Sperm-Derived CircRNA-1572 Regulates Embryogenesis and Zygotic Genome Activation by Targeting CCNB2 via Bta-miR-2478-L-2.

Sperm non-coding RNAs, including micro RNAs, transfer RNA-derived small RNAs, and long non-coding RNAs, are pivotal in cellular cytoskeletal remodeling, early embryonic development, and offspring phenotypes. Despite the identification of circular RNAs (circRNAs) in mammals, the roles of sperm-derived circRNAs in embryogenesis remain largely unexplored. This study identify circRNA-1572, a sperm-derived circRNA deliver 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 confirm 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 led to reduce levels of CCNB2 mRNA and protein, along with altered fibrous actin (F-actin) distribution and aberrant chromosomal organization, leading to increase developmental arrest and impair zygotic genome activation (ZGA) during early porcine embryogenesis. Importantly, these phenotypes are rescued upon supplementary mRNA of CCNB2. Moreover, SMART-seq analysis reveals KD of CCNB2 resulted in delayed degradation of maternal transcripts in 2-cell embryos and delayed initiation of ZGA in 4-cell. This study provides novel insights into the molecular regulatory functions of sperm-derived circRNAs in early mammalian embryogenesis and underscores the impact of paternal factors on embryonic development.