ketu mutant mice uncover an essential meiotic function for the ancient RNA helicase YTHDC2

The Role of N6-Methyladenosine in Mitochondrial Dysfunction and Pathology

Mitochondria are indispensable in cells and play crucial roles in maintaining cellular homeostasis, energy production, and regulating cell death. Mitochondrial dysfunction has various manifestations, causing different diseases by affecting the diverse functions of mitochondria in the body. Previous studies have mainly focused on mitochondrial-related diseases caused by nuclear gene mutations or mitochondrial gene mutations, or mitochondrial dysfunction resulting from epigenetic regulation, such as DNA and histone modification. In recent years, as a popular research area, m6A has been involved in a variety of important processes under physiological and pathological conditions. However, there are few summaries on how RNA methylation, especially m6A RNA methylation, affects mitochondrial function. Additionally, the role of m6A in pathology through influencing mitochondrial function may provide us with a new perspective on disease treatment. In this review, we summarize several manifestations of mitochondrial dysfunction and compile examples from recent years of how m6A affects mitochondrial function and its role in some diseases.

Intercellular bridges are essential for transposon repression and meiosis in the male germline

Germ cell connectivity via intercellular bridges is a widely conserved feature across metazoans. However, its functional significance is poorly understood. Intercellular bridges are essential for fertility in male mice as genetic ablation of a critical bridge component, TEX14, causes spermatogenic failure, but the underlying reasons are unknown. Here we utilized a Tex14 hypomorph with reduced intercellular bridges along with Tex14-null mice that completely lack bridges to examine the roles of germ cell connectivity during spermatogenesis. We report that in males deficient for TEX14 and intercellular bridges, germ cells fail to complete meiotic DNA replication, synapsis and meiotic double-strand break repair. They also derepress retrotransposons and accumulate retrotransposon-encoded proteins during meiosis. Single-cell RNA-sequencing confirms sharing of transcripts between wild-type spermatids and demonstrates its partial attenuation in Tex14 hypomorphs, indicating that intercellular bridges enable cytoplasmic exchange between connected germ cells in testes. Our findings suggest that regulation of meiosis is non-cell-intrinsic and inform a model in which intercellular bridges influence critical meiotic events and protect germline genome integrity during spermatogenesis.

Meioc-Piwil1 complexes regulate rRNA transcription for differentiation of spermatogonial stem cells

Ribosome biogenesis is vital for sustaining stem cell properties, yet its regulatory mechanisms are obscure. Herein, we show unique properties of zebrafish meioc mutants in which spermatogonial stem cells (SSCs) do not differentiate or upregulate rRNAs. Meioc colocalized with Piwil1 in perinuclear germ granules, but Meioc depletion resulted in Piwil1 accumulation in nucleoli. Nucleolar Piwil1 interacted with 45S pre-rRNA. piwil1 +/- spermatogonia with reduced Piwil1 upregulated rRNAs, and piwil1 +/- ;meioc -/- spermatogonia recovered differentiation later than those in meioc -/- . Further, Piwil1 interacted with Setdb1 and HP1α, and meioc -/- spermatogonia exhibited high levels of H3K9me3 and methylated CpG in the 45S-rDNA region. These results indicate that zebrafish SSCs maintain low levels of rRNA transcription with repressive marks similar to Drosophila piRNA targets of RNA polymerase II, and that Meioc has a unique function on preventing localization of Piwil1 in nucleoli to upregulate rRNA transcripts and to promote SSC differentiation.

Recent advances in methylation modifications of microRNA

microRNAs (miRNAs) are short single-stranded non-coding RNAs between 21 and 25 nt in length in eukaryotic organisms, which control post-transcriptional gene expression. Through complementary base pairing, miRNAs generally bind to their target messenger RNAs and repress protein production by destabilizing the messenger RNA and translational silencing. They regulate almost all life activities, such as cell proliferation, differentiation, apoptosis, tumorigenesis, and host-pathogen interactions. Methylation modification is the most common RNA modification in eukaryotes. miRNA methylation exists in different types, mainly N6-methyladenosine, 5-methylcytosine, and 7-methylguanine, which can change the expression level and biological mode of action of miRNAs and improve the activity of regulating gene expression in a very fine-tuned way with flexibility. In this review, we will summarize the recent findings concerning methylation modifications of miRNA, focusing on their biogenesis and the potential role of miRNA fate and functions.

The Roles of RNA N6-methyladenosine Modifications in Systemic Lupus Erythematosus

N6-methyladenosine (m6A) modification is the most widespread RNA internal modification involved in RNA metabolism. M6A regulators consist of writers, erasers and readers. They exert their function by methylation, demethylation and recognization respectively, participating in cell biology and immune responses. Previously, the focus of m6A modification is its effect on tumor progress. Currently, extensive m6A-related studies have been performed in autoimmune diseases, such as RA, IBD and SLE, revealing that the unique influence of m6A modification in autoimmunity is undeniable. In this review, we summarize the function of m6A regulators, analyze their roles in pathogenic immune cells, summarize the m6A modification in SLE, and provide the potential m6A-targeting therapies for autoimmune diseases.

Sperm RNA code in spermatogenesis and male infertility

Spermatozoa are traditionally thought to be transcriptionally inert, but recent studies have revealed the presence of sperm RNA, some of which is derived from the residues of spermatocyte transcription and some from epididymosomes. Paternal sperm RNA can be affected by external factors and further modified at the post-transcriptional level, for example N6-methyladenosine (m6A), thus shaping spermatogenesis and reproductive outcome. This review briefly introduces the origin of sperm RNA and, on this basis, summarizes the current knowledge on RNA modifications and their functional role in spermatogenesis and male infertility. The bottlenecks and knowledge gaps in the current research on RNA modification in male reproduction have also been indicated. Further investigations are needed to elucidate the functional consequences of these modifications, providing new therapeutic and preventive strategies for reproductive health and genetic inheritance.

YTHDC2 serves a distinct late role in spermatocytes during germ cell differentiation

Posttranscriptional regulation of gene expression by RNA-binding proteins can enhance the speed and robustness of cell state transitions by controlling RNA stability, localization, or if, when, or where mRNAs are translated. The RNA helicase YTHDC2 is required to shut down components of the mitotic program to facilitate a proper switch from mitosis to meiosis in mouse germ cells. Here, we show that YTHDC2 has a second essential role in promoting meiotic progression in late spermatocytes. Inducing conditional knockout of Ythdc2 during the first wave of spermatogenesis, after initiation of meiotic prophase, allowed YTHDC2-deficient germ cells to advance to the pachytene stage and properly express many meiotic markers. However, the YTHDC2-deficient spermatocytes mis-expressed a number of genes, some up-regulated and some down-regulated, failed to transition to the diplotene stage, and then quickly died. Coimmunoprecipitation experiments revealed that YTHDC2 interacts with several RNA-binding proteins in early or late spermatocytes, with many of the interacting proteins, including MEIOC, localizing to granules, similar to YTHDC2. Our findings suggest that YTHDC2 collaborates with other RNA granule components to facilitate proper progression of germ cells through multiple steps of meiosis via mechanisms influencing posttranscriptional regulation of RNAs.

Female-specific mechanisms of meiotic initiation and progression in mammalian oocyte development

Meiosis is regulated in sexually dimorphic manners in mammals. In females, the commitment to and entry into meiosis are coordinated with the developmental program of oocytes. Female germ cells initiate meiosis within a short time window during the fetal period and then undergo meiotic arrest until puberty. However, the genetic mechanisms underlying the orchestration of oocyte development and meiosis to maximize the reproductive lifespan of mammalian females remain largely elusive. While meiotic initiation is regulated by a sexually common mechanism, where meiosis initiator and Stimulated by Retinoic Acid Gene 8 (STRA8) activate the meiotic genes, the female-specific mode of meiotic initiation is mediated by the interaction between retinoblastoma (RB) and STRA8. This review highlights the female-specific mechanisms of meiotic initiation and meiotic prophase progression in the context of oocyte development. Furthermore, the downstream pathway of the RB-STRA8 interaction that may regulate meiotic arrest will be discussed in the context of oocyte development, highlighting a potential genetic link between the female-specific mode of meiotic entry and meiotic arrest.

Relevance, strategies, and added value of mouse models in androgenetics

BACKGROUND

Male Infertility is a prevalent condition worldwide, and a substantial fraction of cases are thought to have a genetic basis. Investigations into the responsible genes is limited experimentally, so mice have been used extensively to identify genes required for fertility and to understand their functions.

OBJECTIVES

To review the progress made in reproductive genetics based on experiments in mice, the impact upon clinical fertility genetics, and discuss how evolving technologies will continue to advance our understanding of human infertility genes.

RESULTS AND DISCUSSION

Gene knockout studies in mice have shown that several hundreds of genes are required for normal fertility and that this number is much higher in males than in females. In addition to gene discovery, the mouse is a powerful platform for functionally dissecting genetic pathways, modeling putative human infertility variants, identifying contraceptive targets, and developing in vitro gametogenesis.

CONCLUSION

These ongoing studies in mice have made an enormous contribution to our understanding of the genetics of human reproduction in the sense that the "parts list" of genes for mammalian gametogenesis is being elucidated. This would have been impossible to do in humans, and in vitro systems are not yet adequate to associate genes with andrological phenotypes, especially in the germline.

A homozygous missense variant in YTHDC2 induces azoospermia in two siblings

Male infertility is a complex multifactorial reproductive disorder with highly heterogeneous phenotypic presentations. Azoospermia is a medically non-manageable cause of male infertility affecting ∼1% of men. Precise etiology of azoospermia is not known in approximately three-fourth of the cases. To explore the genetic basis of azoospermia, we performed whole exome sequencing in two non-obstructive azoospermia affected siblings from a consanguineous Pakistani family. Bioinformatic filtering and segregation analysis of whole exome sequencing data resulted in the identification of a rare homozygous missense variant (c.962G>C, p. Arg321Thr) in YTHDC2, segregating with disease in the family. Structural analysis of the missense variant identified in our study and two previously reported functionally characterized missense changes (p. Glu332Gln and p. His327Arg) in mice showed that all these three variants may affect Mg2+ binding ability and helicase activity of YTHDC2. Collectively, our genetic analyses and experimental observations revealed that missense variant of YTHDC2 can induce azoospermia in humans. These findings indicate the important role of YTHDC2 deficiency for azoospermia and will provide important guidance for genetic counseling of male infertility.

The m6A regulators in prostate cancer: molecular basis and clinical perspective

Prostate cancer (PCa) is the second leading cause of cancer-related death among men in western countries. Evidence has indicated the significant role of the androgen receptor (AR) as the main driving factor in controlling the development of PCa, making androgen receptor inhibition (ARI) therapy a pivotal management approach. In addition, AR independent signaling pathways also contribute to PCa progression. One such signaling pathway that has garnered our attention is N6-Methyladenosine (m6A) signaling, which refers to a chemical modification on RNA with crucial roles in RNA metabolism and disease progression, including PCa. It is important to comprehensively summarize the role of each individual m6A regulator in PCa development and understand its interaction with AR signaling. This review aims to provide a thorough summary of the involvement of m6A regulators in PCa development, shedding light on their upstream and downstream signaling pathways. This summary sets the stage for a comprehensive review that would benefit the scientific community and clinical practice by enhancing our understanding of the biology of m6A regulators in the context of PCa.

Understanding the molecular mechanisms of human diseases: the benefits of fission yeasts

The role of model organisms such as yeasts in life science research is crucial. Although the baker's yeast (Saccharomyces cerevisiae) is the most popular model among yeasts, the contribution of the fission yeasts (Schizosaccharomyces) to life science is also indisputable. Since both types of yeasts share several thousands of common orthologous genes with humans, they provide a simple research platform to investigate many fundamental molecular mechanisms and functions, thereby contributing to the understanding of the background of human diseases. In this review, we would like to highlight the many advantages of fission yeasts over budding yeasts. The usefulness of fission yeasts in virus research is shown as an example, presenting the most important research results related to the Human Immunodeficiency Virus Type 1 (HIV-1) Vpr protein. Besides, the potential role of fission yeasts in the study of prion biology is also discussed. Furthermore, we are keen to promote the uprising model yeast Schizosaccharomyces japonicus, which is a dimorphic species in the fission yeast genus. We propose the hyphal growth of S. japonicus as an unusual opportunity as a model to study the invadopodia of human cancer cells since the two seemingly different cell types can be compared along fundamental features. Here we also collect the latest laboratory protocols and bioinformatics tools for the fission yeasts to highlight the many possibilities available to the research community. In addition, we present several limiting factors that everyone should be aware of when working with yeast models.

Roles of N6-methyladenosine writers, readers and erasers in the mammalian germline

N6-methyladenosine (m6A) is the most abundant internal modification of mRNAs in eukaryotes. Numerous studies have shown that m6A plays key roles in many biological and pathophysiological processes, including fertility. The factors involved in m6A-dependent mRNA regulation include writers, which deposit the m6A mark, erasers, which remove it, and readers, which bind to m6A-modified transcripts and mediate the regulation of mRNA fate. Many of these proteins are highly expressed in the germ cells of mammals, and some have been linked to fertility disorders in human patients. In this review, we summarise recent findings on the important roles played by proteins involved in m6A biology in mammalian gametogenesis and fertility. Continued study of the m6A pathway in the mammalian germline will shed further light on the importance of epitranscriptomics in reproduction and may lead to effective treatment of human fertility disorders.

The YTH domain-containing protein family: Emerging players in immunomodulation and tumour immunotherapy targets

BACKGROUND

The modification of N6-methyladenosine (m6A) plays a pivotal role in tumor by altering both innate and adaptive immune systems through various pathways, including the regulation of messenger RNA. The YTH domain protein family, acting as "readers" of m6A modifications, affects RNA splicing, stability, and immunogenicity, thereby playing essential roles in immune regulation and antitumor immunity. Despite their significance, the impact of the YTH domain protein family on tumor initiation and progression, as well as their involvement in tumor immune regulation and therapy, remains underexplored and lacks comprehensive review.

CONCLUSION

This review introduces the molecular characteristics of the YTH domain protein family and their physiological and pathological roles in biological behavior, emphasizing their mechanisms in regulating immune responses and antitumor immunity. Additionally, the review discusses the roles of the YTH domain protein family in immune-related diseases and tumor resistance, highlighting that abnormal expression or dysfunction of YTH proteins is closely linked to tumor resistance.

KEY POINTS

This review provides an in-depth understanding of the YTH domain protein family in immune regulation and antitumor immunity, suggesting new strategies and directions for immunotherapy of related diseases. These insights not only deepen our comprehension of m6A modifications and YTH protein functions but also pave the way for future research and clinical applications.

YTHDC2 serves a distinct late role in spermatocytes during germ cell differentiation

Post-transcriptional regulation of gene expression by RNA-binding proteins can enhance the speed and robustness of cell state transitions by controlling RNA stability, localization, or if, when or where mRNAs are translated. The RNA helicase YTHDC2 is required to shut down components of the mitotic program to facilitate a proper switch from mitosis to meiosis in mouse germ cells. Here we show that YTHDC2 has a second essential role in promoting meiotic progression in late spermatocytes. Inducing conditional knockout of Ythdc2 during the first wave of spermatogenesis, after initiation of meiotic prophase, allowed Ythdc2-deficient germ cells to advance to the pachytene stage and properly express many meiotic markers. However, the Ythdc2-deficient spermatocytes mis-expressed a number of genes, some up-regulated and some down-regulated, failed to transition to the diplotene stage, then quickly died. Co-immunoprecipitation experiments revealed that YTHDC2 interacts with several RNA-binding proteins in early or late spermatocytes, with many of the interacting proteins, including MEIOC, localizing to granules, similar to YTHDC2. Our findings suggest that YTHDC2 collaborates with other RNA granule components to facilitate proper progression of germ cells through multiple steps of meiosis via mechanisms influencing post-transcriptional regulation of RNAs.

Destabilization of mRNAs enhances competence to initiate meiosis in mouse spermatogenic cells

The specialized cell cycle of meiosis transforms diploid germ cells into haploid gametes. In mammals, diploid spermatogenic cells acquire the competence to initiate meiosis in response to retinoic acid. Previous mouse studies revealed that MEIOC interacts with RNA-binding proteins YTHDC2 and RBM46 to repress mitotic genes and to promote robust meiotic gene expression in spermatogenic cells that have initiated meiosis. Here, we have used the enhanced resolution of scRNA-seq and bulk RNA-seq of developmentally synchronized spermatogenesis to define how MEIOC molecularly supports early meiosis in spermatogenic cells. We demonstrate that MEIOC mediates transcriptomic changes before meiotic initiation, earlier than previously appreciated. MEIOC, acting with YTHDC2 and RBM46, destabilizes its mRNA targets, including the transcriptional repressors E2f6 and Mga, in mitotic spermatogonia. MEIOC thereby derepresses E2F6- and MGA-repressed genes, including Meiosin and other meiosis-associated genes. This confers on spermatogenic cells the molecular competence to, in response to retinoic acid, fully activate the transcriptional regulator STRA8-MEIOSIN, which is required for the meiotic G1/S phase transition and for meiotic gene expression. We conclude that, in mice, mRNA decay mediated by MEIOC-YTHDC2-RBM46 enhances the competence of spermatogenic cells to initiate meiosis.

Mechanisms of meiosis initiation and meiotic prophase progression during spermatogenesis

Meiosis is a critical step for spermatogenesis and oogenesis. Meiosis commences with pre-meiotic S phase that is subsequently followed by meiotic prophase. The meiotic prophase is characterized by the meiosis-specific chromosomal events such as chromosome recombination and homolog synapsis. Meiosis initiator (MEIOSIN) and stimulated by retinoic acid gene 8 (STRA8) initiate meiosis by activating the meiotic genes by installing the meiotic prophase program at pre-meiotic S phase. This review highlights the mechanisms of meiotic initiation and meiotic prophase progression from the point of the gene expression program and its relevance to infertility. Furthermore, upstream pathways that regulate meiotic initiation will be discussed in the context of spermatogenic development, indicating the sexual differences in the mode of meiotic entry.

The biological function of the N6-Methyladenosine reader YTHDC2 and its role in diseases

N6-methyladenosine (m6A) stands as the most prevalent modified form of RNA in eukaryotes, pivotal in various biological processes such as regulating RNA stability, translation, and transcription. All members within the YT521-B homology (YTH) gene family are categorized as m6A reading proteins, capable of identifying and binding m6A modifications on RNA, thereby regulating RNA metabolism and functioning across diverse physiological processes. YTH domain-containing 2 (YTHDC2), identified as the latest member of the YTH family, has only recently started to emerge for its biological function. Numerous studies have underscored the significance of YTHDC2 in human physiology, highlighting its involvement in both tumor progression and non-tumor diseases. Consequently, this review aims to further elucidate the pathological mechanisms of YTHDC2 by summarizing its functions and roles in tumors and other diseases, with a particular focus on its downstream molecular targets and signaling pathways.

Destabilization of mRNAs enhances competence to initiate meiosis in mouse spermatogenic cells

The specialized cell cycle of meiosis transforms diploid germ cells into haploid gametes. In mammals, diploid spermatogenic cells acquire the competence to initiate meiosis in response to retinoic acid. Previous mouse studies revealed that MEIOC interacts with RNA-binding proteins YTHDC2 and RBM46 to repress mitotic genes and promote robust meiotic gene expression in spermatogenic cells that have initiated meiosis. Here, we used the enhanced resolution of scRNA-seq, and bulk RNA-seq of developmentally synchronized spermatogenesis, to define how MEIOC molecularly supports early meiosis in spermatogenic cells. We demonstrate that MEIOC mediates transcriptomic changes before meiotic initiation, earlier than previously appreciated. MEIOC, acting with YTHDC2 and RBM46, destabilizes its mRNA targets, including transcriptional repressors E2f6 and Mga , in mitotic spermatogonia. MEIOC thereby derepresses E2F6- and MGA-repressed genes, including Meiosin and other meiosis-associated genes. This confers on spermatogenic cells the molecular competence to, in response to retinoic acid, fully activate transcriptional regulator STRA8-MEIOSIN, required for the meiotic G1/S phase transition and meiotic gene expression. We conclude that in mice, mRNA decay mediated by MEIOC-YTHDC2-RBM46 enhances the competence of spermatogenic cells to initiate meiosis.

SUMMARY STATEMENT

RNA-binding complex MEIOC-YTHDC2-RBM46 destabilizes its mRNA targets, including transcriptional repressors. This activity facilitates the retinoic acid-dependent activation of Meiosin gene expression and transition into meiosis.

RNA m6A methylation and regulatory proteins in pulmonary arterial hypertension

m6A (N6‑methyladenosine) is the most common and abundant apparent modification in mRNA of eukaryotes. The modification of m6A is regulated dynamically and reversibly by methyltransferase (writer), demethylase (eraser), and binding protein (reader). It plays a significant role in various processes of mRNA metabolism, including regulation of transcription, maturation, translation, degradation, and stability. Pulmonary arterial hypertension (PAH) is a malignant cardiopulmonary vascular disease characterized by abnormal proliferation of pulmonary artery smooth muscle cells. Despite the existence of several effective and targeted therapies, there is currently no cure for PAH and the prognosis remains poor. Recent studies have highlighted the crucial role of m6A modification in cardiovascular diseases. Investigating the role of RNA m6A methylation in PAH could provide valuable insights for drug development. This review aims to explore the mechanism and function of m6A in the pathogenesis of PAH and discuss the potential targeting of RNA m6A methylation modification as a treatment for PAH.

RNA modifications in cellular metabolism: implications for metabolism-targeted therapy and immunotherapy

Cellular metabolism is an intricate network satisfying bioenergetic and biosynthesis requirements of cells. Relevant studies have been constantly making inroads in our understanding of pathophysiology, and inspiring development of therapeutics. As a crucial component of epigenetics at post-transcription level, RNA modification significantly determines RNA fates, further affecting various biological processes and cellular phenotypes. To be noted, immunometabolism defines the metabolic alterations occur on immune cells in different stages and immunological contexts. In this review, we characterize the distribution features, modifying mechanisms and biological functions of 8 RNA modifications, including N6-methyladenosine (m6A), N6,2'-O-dimethyladenosine (m6Am), N1-methyladenosine (m1A), 5-methylcytosine (m5C), N4-acetylcytosine (ac4C), N7-methylguanosine (m7G), Pseudouridine (Ψ), adenosine-to-inosine (A-to-I) editing, which are relatively the most studied types. Then regulatory roles of these RNA modification on metabolism in diverse health and disease contexts are comprehensively described, categorized as glucose, lipid, amino acid, and mitochondrial metabolism. And we highlight the regulation of RNA modifications on immunometabolism, further influencing immune responses. Above all, we provide a thorough discussion about clinical implications of RNA modification in metabolism-targeted therapy and immunotherapy, progression of RNA modification-targeted agents, and its potential in RNA-targeted therapeutics. Eventually, we give legitimate perspectives for future researches in this field from methodological requirements, mechanistic insights, to therapeutic applications.

Identification and prediction of molecular subtypes of atherosclerosis based on m6A immune cell infiltration

BACKGROUND

Atherosclerosis is a complex disease with multiple molecular subtypes that are not yet fully understood. Recent studies have suggested that N6-methyladenosine (m6A) alterations may play a role in the pathogenesis of atherosclerosis. However, the relationship between m6A regulators and atherosclerosis remains unclear.

METHODS

In this study, we analyzed the expression levels of 25 m6A regulators in a cohort of atherosclerosis (AS) and non-AS patients using the R "limma" package. We also used machine learning models, including random forest (RF), support vector machine (SVM), generalized linear model (GLM), and extreme gradient boosting (XGB), to predict the molecular subtypes of atherosclerosis based on m6A immune cell infiltration.

RESULTS

We found that METTL3, YTHDF2, IGFBP1, and IGF2BP1 were overexpressed in AS patients compared to non-AS patients, while the other significant m6A regulators showed no significant difference. Our machine learning models achieved high accuracy in predicting the molecular subtypes of atherosclerosis based on m6A immune cell infiltration.

CONCLUSION

Our study suggests that m6A alterations may play a role in the pathogenesis of atherosclerosis, and that machine learning models can be used to predict molecular subtypes of atherosclerosis based on m6A immune cell infiltration. These findings may have important implications for the detection and management of atherosclerosis.

EGLN1: A Biomarker of Poor Prognosis of Cervical Cancer and a Target of Treatment

Objective: To conduct bioinformatics analysis on the prognostic effect, mechanism of action, and drug sensitivity of Egl-9 family hypoxia-inducible factor 1 (EGLN1) expression on cervical cancer. Methods: Bioinformatics were obtained from Gene Expression Profiling Interactive Analysis (GEPIA), Tumor Immune Estimation Resource (TIMER), and the human cancer metastasis database (HCMDB), and the effect of EGLN1 expression level on the prognosis of cervical cancer was comprehensively analyzed. The protein-protein interaction network was constructed by Search Tool for the Retrieval of Interacting Genes/Proteins (STRING), and the possible mechanism of EGLN1 affecting the prognosis of cervical cancer was discussed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. In addition, Gene Set Cancer Analysis (GSCALite) was used to predict sensitive drugs online. Results: The higher the expression level of EGLN1, the shorter the tumor-free survival time and overall survival time of cervical cancer. The higher the stage of cervical cancer, the higher the expression level of EGLN1. The expression of EGLN1 affects the degree of immune infiltration, the variation of somatic copy number, and the level of N6-methyladenosine (m6A) modification in cervical cancer. COX regression model suggested that EGLN1 was an independent prognostic factor of cervical cancer. Conclusions: The high expression of EGLN1 in cervical cancer is an independent risk factor for the prognosis of cervical cancer, which affects the prognosis of cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC) through different signal pathways. It is expected to be used to predict the sensitive anticancer drugs for the treatment of cervical cancer.

The role of m6A epigenetic modifications in tumor coding and non-coding RNA processing

BACKGROUND

Epigenetic modifications of RNA significantly contribute to the regulatory processes in tumors and have, thus, received considerable attention. The m6A modification, known as N6-methyladenosine, is the predominant epigenetic alteration found in both eukaryotic mRNAs and ncRNAs.

MAIN BODY

m6A methylation modifications are dynamically reversible and are catalyzed, removed, and recognized by the complex of m6A methyltransferase (MTases), m6A demethylase, and m6A methyl recognition proteins (MRPs). Published evidence suggests that dysregulated m6A modification results in abnormal biological behavior of mature mRNA, leading to a variety of abnormal physiological processes, with profound implications for tumor development in particular.

CONCLUSION

Abnormal RNA processing due to dysregulation of m6A modification plays an important role in tumor pathogenesis and potential mechanisms of action. In this review, we comprehensively explored the mechanisms by which m6A modification regulates mRNA and ncRNA processing, focusing on their roles in tumors, and aiming to understand the important regulatory function of m6A modification, a key RNA epigenetic modification, in tumor cells, with a view to providing theoretical support for tumor diagnosis and treatment. Video Abstract.

Do RNA modifications contribute to modulation of immune responses in allergic diseases?

RNA modifications have emerged as a fundamental mechanism of post-transcriptional gene regulation, playing vital roles in cellular physiology and the development of various diseases. While the investigation of RNA modifications has seen significant advancements, the exploration of their implication in allergic diseases has been comparatively overlooked. Allergic reactions, including hay fever, asthma, eczema and food allergies, result from hypersensitive immune responses, affecting a considerable population worldwide. Despite the high prevalence, the molecular mechanisms underlying these responses remain partially understood. The potential role of RNA modifications in modulating the hypersensitive immune responses has yet to be fully elucidated. This mini-review seeks to shed light on potential connections between RNA modifications and allergy, highlighting recent findings and potential future research directions. By expanding our understanding of the complex interplay between RNA modifications and allergic responses, we hope to unlock new avenues for allergy diagnosis, prognosis, and therapeutic intervention.

Role of histone lactylation interference RNA m6A modification and immune microenvironment homeostasis in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a severe disease resulting from progressive increases in pulmonary vascular resistance and pulmonary vascular remodeling, ultimately leading to right ventricular failure and even death. Hypoxia, inflammation, immune reactions, and epigenetic modifications all play significant contributory roles in the mechanism of PAH. Increasingly, epigenetic changes and their modifying factors involved in reprogramming through regulation of methylation or the immune microenvironment have been identified. Among them, histone lactylation is a new post-translational modification (PTM), which provides a novel visual angle on the functional mechanism of lactate and provides a promising diagnosis and treatment method for PAH. This review detailed introduces the function of lactate as an important molecule in PAH, and the effects of lactylation on N6-methyladenosine (m6A) and immune cells. It provides a new perspective to further explore the development of lactate regulation of pulmonary hypertension through histone lactylation modification.

Connecting the Dots: N6-Methyladenosine (m6 A) Modification in Spermatogenesis

N6-methyladenosine (m6 A) is the most common RNA modification found in eukaryotes and is involved in multiple biological processes, including neuronal development, tumorigenesis, and gametogenesis. It is well known that methylation-modifying enzymes (classified into writers, erasers, and readers) mediate catalysis, clearance, and recognition of m6 A. Recent studies suggest that these genes may be associated with spermatogenesis. Numerous studies have revealed the m6 A role during spermatogenesis. However, the expression patterns and relationships of these m6 A enzymes during various stages of spermatogenesis remain unknown. In this review, it is aimed to provide an overview of m6 A enzyme functions and elucidate their potential mechanisms and regulatory relationships at a specific phase during spermatogenesis, providing new insights into the m6 A modification underlying the spermatogenesis process.

ADAD2 interacts with RNF17 in P-bodies to repress the Ping-pong cycle in pachytene piRNA biogenesis

Pachytene piRNA biogenesis is a hallmark of the germline, distinct from another wave of pre-pachytene piRNA biogenesis with regard to the lack of a secondary amplification process known as the Ping-pong cycle. However, the underlying molecular mechanism and the venue for the suppression of the Ping-pong cycle remain elusive. Here, we showed that a testis-specific protein, ADAD2, interacts with a TDRD family member protein RNF17 and is associated with P-bodies. Importantly, ADAD2 directs RNF17 to repress Ping-pong activity in pachytene piRNA biogenesis. The P-body localization of RNF17 requires the intrinsically disordered domain of ADAD2. Deletion of Adad2 or Rnf17 causes the mislocalization of each other and subsequent Ping-pong activity derepression, secondary piRNAs overproduced, and disruption of P-body integrity at the meiotic stage, thereby leading to spermatogenesis arrested at the round spermatid stage. Collectively, by identifying the ADAD2-dependent mechanism, our study reveals a novel function of P-bodies in suppressing Ping-pong activity in pachytene piRNA biogenesis.

The N6-methyladenosine binding proteins YTH03/05/10 coordinately regulate rice plant height

N⁶-methyladenosine (m⁶A) is the most widely distributed and most abundant type of mRNA modification in eukaryotic. It provides a posttranscriptional level regulation of gene expression by regulating pre-mRNA splicing, mRNA degradation, or mRNA translational efficiency etc. The function of m⁶A modification is decoded by binding proteins that can specially bind to m⁶A. YT521-B homology (YTH) family proteins are the most important m⁶A-binding proteins in mammals and Arabidopsis. However, their roles in growth and development remain unknown. Here, we demonstrated that the YTH family proteins YTH03, YTH05 and YTH10 specifically bind to m⁶A-containing RNAs. Knockout of YTH03, YTH05 or YTH10 causes reduced plant height. Further research showed that simultaneously knockout of YTH03, YTH05 and YTH10 shows severe dwarf phenotype, suggesting these three genes regulate rice plant height in a functionally redundant manner. Additional transcriptome study showed that the reduced plant height of the yth03/05/10 triple mutant may be due to the blocked of diterpenoid and brassinolide synthesis pathway. Overall, we demonstrate that YTH03, YTH05 and YTH10 are all the m⁶A readers in rice and redundantly regulate rice plant height through the hormonal related pathway.

The m6A reader PRRC2A is essential for meiosis I completion during spermatogenesis

N6-methyladenosine (m6A) and its reader proteins YTHDC1, YTHDC2, and YTHDF2 have been shown to exert essential functions during spermatogenesis. However, much remains unknown about m6A regulation mechanisms and the functions of specific readers during the meiotic cell cycle. Here, we show that the m6A reader Proline rich coiled-coil 2A (PRRC2A) is essential for male fertility. Germ cell-specific knockout of Prrc2a causes XY asynapsis and impaired meiotic sex chromosome inactivation in late-prophase spermatocytes. Moreover, PRRC2A-null spermatocytes exhibit delayed metaphase entry, chromosome misalignment, and spindle disorganization at metaphase I and are finally arrested at this stage. Sequencing data reveal that PRRC2A decreases the RNA abundance or improves the translation efficiency of targeting transcripts. Specifically, PRRC2A recognizes spermatogonia-specific transcripts and downregulates their RNA abundance to maintain the spermatocyte expression pattern during the meiosis prophase. For genes involved in meiotic cell division, PRRC2A improves the translation efficiency of their transcripts. Further, co-immunoprecipitation data show that PRRC2A interacts with several proteins regulating mRNA metabolism or translation (YBX1, YBX2, PABPC1, FXR1, and EIF4G3). Our study reveals post-transcriptional functions of PRRC2A and demonstrates its critical role in the completion of meiosis I in spermatogenesis.

In vivo PIWI slicing in mouse testes deviates from rules established in vitro

Argonautes are small RNA-binding proteins, with some having small RNA-guided endonuclease (slicer) activity that cleaves target nucleic acids. One cardinal rule that is structurally defined is the inability of slicers to cleave target RNAs when nucleotide mismatches exist between the paired small RNA and the target at the cleavage site. Animal-specific PIWI clade Argonautes associate with PIWI-interacting RNAs (piRNAs) to silence transposable elements in the gonads, and this is essential for fertility. We previously demonstrated that purified endogenous mouse MIWI fails to cleave mismatched targets in vitro. Surprisingly, here we find using knock-in mouse models that target sites with cleavage-site mismatches at the 10th and 11th piRNA nucleotides are precisely sliced in vivo. This is identical to the slicing outcome in knock-in mice where targets are base-paired perfectly with the piRNA. Additionally, we find that pachytene piRNA-guided slicing in both these situations failed to initiate phased piRNA production from the specific target mRNA we studied. Instead, the two slicer cleavage fragments were retained in PIWI proteins as pre-piRNA and 17-19 nt by-product fragments. Our results indicate that PIWI slicing rules established in vitro are not respected in vivo, and that all targets of PIWI slicing are not substrates for piRNA biogenesis.

Overexpression of YTHDC2 contributes to the progression of prostate cancer and predicts poor outcomes in patients with prostate cancer

YTH domain-containing protein 2 (YTHDC2), a member of N6-methyladenosine (m6A) readers, has been reported to be closely associated with multiple cancer types. However, very little is known about the YTHDC2 gene and its involvement in prostate cancer. YTHDC2 protein expression level was analyzed and correlated to clinical outcomes in prostate cancer patients who underwent prostatectomy in Guizhou Provincial People's Hospital. The YTHDC2 expression level was also detected in prostate cancer cell lines and an immortalized prostate epithelial cell line BPH-1 and RWPE1 by quantitative real-time reverse transcription polymerase chain reaction. Furthermore, we established stable cell lines (DU145 and PC-3) transfected with either empty vector or the full-length YTHDC2 gene and conducted cell function assays in vitro. Fisher's exact test and Pearson χ² test were employed, Kaplan-Meier method was used for the survival analysis. Of 32 patient samples who enrolled in this study, YTHDC2 was significantly upregulated in prostate cancer (PCa) patients with higher Gleason scores and serum prostate-specific antigen levels. YTHDC2 expression was significantly elevated in all PCa cell lines compared to BPH-1 and RWPE1 (all p < 0.05). Functionally, the enforced expression of YTHDC2 markedly promoted cell growth, migration, and invasion efficacies in prostate cancer cells. Our data indicate that YTHDC2 upregulation may be potentially associated with the prognosis of prostate cancer patients.

N6-Methyladenosine RNA Modification in Normal and Malignant Hematopoiesis

Over 170 nucleotide variants have been discovered in messenger RNAs (mRNAs) and non-coding RNAs so far. However, only a few of them, including N6-methyladenosine (m6A), 5-methylcytidine (m5C), and N1-methyladenosine (m1A), could be mapped in the transcriptome. These RNA modifications appear to be dynamically regulated, with writer, eraser, and reader proteins being identified for each modification. As a result, there is a growing interest in studying their biological impacts on normal bioprocesses and tumorigenesis over the past few years. As the most abundant internal modification in eukaryotic mRNAs, m6A plays a vital role in the post-transcriptional regulation of mRNA fate via regulating almost all aspects of mRNA metabolism, including RNA splicing, nuclear export, RNA stability, and translation. Studies on mRNA m6A modification serve as a great example for exploring other modifications on mRNA. In this chapter, we will review recent advances in the study of biological functions and regulation of mRNA modifications, specifically m6A, in both normal hematopoiesis and malignant hematopoiesis. We will also discuss the potential of targeting mRNA modifications as a treatment for hematopoietic disorders.

YTHDC2 Promotes Malignant Phenotypes of Breast Cancer Cells

YTH domain-containing 2 (YTHDC2) is known to be an important regulator for RNA metabolism. Here, we show that YTHDC2 is essential for breast cancer tumorigenesis and metastasis. We examined YTHDC2 expression levels by immunohistochemistry in human breast tumor tissues from 99 patients and found a significantly positive correlation between the YTHDC2 expression level and the tumor stage. We established YTHDC2-knocked-down cell lines using four breast cancer cell lines with different subtypes. Knockdown of YTHDC2 attenuated the sphere-forming and the metastatic ability of breast cancer cells. Although stemness and EMT markers, such as SOX2, c-MYC, and NANOG, were downregulated in several YTHDC2-knocked-down breast cancer cells, a common target gene of YTHDC2 in breast cancer cells was not identified. These findings suggest that while YTHDC2 is involved in malignant progression of breast cancers, the mechanism by which YTHDC2 regulates those phenotypes is different between subtypes of breast cancers.

Targeting RNA N6-methyladenosine modification: a precise weapon in overcoming tumor immune escape

Immunotherapy, especially immune checkpoint inhibitors (ICIs), has revolutionized the treatment of many types of cancer, particularly advanced-stage cancers. Nevertheless, although a subset of patients experiences dramatic and long-term disease regression in response to ICIs, most patients do not benefit from these treatments. Some may even experience cancer progression. Immune escape by tumor cells may be a key reason for this low response rate. N⁶-methyladenosine (m⁶A) is the most common type of RNA methylation and has been recognized as a critical regulator of tumors and the immune system. Therefore, m⁶A modification and related regulators are promising targets for improving the efficacy of tumor immunotherapy. However, the association between m⁶A modification and tumor immune escape (TIE) has not been comprehensively summarized. Therefore, this review summarizes the existing knowledge regarding m⁶A modifications involved in TIE and their potential mechanisms of action. Moreover, we provide an overview of currently available agents targeting m⁶A regulators that have been tested for their elevated effects on TIE. This review establishes the association between m⁶A modifications and TIE and provides new insights and strategies for maximizing the efficacy of immunotherapy by specifically targeting m⁶A modifications involved in TIE.

The germ cell-specific RNA binding protein RBM46 is essential for spermatogonial differentiation in mice

Control over gene expression is exerted, in multiple stages of spermatogenesis, at the post-transcriptional level by RNA binding proteins (RBPs). We identify here an essential role in mammalian spermatogenesis and male fertility for 'RNA binding protein 46' (RBM46). A highly evolutionarily conserved gene, Rbm46 is also essential for fertility in both flies and fish. We found Rbm46 expression was restricted to the mouse germline, detectable in males in the cytoplasm of premeiotic spermatogonia and meiotic spermatocytes. To define its requirement for spermatogenesis, we generated Rbm46 knockout (KO, Rbm46-/-) mice; although male Rbm46-/- mice were viable and appeared grossly normal, they were infertile. Testes from adult Rbm46-/- mice were small, with seminiferous tubules containing only Sertoli cells and few undifferentiated spermatogonia. Using genome-wide unbiased high throughput assays RNA-seq and 'enhanced crosslinking immunoprecipitation' coupled with RNA-seq (eCLIP-seq), we discovered RBM46 could bind, via a U-rich conserved consensus sequence, to a cohort of mRNAs encoding proteins required for completion of differentiation and subsequent meiotic initiation. In summary, our studies support an essential role for RBM46 in regulating target mRNAs during spermatogonia differentiation prior to the commitment to meiosis in mice.

RNA binding protein RBM46 regulates mitotic-to-meiotic transition in spermatogenesis

Meiosis entry during spermatogenesis requires reprogramming from mitotic to meiotic gene expression profiles. Transcriptional regulation has been extensively studied in meiosis entry, but gain of function for master transcription factors is insufficient to down-regulate mitotic genes. RNA helicase YTHDC2 and its partner MEIOC emerge as essential posttranscriptional regulators of meiotic entry. However, it is unclear what governs the RNA binding specificity of YTHDC2/MEIOC. Here, we identified RNA binding protein RBM46 as a component of the YTHDC2/MEIOC complex. Testis-specific Rbm46 knockout in mice causes infertility with defective mitotic-to-meiotic transition, phenocopying global Ythdc2 or Meioc knockout. RBM46 binds to 3' UTR of mitotic transcripts within 100 nucleotides from YTHDC2 U-rich motifs and targets these transcripts for degradation. Dysregulated RBM46 expression is associated with human male fertility disorders. These findings establish the RBM46/YTHDC2/MEIOC complex as the major posttranscriptional regulator responsible for down-regulating mitotic transcripts during meiosis entry in mammalian spermatogenesis, with implications for understanding meiosis-related fertility disorders.

Physio-pathological effects of N6-methyladenosine and its therapeutic implications in leukemia

N6-methyladenosine (m6A), the most prevalent epigenetic modification of RNA in mammals, has become a hot topic throughout recent years. m6A is involved with every links of the RNA fate, including RNA splicing, nuclear export, translation and stability. Due to the reversible and dynamic regulatory network composed of ‘writers’ (methylase), ‘erasers’ (demethylase) and ‘readers’ (m6A binding proteins), m6A has been deemed as an essential modulator in vast physiological and pathological processes. Previous studies have shown that aberrant expression and dysfunction of these regulators are implicated in diverse tumors, exemplified by hematological malignancies. However, we should hold a dialectic perspective towards the influence of m6A modification on leukemogenesis. Given that m6A itself is neither pro-oncogenic nor anti-oncogenic, whether the modifications promote hematological homeostasis or malignancies occurrence and progression is dependent on the specific targets it regulates. Ample evidence supports the role of m6A in maintaining normal hematopoiesis and leukemogenesis, thereby highlighting the therapeutic potential of intervention in m6A modification process for battling leukemia. In this review, we introduce the advances of m6A modification and summarize the biological functions of m6A in RNA metabolism. Then we discuss the significance of several well-studied m6A regulators in modulating normal and malignant hematopoiesis, with focus on the therapeutic potentials of targeting these regulators for battling hematopoietic malignancies.

Multiple Roles of m6A RNA Modification in Translational Regulation in Cancer

Despite its discovery in the early 1970s, m⁶A modification within mRNA molecules has only powerfully entered the oncology field in recent years. This chemical modification can control all aspects of the maturation of mRNAs, both in the nucleus and in the cytoplasm. Thus, the alteration in expression levels of writers, erasers, and readers may significantly contribute to the alteration of gene expression observed in cancer. In particular, the activation of oncogenic pathways can lead to an alteration of the global rate of mRNA translation or the selective translation of specific mRNAs. In both cases, m⁶A can play an important role. In this review, we highlight the role of m⁶A in the regulation of translation by focusing on regulatory mechanisms and cancer-related functions of this novel but still controversial field.

One Stone, Two Birds: N6-Methyladenosine RNA Modification in Leukemia Stem Cells and the Tumor Immune Microenvironment in Acute Myeloid Leukemia

Acute myeloid leukemia is the most common acute leukemia in adults, with accumulation of abundant blasts and impairment of hematogenic function. Despite great advances in diagnosis and therapy, the overall survival of patients with acute myeloid leukemia remains poor. Leukemia stem cells are the root cause of relapse and chemoresistance in acute myeloid leukemia. The tumor immune microenvironment is another trigger to induce recurrence and drug resistance. Understanding the underlying factors influencing leukemia stem cells and the tumor immune microenvironment is an urgent and unmet need. Intriguingly, N6-methyladenosine, the most widespread internal mRNA modification in eukaryotes, is found to regulate both leukemia stem cells and the tumor immune microenvironment. Methyltransferases and demethylases cooperatively make N6-methyladenosine modification reversible and dynamic. Increasing evidence demonstrates that N6-methyladenosine modification extensively participates in tumorigenesis and progression in various cancers, including acute myeloid leukemia. In this review, we summarize the current progress in studies on the functions of N6-methyladenosine modification in acute myeloid leukemia, especially in leukemia stem cells and the tumor immune microenvironment. We generalize the landscape of N6-methyladenosine modification in self-renewal of leukemia stem cells and immune microenvironment regulation, as well as in the initiation, growth, proliferation, differentiation, and apoptosis of leukemia cells. In addition, we further explore the clinical application of N6-methyladenosine modification in diagnosis, prognostic stratification, and effect evaluation. Considering the roles of N6-methyladenosine modification in leukemia stem cells and the tumor immune microenvironment, we propose targeting N6-methyladenosine regulators as one stone to kill two birds for acute myeloid leukemia treatment.

Mechanism of initiation of meiosis in mouse germ cells

Meiosis is critical for germ cell development in multicellular organisms. Initiation of meiosis coincides with pre-meiotic S phase, which is followed by meiotic prophase, a prolonged G2 phase that ensures numerous meiosis-specific chromosome events. Meiotic prophase is accompanied by robust alterations of gene expression. In mouse germ cells, MEIOSIN and STRA8 direct cell cycle switch from mitosis to meiosis. MEIOSIN and STRA8 coordinate meiotic initiation with cell cycle, by activating the meiotic genes to have meiotic prophase program installed at S phase. This review mainly focuses on the mechanism of meiotic initiation in mouse germ cells from the viewpoint of the transcription of meiotic genes. Furthermore, signaling pathways that regulate meiotic initiation will be discussed in the context of germ cell development, pointing out the sexual differences in the mode of meiotic initiation.

The Progression of N6-methyladenosine Study and Its Role in Neuropsychiatric Disorders

Epitranscriptomic modifications can affect every aspect of RNA biology, including stability, transport, splicing, and translation, participate in global intracellular mRNA metabolism, and regulate gene expression and a variety of biological processes. N6-methyladenosine (m6A) as the most prevalent modification contributes to normal embryonic brain development and memory formation. However, changes in the level of m6A modification and the expression of its related proteins cause abnormal nervous system functions, including brain tissue development retardation, axon regeneration disorders, memory changes, and neural stem cell renewal and differentiation disorders. Recent studies have revealed that m6A modification and its related proteins play key roles in the development of various neuropsychiatric disorders, such as depression, Alzheimer’s disease, and Parkinson’s disease. In this review, we summarize the research progresses of the m6A modification regulation mechanism in the central nervous system and discuss the effects of gene expression regulation mediated by m6A modification on the biological functions of the neuropsychiatric disorders, thereby providing some insight into new research targets and treatment directions for human diseases.

The m6A methylation regulates gonadal sex differentiation in chicken embryo

Background

As a ubiquitous reversible epigenetic RNA modification, N6-methyladenosine (m6A) plays crucial regulatory roles in multiple biological pathways. However, its functional mechanisms in sex determination and differentiation during gonadal development of chicken embryos are not clear. Therefore, we established a transcriptome-wide m6A map in the female and male chicken left gonads of embryonic day 7 (E7) by methylated RNA immunoprecipitation sequencing (MeRIP-seq) to offer insight into the landscape of m6A methylation and investigate the post-transcriptional modification underlying gonadal differentiation.

Results

The chicken embryonic gonadal transcriptome was extensively methylated. We found 15,191 and 16,111 m6A peaks in the female and male left gonads, respectively, which were mainly enriched in the coding sequence (CDS) and stop codon. Among these m6A peaks, we identified that 1013 and 751 were hypermethylated in females and males, respectively. These differential peaks covered 281 and 327 genes, such as BMP2, SMAD2, SOX9 and CYP19A1, which were primarily associated with development, morphogenesis and sex differentiation by functional enrichment. Further analysis revealed that the m6A methylation level was positively correlated with gene expression abundance. Furthermore, we found that YTHDC2 could regulate the expression of sex-related genes, especially HEMGN and SOX9, in male mesonephros/gonad mingle cells, which was verified by in vitro experiments, suggesting a regulatory role of m6A methylation in chicken gonad differentiation.

Conclusions

This work provided a comprehensive m6A methylation profile of chicken embryonic gonads and revealed YTHDC2 as a key regulator responsible for sex differentiation. Our results contribute to a better understanding of epigenetic factors involved in chicken sex determination and differentiation and to promoting the future development of sex manipulation in poultry industry.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00710-6.

Domain confusion 2: m6A-independent role of YTHDC2

YTH proteins utilize YTH domains to interact with N6-methyladenines (m⁶A); however, Li et al. (2022) show that YTHDC2 binds U-rich motifs instead and functions independently of m⁶A through its unusual DExD helicase domain during spermatogenesis in mice and fish.

Profiling of Transcriptome-Wide N6-Methyladenosine (m6A) Modifications and Identifying m6A Associated Regulation in Sperm Tail Formation in Anopheles sinensis

Recent discoveries of reversible N6-methyladenosine (m6A) methylation on messenger RNA (mRNA) and mapping of m6A methylomes in many species have revealed potential regulatory functions of this RNA modification by m6A players—writers, readers, and erasers. Here, we first profile transcriptome-wide m6A in female and male Anopheles sinensis and reveal that m6A is also a highly conserved modification of mRNA in mosquitoes. Distinct from mammals and yeast but similar to Arabidopsis thaliana, m6A in An. sinensis is enriched not only around the stop codon and within 3′-untranslated regions but also around the start codon and 5′-UTR. Gene ontology analysis indicates the unique distribution pattern of m6A in An. sinensis is associated with mosquito sex-specific pathways such as tRNA wobble uridine modification and phospholipid-binding in females, and peptidoglycan catabolic process, exosome and signal recognition particle, endoplasmic reticulum targeting, and RNA helicase activity in males. The positive correlation between m6A deposition and mRNA abundance indicates that m6A can play a role in regulating gene expression in mosquitoes. Furthermore, many spermatogenesis-associated genes, especially those related to mature sperm flagellum formation, are positively modulated by m6A methylation. A transcriptional regulatory network of m6A in An. sinensis is first profiled in the present study, especially in spermatogenesis, which may provide a new clue for the control of this disease-transmitting vector.

Genetic Regulation of N6-Methyladenosine-RNA in Mammalian Gametogenesis and Embryonic Development

Emerging evidence shows that m⁶A is the most abundant modification in eukaryotic RNA molecules. It has only recently been found that this epigenetic modification plays an important role in many physiological and pathological processes, such as cell fate commitment, immune response, obesity, tumorigenesis, and relevant for the present review, gametogenesis. Notably the RNA metabolism process mediated by m⁶A is controlled and regulated by a series of proteins termed writers, readers and erasers that are highly expressed in germ cells and somatic cells of gonads. Here, we review and discuss the expression and the functional emerging roles of m⁶A in gametogenesis and early embryogenesis of mammals. Besides updated references about such new topics, readers might find in the present work inspiration and clues to elucidate epigenetic molecular mechanisms of reproductive dysfunction and perspectives for future research.

The XRN1-regulated RNA helicase activity of YTHDC2 ensures mouse fertility independently of m6A recognition

The functional consequence of N⁶-methyladenosine (m⁶A) RNA modification is mediated by "reader" proteins of the YTH family. YTH domain-containing 2 (YTHDC2) is essential for mammalian fertility, but its molecular function is poorly understood. Here, we identify U-rich motifs as binding sites of YTHDC2 on 3' UTRs of mouse testicular RNA targets. Although its YTH domain is an m⁶A-binder in vitro, the YTH point mutant mice are fertile. Significantly, the loss of its 3'→5' RNA helicase activity causes mouse infertility, with the catalytic-dead mutation being dominant negative. Biochemical studies reveal that the weak helicase activity of YTHDC2 is enhanced by its interaction with the 5'→3' exoribonuclease XRN1. Single-cell transcriptomics indicate that Ythdc2 mutant mitotic germ cells transition into meiosis but accumulate a transcriptome with mixed mitotic/meiotic identity that fail to progress further into meiosis. Finally, our demonstration that ythdc2 mutant zebrafish are infertile highlights its conserved role in animal germ cell development.

Pathogenic variants in the human m6A reader YTHDC2 are associated with primary ovarian insufficiency

Primary ovarian insufficiency (POI) affects 1% of women and carries significant medical and psychosocial sequelae. Approximately 10% of POI has a defined genetic cause, with most implicated genes relating to biological processes involved in early fetal ovary development and function. Recently, Ythdc2, an RNA helicase and N6-methyladenosine (m6a) reader, has emerged as a novel regulator of meiosis in mice. Here, we describe homozygous pathogenic variants in YTHDC2 in three women with early-onset POI from two families: c. 2567C>G, p.P856R in the helicase-associated (HA2) domain; and c.1129G>T, p.E377*. We demonstrate that YTHDC2 is expressed in the developing human fetal ovary and is upregulated in meiotic germ cells, together with related meiosis-associated factors. The p.P856R variant results in a less flexible protein that likely disrupts downstream conformational kinetics of the HA2 domain, whereas the p.E377* variant truncates the helicase core. Taken together, our results reveal that YTHDC2 is a key new regulator of meiosis in humans and pathogenic variants within this gene are associated with POI.

YTHDC2 control of gametogenesis requires helicase activity but not m6A binding

Mechanisms regulating meiotic progression in mammals are poorly understood. The N⁶-methyladenosine (m⁶A) reader and 3' → 5' RNA helicase YTHDC2 switches cells from mitotic to meiotic gene expression programs and is essential for meiotic entry, but how this critical cell fate change is accomplished is unknown. Here, we provide insight into its mechanism and implicate YTHDC2 in having a broad role in gene regulation during multiple meiotic stages. Unexpectedly, mutation of the m⁶A-binding pocket of YTHDC2 had no detectable effect on gametogenesis and mouse fertility, suggesting that YTHDC2 function is m⁶A-independent. Supporting this conclusion, CLIP data defined YTHDC2-binding sites on mRNA as U-rich and UG-rich motif-containing regions within 3' UTRs and coding sequences, distinct from the sites that contain m⁶A during spermatogenesis. Complete loss of YTHDC2 during meiotic entry did not substantially alter translation of its mRNA binding targets in whole-testis ribosome profiling assays but did modestly affect their steady-state levels. Mutation of the ATPase motif in the helicase domain of YTHDC2 did not affect meiotic entry, but it blocked meiotic prophase I progression, causing sterility. Our findings inform a model in which YTHDC2 binds transcripts independent of m⁶A status and regulates gene expression during multiple stages of meiosis by distinct mechanisms.

Protective role of m6A binding protein YTHDC2 on CCNB2 in manganese-induced spermatogenesis dysfunction

Human infertility has become the third largest serious disease in the world, seriously affecting the quality of human fertility. Studies have shown that manganese (Mn) can accumulate in the testis through the blood-testicular barrier and damage the male reproductive system. However, the mechanism has not been explored clearly. Recent studies have reported that YTH domain-containing 2 (YTHDC2) can regulate reproductive function. However, none has explored the role of YTHDC2 in Mn-induced reproductive toxicity. The present study investigated whether YTHDC2/CyclinB2 (CCNB2) pathway participates in Mn-induced reproductive toxicity using Kunming mice, spermatogonia, and the seminal plasma of male workers. The mice were received intraperitoneal (i.p.) injections of 0, 12.5, 25, and 50 mg/kg MnCl₂ once daily for 2 weeks. The cells were treated with 0, 100, 200 and 400 μM MnCl₂ for 24 h. Here, we found that occupational Mn exposure significantly increased Mn levels in the seminal plasma of male workers, while decreased sperm density, semen quality, and the levels of YTHDC2, CCNB1, and CCNB2. We found that Mn can inhibit the YTHDC2/CCNB2 signaling pathway and block the G2/M phase of the cell cycle. Moreover, the morphology of cells and the histomorphology of mice testis were injured. Notably, over-expression (OE) of YTHDC2 increased CCNB2 levels, reduced cell cycle arrest, and improved reproductive toxicity after Mn exposure. These findings suggest that the YTHDC2/CCNB2 signaling pathway participates in Mn-induced reproductive toxicity, and OE of YTHDC2 can mitigate the toxicity of Mn.