Abstract
Maternal mRNA clearance is critical for the early embryo development, which is under the tight control of RNA N6-methyladenosine (m6A). However, little information is known regarding the maternal mRNA clearance and mechanisms behind it in farm animals. In the present study, 3362 differentially expressed genes (DEGs) were found during the maternal-to-zygotic transition (MZT) and determined as maternal mRNAs in goat. Of which, 1961 was decreased at the 4-cell stage embryos, while 1401 was trigged down-regulation at the 8-cell stage embryos, which were termed as maternally encoded mRNA decay genes and zygotic genome activation (ZGA)-dependent maternal mRNAs, respectively. The expression of m6A reader YTHDF2 was increased during goat ZGA, and knockdown of YTHDF2 resulted in decreased blastocyst rate. In the 8-cell stage YTHDF2 knockdown embryos, the M-decay and Z-decay maternal mRNA clearance were impaired. Specifically, the expression of deadenylase (CNOT1 and CNOT11) and decapping enzymes (DCP1A and DCP2) was decreased. In conclusion, we ascertained maternal mRNAs and inferred that maternal mRNA clearance is also ZGA-dependent in goat. We reported that YTHDF2 is vital for goat early embryogenesis as it advances maternal mRNA clearance, which might through the recruitment of deadenylases and mRNA decapping enzymes. This work will be of great value for understanding the stochastic reprogramming events during MZT and achieving better development of goat embryos in vitro.
Highlights
The early stages of embryogenesis in mammals takes place from the fertilization, during which, the majority of maternal mRNAs undergo rapid degradation and developmental control is handed from maternally provided gene products to those synthesized from the zygotic genome through a process known as maternal-to-zygotic transition (MZT)
Two replications were performed. Complementary DNA (cDNA) was fragmented by dsDNA fragmentase (NEB, M0348S) by incubating at 37◦C for 30 min, and size selection was performed with provided sample purification beads, the fragmented cDNA at the size of 150–300 bp was used for library construction
During the MZT process, there are 3113 transcripts in mice (Wu et al, 2016), 1434 genes in humans (Yan et al, 2013), and 2169 transcripts in bovine (Bogliotti et al, 2020) whose relative abundance decreased from MII to the zygotic genome activation (ZGA) stage, consistent with the notion that maternal mRNA degradation is evolutionarily conserved
Summary
The early stages of embryogenesis in mammals takes place from the fertilization, during which, the majority of maternal mRNAs undergo rapid degradation and developmental control is handed from maternally provided gene products to those synthesized from the zygotic genome through a process known as maternal-to-zygotic transition (MZT). Knockout of methyltransferase like 3 (METTL3), lysine-specific demethylase 5B (KDM5B), and lysine-specific demethylase 1A (LSD1) causes developmental arrest at the zygotic genome activation (ZGA) stage in mice (Ancelin et al, 2016; Dahl et al, 2016) and zebrafish (Xia et al, 2018) These and subsequent studies demonstrated that maternal gene products are essential for embryogenesis (Ancelin et al, 2016; Dahl et al, 2016; Xia et al, 2018; McDaniel et al, 2019). Developmental arrest was often observed during ZGA in embryos cultured in vitro, and increasing studies revealed that block of ZGA causes improper gene expression and embryonic lethality (Lee et al, 2014; Abe et al, 2018), suggesting that the onset of ZGA is pivotal for the early embryo development
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