The maternal to zygotic transition (MZT) is a crucial process in the early development of almost all animals, during which maternal mRNAs are degraded and the zygotic genome is activated (Li et al., 2013). How maternal mRNAs are degraded is one of the long-standing questions in the field of developmental and reproductive biology. Recently, high-throughput sequencing and genetic studies have determined that the elimination of maternal mRNAs is accomplished by two modes: the first mode is dependent on maternally encoded transcripts, while the second mode relies on zygotic transcription (Yartseva and Giraldez, 2015). The first mode is well characterized in Drosophila, in which the maternally encoded RNA-binding proteins SMAUG and PUMILIO are important mediators of maternal mRNA clearance (Semotok et al., 2005; Gerber et al., 2006). The second mode is exemplified by zygotically transcribed miR-430 in zebrafish that directly targets and triggers the deadenylation and subsequent clearance of maternal mRNAs (Giraldez et al., 2006). Despite these encouraging findings in model animals of lower species, the mechanisms governing the selective maternal mRNA clearance are still largely unclear in mammals.