Initiation of Parental Genome Reprogramming in Fertilized Oocyte by Splicing Kinase SRPK1-Catalyzed Protamine Phosphorylation

We performed ATAC-seq in mouse sperms and fertilized eggs with wild-type or P1 mutation (phosphorylation sites by SRPK1) to capture early genome reprogramming events ~5 hours post insemination. Surprisingly, we detected broadly distributed ATAC-seq reads across the mouse genome to paternal and maternal gametes formed with wild-type and single mutant sperm, and in contrast, we saw individual peaks with zygotes formed with the double mutant sperm. After assigning to paternal and maternal genomes, we found that the reads assignable to paternal genome was decreased with single and double mutants, compare with wild-type. Furthermore, we found the paternal genome in eggs fertilized with the double mutant sperm essentially retained all sperm-specific ATAC-seq peaks, which were also overlapped with the published H3.3 ChIP-seq signals on wild-type sperm, mostly corresponding to TSSs. Strikingly, the ATAC-seq signals on the maternal genome from eggs fertilized with the double mutant P1 sperm were literally identical to those in MII oocyte. Based on these data, we draw two important conclusions: (i) dramatic chromatin remodeling takes place in a highly coordinated fashion in both paternal and maternal pronuclei before they merge, and (ii) SRPK1-catalyzed protamine phosphorylation initiates such synchronized genome reprogramming in both gametes. Overall design: Mouse sperms were obtained from wild-type or knock-in male mice in the C57BL/6 background and MII oocytes were obtained from BALB/cJ female. Mouse fertilized eggs were harvested on 5 h after insemination. ATAC-seq was performed in these sperms and fertilized eggs.