N-methyladenosine (mA) is the most common internal modification in eukaryotic mRNA. It is dynamically installed and removed, and acts as a new layer of mRNA metabolism, regulating biological processes including stem cell pluripotency, cell differentiation, and energy homeostasis. mA is recognized by selective binding proteins; YTHDF1 and YTHDF3 work in concert to affect the translation of mA-containing mRNAs, YTHDF2 expedites mRNA decay, and YTHDC1 affects the nuclear processing of its targets. The biological function of YTHDC2, the final member of the YTH protein family, remains unknown. We report that YTHDC2 selectively binds mA at its consensus motif. YTHDC2 enhances the translation efficiency of its targets and also decreases their mRNA abundance. Ythdc2 knockout mice are infertile; males have significantly smaller testes and females have significantly smaller ovaries compared to those of littermates. The germ cells of Ythdc2 knockout mice do not develop past the zygotene stage and accordingly, Ythdc2 is upregulated in the testes as meiosis begins. Thus, YTHDC2 is an mA-binding protein that plays critical roles during spermatogenesis.
Transplantation of hematopoietic stem cells (HSCs) from human umbilical cord blood (hUCB) holds great promise for treating a broad spectrum of hematological disorders including cancer. However, the limited number of HSCs in a single hUCB unit restricts its widespread use. Although extensive efforts have led to multiple methods for ex vivo expansion of human HSCs by targeting single molecules or pathways, it remains unknown whether it is possible to simultaneously manipulate the large number of targets essential for stem cell self-renewal. Recent studies indicate that N-methyladenosine (mA) modulates the expression of a group of mRNAs critical for stem cell-fate determination by influencing their stability. Among several mA readers, YTHDF2 is recognized as promoting targeted mRNA decay. However, the physiological functions of YTHDF2 in adult stem cells are unknown. Here we show that following the conditional knockout (KO) of mouse Ythdf2 the numbers of functional HSC were increased without skewing lineage differentiation or leading to hematopoietic malignancies. Furthermore, knockdown (KD) of human YTHDF2 led to more than a 10-fold increase in the ex vivo expansion of hUCB HSCs, a fivefold increase in colony-forming units (CFUs), and more than an eightfold increase in functional hUCB HSCs in the secondary serial of a limiting dilution transplantation assay. Mapping of mA in RNAs from mouse hematopoietic stem and progenitor cells (HSPCs) as well as from hUCB HSCs revealed its enrichment in mRNAs encoding transcription factors critical for stem cell self-renewal. These mA-marked mRNAs were recognized by Ythdf2 and underwent decay. In Ythdf2 KO HSPCs and YTHDF2 KD hUCB HSCs, these mRNAs were stabilized, facilitating HSC expansion. Knocking down one of YTHDF2's key targets, Tal1 mRNA, partially rescued the phenotype. Our study provides the first demonstration of the function of YTHDF2 in adult stem cell maintenance and identifies its important role in regulating HSC ex vivo expansion by regulating the stability of multiple mRNAs critical for HSC self-renewal, thus identifying potential for future clinical applications.
Transfer RNA is heavily modified and plays a central role in protein synthesis and cellular functions. Here we demonstrate that ALKBH3 is a 1-methyladenosine (m1A) and 3-methylcytidine (m3C) demethylase of tRNA. ALKBH3 can promote cancer cell proliferation, migration and invasion. In vivo study confirms the regulation effects of ALKBH3 on growth of tumor xenograft. The m1A demethylated tRNA is more sensitive to angiogenin (ANG) cleavage, followed by generating tRNA-derived small RNAs (tDRs) around the anticodon regions. tDRs are conserved among species, which strengthen the ribosome assembly and prevent apoptosis triggered by cytochrome c (Cyt c). Our discovery opens a potential and novel paradigm of tRNA demethylase, which regulates biological functions via generation of tDRs.
N 6 -methyladenosine (m 6 A) on RNA and its regulatory components play critical roles in various developmental processes in mammals. However, the landscape and function of m 6 A in early embryos remain unclear due to limited materials. Current methods typically need total RNA greater than microgram amount to map m 6 A positions, which prevents us from revealing the crucial role of m 6 A in early embryonic development in mice. Here, we developed an ultra-low-input(ULI) MeRIP-seq method to reveal the transcriptome-wide m 6 A landscape in limited biological materials which contain as low as 50ng total RNA. Antibody-based ULI MeRIP-seq reveal the high e ciency of immunoprecipitation and reduced RNA loss during the experiments. Sequencing data reveal the m 6 A enrichment of mRNAs as well as noncoding RNAs which are highly recapitulated the results generated by 2µg of total RNA.To further promote the application on limited RNA materials, we describe a step-by-step protocol about how to construct a successful ULI MeRIP-seq library.
The nuclear exosome targeting (NEXT) complex is responsible for specific nuclear RNA degradation in mammalian cells. However, its function in development remains unknown. Here, we find that the depletion of a central factor of the NEXT complex, Zcchc8, in mouse results in developmental defects, a shortened lifespan, and infertility. We find that Zcchc8deficient embryonic stem cells (ESCs) exhibit proliferation abnormalities and reduced developmental potencies. Importantly, the transcripts of retrotransposon element LINE1 are found to be targeted by Zcchc8 and degraded by a Zcchc8-mediated mechanism. We further find that sustained expression of higher levels of LINE1 RNA is detected in maternal Zcchc8-depleted oocytes and embryos. Zcchc8depleted oocytes show higher chromatin accessibility and developmental defects in both meiotic maturation and embryogenesis after fertilization. Collectively, our study defines Zcchc8-mediated RNA degradation as an important post-transcription regulation of LINE1 transcripts in early embryos and ESCs, which play vital roles in the pluripotency and early development.
Objectives Accumulating evidences show that the regulatory network of m 6 A modification is essential for mammalian spermatogenesis. However, as an m 6 A reader, the roles of YTHDF2 remain enigmatic due to the lack of a proper model. Here, we employed the germ cell conditional knockout mouse model and explored the function of YTHDF2 in spermatogenesis. Materials and methods Ythdf2 germ cell conditional knockout mice were obtained by crossing Ythdf2 ‐floxed mice with Vasa ‐ Cre and Stra8 ‐ Cre mice. Haematoxylin and eosin (HE) staining, immunofluorescent staining and Western blotting were used for phenotyping. CASA, IVF and ICSI were applied for sperm function analysis. RNA‐seq, YTHDF2‐RIP‐seq and quantitative real‐time PCR were used to explore transcriptome changes and molecular mechanism analysis. Results Our results showed that YTHDF2 was highly expressed in spermatogenic cells. The germ cell conditional knockout males were sterile, and their sperm displayed malformation, impaired motility, and lost fertilization ability. During differentiated spermatogonia transiting to pachytene spermatocyte, most m 6 A‐modified YTHDF2 targets that were degraded in control germ cells persisted in pachytene spermatocytes of Ythdf2 ‐vKO mice. These delayed mRNAs were mainly enriched in pathways related to the regulation of transcription, and disturbed the transcriptome of round spermatid and elongated spermatid subsequently. Conclusion Our data demonstrate that YTHDF2 facilitates the timely turnover of phase‐specific transcripts to ensure the proper progression of spermatogenesis, which highlights a critical role of YTHDF2 in spermatogenesis.
METTL3 and METTL14 are two components that form the core heterodimer of the main RNA m 6A methyltransferase complex (MTC) that installs m 6A. Surprisingly, depletion of METTL3 or METTL14 displayed distinct effects on stemness maintenance of mouse embryonic stem cell (mESC). While comparable global hypo-methylation in RNA m 6A was observed in Mettl3 or Mettl14 knockout mESCs, respectively. Mettl14 knockout led to a globally decreased nascent RNA synthesis, whereas Mettl3 depletion resulted in transcription upregulation, suggesting that METTL14 might possess an m 6A-independent role in gene regulation. We found that METTL14 colocalizes with the repressive H3K27me3 modification. Mechanistically, METTL14, but not METTL3, binds H3K27me3 and recruits KDM6B to induce H3K27me3 demethylation independent of METTL3. Depletion of METTL14 thus led to a global increase in H3K27me3 level along with a global gene suppression. The effects of METTL14 on regulation of H3K27me3 is essential for the transition from self-renewal to differentiation of mESCs. This work reveals a regulatory mechanism on heterochromatin by METTL14 in a manner distinct from METTL3 and independently of m 6A, and critically impacts transcriptional regulation, stemness maintenance, and differentiation of mESCs.
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