Sperm-derived circRNA-1572 regulates embryogenesis and zygotic genome activation by targeting CCNB2 via bta-miR-2478-L-2 [miRNA-seq]

This study identified circRNA-1572, which is delivered by sperm into the oocyte during fertilization, whose downregulation resulted in developmental arrest and inhibition of ZGA during porcine embryogenesis. Moreover, we elucidated that sperm-derived circRNA-1572 competitively binds to bta-miR-2478-L-2 through a “sponge” mechanism to target and regulate cyclin B2 expression, thereby modulating the distribution of F-actin in early pig embryos, ensuring proper chromosome segregation during mitosis, and facilitating normal embryo cleavage, maternal RNA degradation (MRD), and ZGA. This study identified circRNA-1572, a sperm-derived circRNA delivered into oocytes during fertilization, through whole-transcriptome sequencing of porcine metaphase II (MII) oocytes, purified mature sperm, and in vitro fertilized pronuclear (PN) embryos. Functional assays confirmed circRNA-1572 competitively binds to bta-miR-2478-L-2 through a “sponge” mechanism, regulating the expression of the target gene cyclin B2 (CCNB2). Knockdown (KD) of circRNA-1572 or overexpression of bta-miR-2478-L-2 resulted in reduced CCNB2 mRNA and protein levels, along with altered F-actin distribution and aberrant chromosomal organization, leading to increased developmental arrest and compromised zygotic genome activation (ZGA) during early porcine embryogenesis. Importantly, these phenotypes were rescued upon supplementary mRNA of CCNB2. Moreover, SMART-seq analysis revealed KD of CCNB2 resulted in delayed degradation of maternal transcripts in 2-cell embryos and delayed initiation of ZGA in 4-cell.