N6-Methyladenosine Sequencing Highlights the Involvement of mRNA Methylation in Oocyte Meiotic Maturation and Embryo Development by Regulating Translation in Xenopus laevis

Shu-Tao Qi,树涛 戚,Jun-Yu Ma,俊宇 马,Zhen-Bo Wang,震波 王,Lei Guo,磊 郭,Yi Hou,毅 侯,Qing-Yuan Sun,青原 孙

doi:10.1074/jbc.m116.748889

Shu-Tao Qi, 树涛戚 + Show 10 more

Open Access

https://doi.org/10.1074/jbc.m116.748889

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Abstract

During the oogenesis of Xenopus laevis, oocytes accumulate maternal materials for early embryo development. As the transcription activity of the oocyte is silenced at the fully grown stage and the global genome is reactivated only by the mid-blastula embryo stage, the translation of maternal mRNAs accumulated during oocyte growth should be accurately regulated. Previous evidence has illustrated that the poly(A) tail length and RNA binding elements mediate RNA translation regulation in the oocyte. Recently, RNA methylation has been found to exist in various systems. In this study, we sequenced the N6-methyladenosine (m6A) modified mRNAs in fully grown germinal vesicle-stage and metaphase II-stage oocytes. As a result, we identified 4207 mRNAs with m6A peaks in germinal vesicle-stage or metaphase II-stage oocytes. When we integrated the mRNA methylation data with transcriptome and proteome data, we found that the highly methylated mRNAs showed significantly lower protein levels than those of the hypomethylated mRNAs, although the RNA levels showed no significant difference. We also found that the hypomethylated mRNAs were mainly enriched in the cell cycle and translation pathways, whereas the highly methylated mRNAs were mainly associated with protein phosphorylation. Our results suggest that oocyte mRNA methylation can regulate cellular translation and cell division during oocyte meiotic maturation and early embryo development.

Highlights

These results suggest that coding DNA sequence (CDS) region RNA methylation may suppress mRNA translation
Previous evidence showed that oocyte mRNA translation is controlled by two mechanisms: poly(A) tail length-correlated translation efficiency and 3Ј UTR element-mediated mRNA translation activation
Evidence suggested a possible association of translation with RNA methylation [12, 16, 25], indicating that the 5Ј UTR m6A modification could initiate the translation of non-capped mRNAs

Summary

Results

M6A-Seq of GV- and MII-stage Oocytes in X. laevis—m6Amodified mRNAs of GV- and MII-stage oocytes from X. laevis (supplemental Fig. S1) were isolated and analyzed according to the methods described by Dominissini et al [18]. Compared with the highly methylated mRNAs, the hypomethylated RNAs showed significantly higher protein levels (Fig. 3; p values shown in supplemental Dataset S4). These results suggest that m6A modification may be associated with mRNA translation in oocytes or even in early embryos. MRNAs whose m6A modification occurred at the 3Ј UTR, in contrast, showed higher median protein levels (p values are shown in supplemental Dataset S4). These results suggest that CDS region RNA methylation may suppress mRNA translation. From the protein profile data calculated by Peshkin et al [23], we found that hypermethylated RNAs showed a lower protein synthesis rate (supplemental Fig. S5)

Discussion

Experimental Procedures