It is demonstrated that the RNA ac 4 C writer NAT10 is essential for the post-transcriptional regulation of mouse zygotic splicing activation and provide valuable view for further exploration of the epigenetic mechanism during maternal-to-zygotic transition.
Abstract
Programmed establishment of the zygote epitranscriptome orchestrates epitranscriptome fidelity and developmental potency acquisition during mammalian preimplantation embryogenesis. N4-acetylcytidine (ac
4
C) is a conserved RNA modification catalyzed by N-acetyltransferase 10 (NAT10), the currently established mammalian RNA ac
4
C writer, but its maternal function during the maternal-to-zygotic transition remains incompletely understood. In this study, we found that oocyte-specific
Nat10
ablation from primary follicle stage causes female infertility with embryonic developmental arrest predominantly at the 2-cell stage. Notably, the maternal protein NAT10 is essential for ac
4
C deposition on zygotic genome activation (ZGA) transcripts and maternal mRNAs, and the loss of
Nat10
can lead to abnormal accumulation of maternal transcripts and major ZGA inactivation. By interrogating ac
4
C LACE-seq, RNA-seq, and Ribo-lite data, we identify splicing-factor transcripts as prominent NAT10-associated ac
4
C targets whose mRNA abundance and ribosome occupancy are reduced after maternal
Nat10
deletion. These molecular changes are accompanied by impaired nuclear speckle organization and widespread disruption of detectable alternative-splicing events during zygotic splicing activation. Together, our findings demonstrate that the RNA ac
4
C writer NAT10 is essential for the post-transcriptional regulation of mouse zygotic splicing activation and provide valuable view for further exploration of the epigenetic mechanism during maternal-to-zygotic transition.
Chemical modifications of RNA molecules, collectively referred to as epitranscriptomics, have emerged as a critical layer of post-transcriptional gene regulation. Among these modifications, N6-methyladenosine (m6A) plays a key role in modulating RNA stability, localization, and translational efficiency without altering the underlying nucleotide sequence. In recent years, epitranscriptomics has been increasingly recognized for its involvement in mammalian reproductive processes. In mammalian oocytes, which undergo an extended period of transcriptional quiescence and rely predominantly on post-transcriptional regulation of maternally stored transcripts, RNA modifications are essential for proper gene expression control. During oocyte maturation and early pre-implantation embryo development, epitranscriptomic mechanisms ensure the timely turnover and translational regulation of maternal mRNAs, thereby supporting the correct execution of the maternal-to-zygotic transition. The proper accomplishment of these processes is crucial for the acquisition of developmental competence. Reversible RNA modifications therefore add an additional layer of complexity to the regulation of gene expression in oocytes and early embryos. This mini-review summarizes current knowledge on the role of m6A RNA methylation in mammalian oocyte developmental competence and early embryogenesis, highlighting recent experimental evidence and discussing potential implications for fertility and assisted reproductive technologies.
Chiara Cosseddu, S. Succu, F. Mossa et al.· Frontiers in Veterinary Scie...· 0 citations
Findings suggest that specific maternal RBPs may act as repressors that require precise degradation post-fertilization to relieve translational repression and ensure successful MZT.
Pinhua Wang, Siqi Wang, Haojie Yin et al.· Cellular and Molecular Life...· 0 citations
Eukaryotic RNA polymerase II transcripts carry a signature m7G cap (Cap0) structure that is co-transcriptionally added to the 5’ end, and is essential for translation and RNA stability. Higher eukaryotes carry additional essential ribose methylations on the first and second cap-proximal nucleotides, termed as Cap1 and Cap2, respectively. The ubiquitous Cap1 modification protects cellular RNAs from being recognized by the innate immune sensors. Cap2 is also implicated in such an innate immune role, but here we use our genetic analyses of two human cell lines and three mouse tissues to reveal that loss of CMTR2 does not result in activation of the innate immune response. Germline deletion of mouse CMTR2 shows that it is required for male and female fertility. While mutant germ cells proceed into the meiotic pachytene spermatocyte stage, their transcriptome fails to keep pace and transition from the preceding leptotene/zygotene stages. Such a meiotic role is not conserved in other vertebrates like zebrafish, as cmtr2 mutants are fertile, instead it has a role in defining sex, as all mutants are exclusively males. Taken together, our study reveals that CMTR2 does not influence innate immune response in human cells and mouse tissues, but shapes gene expression during developmental transitions.
Harsha Raheja, Elena Delfino, Michaela Dohnálková et al.· bioRxiv· 0 citations
It is found that CNOT1 was upregulated during mammalian ZGA, and that its knockdown led to developmental arrest and a marked reduction in blastocyst formation, which indicates that CNOT1 is a potential YTHDF2 target that orchestrates maternal mRNA decay and ZGA during goat embryogenesis.
The lack of temporal resolution in transcriptomic data during mammalian embryonic genome activation (EGA) has precluded the comprehensive understanding of the functional relationships between the various gene regulatory mechanisms governing this process. Here, we finely dissect the transcriptional dynamics of mouse EGA using precision in vitro fertilization (IVF) coupled with single-embryo RNA sequencing. Our highly temporally resolved dataset uncovers an extensive, step-wise remodeling of the embryonic messenger RNA landscape, affecting ∼30% of the total detectable transcripts over a 9-hour time frame. We capture the gradual shift from maternal to embryonic messenger RNAs, successfully identify ribosome biogenesis and translation as hallmarks of EGA, and find previously unidentified gene expression dynamics. We further uncover a set of eight histone demethylating enzymes among the earliest up-regulated EGA genes and leverage our precision-IVF to dissect the transcriptional versus developmental impact of histone H3 lysine-4 trimethylation (H3K4me3) remodeling after fertilization. Our results indicate that precocious removal of H3K4me3 from embryonic chromatin only modestly affects embryonic transcription without perturbing EGA timing, arguing against a major instructive role of precocious remodeling of maternally inherited H3K4me3 after fertilization on genome activation. High-resolution transcriptome mapping coupled with functional perturbations allows us to distinguish direct gene expression effects from general impacts on developmental timing, opening avenues for further quantitative characterization of the impact of epigenome remodeling on embryonic transcription.
Jasmina Al-Mousawi, L. Michetti, Laura Castaldi et al.· Science Advances· 0 citations
The maternal-to-zygotic transition (MZT) requires coordinated clearance and deadenylation of maternally deposited mRNAs, yet the underlying molecular mechanisms remain poorly understood. N6-methyladenosine (m6A) has emerged as a key regulator of maternal mRNA fate, but prior studies have relied on population-averaged short-read methods that cannot resolve modification state, poly(A) tail length, or isoform identity on the same molecule. Here, we employ nanopore direct RNA sequencing on zebrafish embryos across MZT to resolve the interplay between m6A deposition, mRNA clearance, and poly(A) tail length dynamics at single-molecule resolution. We find that 78% of expressed maternal genes harbor m6A-modified isoforms, significantly exceeding prior bulk estimates. Within-isoform comparisons demonstrate that m6A promotes mRNA decay, with CDS m6A contributing more to maternal mRNA clearance than 3’-UTR m6A. The positional context of m6A alone is sufficient to determine the temporal regulation of poly(A) tail lengths. CDS m6A constitutively suppresses tail length throughout MZT, while 3′-UTR m6A acquires shortening activity only after zygotic genome activation (ZGA). Transcriptomic analysis of ythdf2 knockout embryos reveals two unrecognized roles. Ythdf2 stabilizes m6A-marked maternal transcripts to set stoichiometry at MZT onset, and is also responsible for maintaining global poly(A) tail homeostasis prior to ZGA through an m6A-independent mechanism. Together, these findings define the single-molecule logic by which m6A modifications shape transcript fate during vertebrate MZT.
Sarah A. Alshawi, Anna Delgado-Tejedor, Srihari Madhavan et al.· bioRxiv· 0 citations
