedlacek, & Svoboda, 2014), as well as several mRNAs encoding E3 ubiquitin-protein ligases, which have the hallmark of a recruited maternal mRNA. E3 ligases recognize the targeted protein, catalyze the transfer of ubiquitin to that protein, and thereby provide specificity for selective protein degradation.…”

miRNA Control of Tissue Repair and Regeneration

“…8 The global suppression of miRNA during mouse oocyte-to-embryo transition is likely facilitated by the expression of highly conserved RNA binding proteins Lin28a and Lin28b that are abundant during embryogenesis. 9 Down-regulation of let-7 miRNA is initiated by the pluripotent factor Lin28 by onset of let-7 precursor (pre-let-7) uridylation using a noncanonical poly(A) polymerase, TUTase4 (TUT4). 10 These reports lead to the hypothesis that fetal tissue development is enabled by transiently silencing miRNA-dependent PTGS.…”