RNA‐methyltransferase Nsun5 controls the maternal‐to‐zygotic transition by regulating maternal mRNA stability

Abstract

Abstract Background RNA modification‐induced ovarian dysgenesis appears to be necessary for ovary development. However, how m5C (5‐methylcytosine)‐coordinating modificatory transcripts are dynamically regulated during oogenesis, and ovarian development is unknown. The purpose of this study was to determine whether NOP2/Sun RNA methyltransferase 5 (Nsun5) deletion leads to suppression of ovarian function and arrest of embryonic development. The regulation of mRNA decay and stability by m5C modification is essential at multiple stages during the maternal‐to‐zygotic (MZT) transition. Methods Mouse ovaries and oocytes with Nsun5KO and the KGN cell line were subjected to m5C identification, alternative splicing analysis and protein expression. BS‐m5C‐seq, real‐time polymerase chain reaction, Western blot, immunofluorescence and actinomycin D treatment assays were used. In particular, BS‐m5C‐seq revealed a dynamic pattern of m5C sites and genes in the ovaries between Nsun5KO and WT mice at the 2‐month and 6‐month stages. Diverse bioinformatic tools were employed to identify target genes for Nsun5. Results Here, a maternal mRNA stability study showed that deletion of the m5C methyltransferase Nsun5 obstructs follicular development and ovarian function, which leads directly to inhibition of embryogenesis and embryo development. Dynamic analysis of m5C revealed that the level of m5C decreased in a time‐dependent manner after Nsun5 knockout. Regarding the molecular mechanism, we found that Nsun5 deficiency caused a m5C decline in the exon and 3′UTR regions that influenced the translation efficiency of Mitotic arrest deficient 2 like 2 (MAD2L2) and Growth differentiation factor 9 (GDF9) in the ovary. Mechanistic investigation of alternative splicing indicated that Nsun5KO triggers aberrant events in the exon region of Brd8. Conclusions Nsun5 loss arrests follicular genesis and development in ovarian aging, indicating that Nsun5/m5C‐regulated maternal mRNA stabilization is essential for MZT transition.