Mettl3 Mutation Disrupts Gamete Maturation and Reduces Fertility in Zebrafish

Olfactory GnRH3 crypt sensory neurons transduce sex pheromone signals to induce male courtship behavior in zebrafish

Olfactory activation of neuroendocrine pathways plays vital roles in many organisms for reproduction and survival. The importance of gonadotropin-releasing hormone (GnRH) neurons for reproduction is well-established but little is known about whether they can directly sense and transmit sex pheromone signals. We have uncovered the migration path and distribution pattern of a new GnRH neuronal population that fulfills this role. GnRH3 neurons arise from the region located beneath olfactory placode, undergo bidirectional migration along the olfactory nerve, and cell bodies lie within the olfactory epithelium, olfactory bulb and hypothalamus. These olfactory epithelial GnRH3 neurons express ora4, the olfactory receptor that detects pheromones. GnRH3-OB neurons with olfactory epithelial GnRH3 neurons ablation failed to respond to the waterborne post-ovulatory sex pheromone prostaglandin F2α (PGF2α). GnRH3 neurons in gnrh3-/- mutants have a reduced basal firing rate leading to abnormal responses to PGF2α. Male gnrh3-/- zebrafish exhibit deficiencies in courtship behavior and a decreased capacity to compete and spawn with females. These findings indicate that GnRH3-OE neurons function as crypt sensory neurons transducing sex pheromone-encoded information critical to reproductive success.

The role of Chinese herbal medicine in diminished ovarian reserve management

Diminished Ovarian Reserve (DOR) is characterized by a reduction in the number of available follicles in the ovaries, leading to hormonal imbalances, decreased ovarian reserve, and reduced fertility. Clinically, it presents with elevated follicle-stimulating hormone (FSH) levels, decreased anti-Müllerian hormone (AMH) levels, and a lower antral follicle count (AFC). In recent years, Traditional Chinese Medicine (TCM) has gained recognition for its multi-target, holistic regulation in treating DOR, offering broad therapeutic effects with minimal side effects. This review aims to summarize the mechanisms and clinical efficacy of Chinese herbal medicine (CHM) formulas and active compounds in the treatment of DOR, providing theoretical support for their clinical application and future research. A systematic literature search was conducted from June 2019 to June 2024, and 12 clinical studies along with 38 basic research papers were selected. The findings suggest that CHM formulas primarily act by counteracting oxidative stress, regulating immune defense, modulating sex hormone secretion via the hypothalamic-pituitary-ovarian axis, and inhibiting excessive apoptosis of ovarian granulosa cells. This review highlights the therapeutic potential of TCM for improving ovarian function, regulating endocrine balance, and alleviating DOR symptoms, offering valuable insights for clinical practice and research.

Epigenetic regulation in oogenesis and fetal development: insights into m6A modifications

The unique physiological structure of women has led to a variety of diseases that have attracted the attention of many people in recent years. Disturbances in the reproductive system microenvironment lead to the progression of various female tumours and pregnancy disorders. Numerous studies have shown that epigenetic modifications crucially influence both oogenesis and foetal development. m6A, a modification at the mRNA level, consists of three parts, namely, writers, erasers, and readers, which are involved in several biological functions, such as the nucleation and stabilisation of mRNAs, thereby regulating the development of reproductive system diseases. In this manuscript, we delineate the constituents of m6A, their biological roles, and advancements in understanding m6A within the maternal-foetal immunological context. In addition, we summarise the mechanism of m6A in gynaecological diseases and provide a new perspective for targeting m6A to delay the progression of reproductive system diseases in clinical practice.

The roles of a MiRNA and its targeted methyltransferase 3 in carotenoid accumulation in adductor muscles of QN orange scallops

BACKGROUND

QN Orange scallops are interspecific hybrids with orange adductor muscles that are rich in carotenoids. In this study, analysis of miRNA expression profiles was performed to explore possible regulatory patterns involved in carotenoid accumulation in adductor muscles of QN Orange scallops.

RESULTS

A total of 91 differentially expressed miRNA between the white and orange adductor muscles were identified. GO and KEGG analysis of target genes of differentially expressed miRNAs revealed enrichments in the transmembrane transporter activity-related pathways, kinase activity-related pathways, signal transduction-related pathways, ATP binding cassette transporters (ABC transporters), retinol metabolism, lipid-related metabolism, and calcium signaling pathway. In particular, miRNA Contig1462_36180, which was shown to negatively regulate the activity of methyltransferase 3 (METTL3) by dual-luciferase reporter assay, may play a pivotal role in the accumulation of carotenoids. Furthermore, METTL3 interference seemed to reduce the pectenoxanthin content and m6A level.

CONCLUSION

It is thus speculated that Contig1462_36180 may regulate m6A methylation by regulating METTL3, which in turn affects pectenoxanthin accumulation in QN Orange scallops.

Epigenetic regulation in female reproduction: the impact of m6A on maternal-fetal health

With the development of public health, female diseases have become the focus of current concern. The unique reproductive anatomy of women leads to the development of gynecological diseases gradually become an important part of the socio-economic burden. Epigenetics plays an irreplaceable role in gynecologic diseases. As an important mRNA modification, m6A is involved in the maturation of ovum cells and maternal-fetal microenvironment. At present, researchers have found that m6A is involved in the regulation of gestational diabetes and other reproductive system diseases, but the specific mechanism is not clear. In this manuscript, we summarize the components of m6A, the biological function of m6A, the progression of m6A in the maternal-fetal microenvironment and a variety of gynecological diseases as well as the progression of targeted m6A treatment-related diseases, providing a new perspective for clinical treatment-related diseases.

The therapeutic potential of RNA m(6)A in lung cancer

Lung cancer (LC) is a highly malignant and metastatic form of cancer. The global incidence of and mortality from LC is steadily increasing; the mean 5-year overall survival (OS) rate for LC is less than 20%. This frustrating situation may be attributed to the fact that the pathogenesis of LC remains poorly understood and there is still no cure for mid to advanced LC. Methylation at the N6-position of adenosine (N6mA) of RNA (m(6)A) is widely present in human tissues and organs, and has been found to be necessary for cell development and maintenance of homeostasis. However, numerous basic and clinical studies have demonstrated that RNA m(6)A is deregulated in many human malignancies including LC. This can drive LC malignant characteristics such as proliferation, stemness, invasion, epithelial-mesenchymal transition (EMT), metastasis, and therapeutic resistance. Intriguingly, an increasing number of studies have also shown that eliminating RNA m(6)A dysfunction can exert significant anti-cancer effects on LC such as suppression of cell proliferation and viability, induction of cell death, and reversal of treatment insensitivity. The current review comprehensively discusses the therapeutic potential of RNA m(6)A and its underlying molecular mechanisms in LC, providing useful information for the development of novel LC treatment strategies.

N6-Methyladenosine Modification on the Function of Female Reproductive Development and Related Diseases

BACKGROUND

N6-methyladenosine (m6A) modification is a widespread and reversible epigenetic alteration in eukaryotic mRNA, playing a pivotal role in various biological functions. Its significance in female reproductive development and associated diseases has recently become a focal point of research.

OBJECTIVE

This review aims to consolidate current knowledge of the role of m6A modification in female reproductive tissues, emphasizing its regulatory dynamics, functional significance, and implications in reproductive health and disease.

METHODS

A comprehensive analysis of recent studies focusing on m6A modification in ovarian development, oocyte maturation, embryo development, and the pathogenesis of reproductive diseases.

RESULTS

m6A modification exhibits dynamic regulation in female reproductive tissues, influencing key developmental stages and processes. It plays critical roles in ovarian development, oocyte maturation, and embryo development, underpinning essential aspects of reproductive health. m6A modification is intricately involved in the pathogenesis of several reproductive diseases, including polycystic ovary syndrome (PCOS), premature ovarian failure (POF), and endometriosis, offering insights into potential molecular mechanisms and therapeutic targets.

CONCLUSION

The review highlights the crucial role of m6A modification in female reproductive development and related diseases. It underscores the need for further research to explore innovative diagnostic and therapeutic strategies for reproductive disorders, leveraging the insights gained from understanding m6A modification's impact on reproductive health.

The m6A-independent role of epitranscriptomic factors in cancer

Protein function alteration and protein mislocalization are cancer hallmarks that drive oncogenesis. N6-methyladenosine (m6A) deposition mediated by METTL3, METTL16, and METTL5 together with the contribution of additional subunits of the m6A system, has shown a dramatic impact on cancer development. However, the cellular localization of m6A proteins inside tumor cells has been little studied so far. Interestingly, recent evidence indicates that m6A methyltransferases are not always confined to the nucleus, suggesting that epitranscriptomic factors may also have multiple oncogenic roles beyond m6A that still represent an unexplored field. To date novel epigenetic drugs targeting m6A modifiers, such as METTL3 inhibitors, are entering into clinical trials, therefore, the study of the potential onco-properties of m6A effectors beyond m6A is required. Here we will provide an overview of methylation-independent functions of the m6A players in cancer, describing the molecular mechanisms involved and the future implications for therapeutics.

The Role of N6-methyladenosine Modification in Gametogenesis and Embryogenesis: Impact on Fertility

The most common epigenetic modification of messenger RNAs (mRNAs) is N6-methyladenosine (m6A), which is mainly located near the 3' untranslated region of mRNAs, near the stop codons, and within internal exons. The biological effect of m6A is dynamically modulated by methyltransferases (writers), demethylases (erasers), and m6A-binding proteins (readers). By controlling post-transcriptional gene expression, m6A has a significant impact on numerous biological functions, including RNA transcription, translation, splicing, transport, and degradation. Hence, m6A influences various physiological and pathological processes, such as spermatogenesis, oogenesis, embryogenesis, placental function, and human reproductive system diseases. During gametogenesis and embryogenesis, genetic material undergoes significant changes, including epigenomic modifications such as m6A. From spermatogenesis and oogenesis to the formation of an oosperm and early embryogenesis, m6A changes occur at every step. m6A abnormalities can lead to gamete abnormalities, developmental delays, impaired fertilization, and maternal-to-zygotic transition blockage. Both mice and humans with abnormal m6A modifications exhibit impaired fertility. In this review, we discuss the dynamic biological effects of m6A and its regulators on gamete and embryonic development and review the possible mechanisms of infertility caused by m6A changes. We also discuss the drugs currently used to manipulate m6A and provide prospects for the prevention and treatment of infertility at the epigenetic level.

Involvement of METTL3-mediated m6A methylation in the early development of porcine cloned embryos

METTL3-mediated N6-methyladenosine (m6A) modification is critical for gametogenesis and early embryonic development. However, the function of METTL3-mediated m6A modification in the early development of somatic nuclear transfer embryos (SCNT) remains unclear. Here, we found that METTL3 mRNA and protein levels exhibit dynamic changes during the early development of porcine SCNT embryos. The levels of METTL3 mRNA and protein in SCNT embryos at specific developmental stages differ from those in parthenogenetic activation (PA) counterparts. SiRNA injection effectively reduced the levels of METTL3 mRNA and protein in 4-cell embryos and blastocysts. METTL3 knockdown significantly reduced the cleavage and blastocyst rates of SCNT embryos. METTL3 knockdown significantly reduced the number of total cells and trophectoderm (TE) cells in the resulting blastocysts and perturbed cell lineage allocation. In addition, METTL3 knockdown reduced the levels of m6A modification in 4-cell embryos and blastocysts. Importantly, METTL3 knockdown decreased the expression levels of CDX2, GATA3, NANOG and YAP, and increased the expression levels of SOX2 and OCT4. Taken together, these results demonstrate that METTL3-mediated m6A modification regulates early development and lineage differentiation of porcine SCNT embryos.

METTL14 mediates nerve growth factor-stimulated testosterone synthesis in porcine theca cells†

Ovarian theca cells produce testosterone, which acts as a vital precursor substance for synthesizing estrogens during follicular development. Nerve growth factor (NGF) has been shown to participate in reproductive physiology, specifically to follicular development and ovulation. There is currently no available data on the impact of NGF on testosterone synthesis in porcine theca cells. Furthermore, m6A modification is the most common internal modification in eukaryotic mRNAs that are closely associated with female gametogenesis, follicle development, ovulation, and other related processes. It is also uncertain whether the three main enzymes associated with m6A, such as Writers, Erasers, and Readers, play a role in this process. The present study, with an in vitro culture model, investigated the effect of NGF on testosterone synthesis in porcine theca cells and the role of Writers-METTL14 in this process. It was found that NGF activates the PI3K/AKT signaling pathway through METTL14, which regulates testosterone synthesis in porcine theca cells. This study will help to further elucidate the mechanisms by which NGF regulates follicular development and provide new therapeutic targets for ovary-related diseases in female animals. Summary Sentence  The present study investigated the effect of NGF on testosterone synthesis in porcine theca cells. It was found that NGF activates the PI3K/AKT signaling pathway through METTL14, which regulates testosterone synthesis in porcine theca cells.

The role of epigenetics in women's reproductive health: the impact of environmental factors

This paper explores the significant role of epigenetics in women's reproductive health, focusing on the impact of environmental factors. It highlights the crucial link between epigenetic modifications-such as DNA methylation and histones post-translational modifications-and reproductive health issues, including infertility and pregnancy complications. The paper reviews the influence of pollutants like PM2.5, heavy metals, and endocrine disruptors on gene expression through epigenetic mechanisms, emphasizing the need for understanding how dietary, lifestyle choices, and exposure to chemicals affect gene expression and reproductive health. Future research directions include deeper investigation into epigenetics in female reproductive health and leveraging gene editing to mitigate epigenetic changes for improving IVF success rates and managing reproductive disorders.

N6-Methyladenosine Modification-Related Genes Express Differentially in Sterile Male Cattle-Yaks

N6-methyladenosine (m6A), an RNA post-transcriptional modification, plays a crucial role in spermatogenesis. Cattle-yaks are interspecific hybrid offsprings of yak and cattle, and male cattle-yaks are sterile. This study aims to investigate the role of m6A modification in male cattle-yak infertility. Herein, testicular tissues were analyzed via histological observations, immunohistochemical assays, reverse-transcription quantitative polymerase chain reaction, Western blotting, and immunofluorescence assays. The results revealed that male cattle-yaks presented smaller testes (5.933 ± 0.4885 cm vs. 7.150 ± 0.3937 cm), with only single cell layers in seminiferous tubules, and weakened signals of m6A regulators such as METTL14 (methyltransferase-like 14), ALKBH5 (alpha-ketoglutarate-dependent hydroxylase homolog 5), FTO (fat mass and obesity-associated protein), and YTHDF2 (YTH N6-methyladenosine RNA binding protein F2), both at the RNA and protein levels, compared with those of yaks. Altogether, these findings suggest that m6A modification may play a crucial role in male cattle-yak sterility, providing a basis for future studies.

METTL3 deficiency leads to ovarian insufficiency due to IL-1β overexpression in theca cells

Premature ovarian insufficiency (POI) is a clinical syndrome characterised by a decline in ovarian function in women before 40 years of age and is associated with oestradiol deficiency and a complex pathogenesis. However, the aetiology of POI is still unclear and effective preventative and treatment strategies are still lacking. Methyltransferase like 3 (METTL3) is an RNA methyltransferase that is involved in spermatogenesis, oocyte development and maturation, early embryonic development, and embryonic stem cell differentiation and formation, but its role in POI is unknown. In the present study, METTL3 deficiency in follicular theca cells was found to lead to reduced fertility in female mice, with a POI-like phenotype, and METTL3 knockout promoted ovarian inflammation. Further, a reduction in METTL3 in follicular theca cells led to a decrease in the m6A modification of pri-miR-21, which further reduced pri-miR-21 recognition and binding by DGCR8 proteins, leading to a decrease in the synthesis of mature miR-21-5p. Decrease of miR-21-5p promoted the secretion of interleukin-1β (IL-1β) from follicular theca cells. Acting in a paracrine manner, IL-1β inhibited the cAMP-PKA pathway and activated the NF-κB pathway in follicular granulosa cells. This activation increased the levels of reactive oxygen species in granulosa cells, causing disturbances in the intracellular Ca2+ balance and mitochondrial damage. These cellular events ultimately led to granulosa cell apoptosis and a decrease in oestradiol synthesis, resulting in POI development. Collectively, these findings reveal how METTL3 deficiency promotes the expression and secretion of IL-1β in theca cells, which regulates ovarian functions, and proposes a new theory for the development of POI disease.

Long-term exposure of metamifop affects sex differentiation and reproductive system of zebrafish (Danio rerio)

The extensive use of herbicide metamifop (MET) in rice fields for weeds control will inevitably lead to its entering into water environments and threaten the aquatic organisms. Previous researches have demonstrated that sublethal exposure of MET significantly affected zebrafish development. Yet the long-term toxicological impacts of MET on aquatic life remains unknown. Herein, we investigated the potential effects of MET (5 and 50 μg/L) on zebrafish during an entire life cycle. Since the expression level of male sex differentiation-related gene dmrt1 and sex hormone synthesis-related gene cyp19a1b were significantly changed after 50 μg/L MET exposure for only 7 days, indicators related to sex differentiation and reproductive system were further investigated. Results showed that the transcript of dmrt1 was inhibited, estradiol content increased and testosterone content decreased in zebrafish of both sexes after MET exposure at 45, 60 and 120 dpf. Histopathological sections showed that the proportions of mature germ cells in the gonads of male and female zebrafish (120 dpf) were significantly decreased. Moreover, males had elevated vitellogenin content while females did not after MET exposure; MET induced feminization in zebrafish, with the proportion of females significantly increased by 19.6% while that of males significantly decreased by 13.2% at 120 dpf. These results suggested that MET interfered with the expression levels of gonad development related-genes, disrupted sex hormone balance, and affected sex differentiation and reproductive system of female and male zebrafish, implying it might have potential endocrine disrupting effects after long-term exposure.

In Search of a Target Gene for a Desirable Phenotype in Aquaculture: Genome Editing of Cyprinidae and Salmonidae Species

Aquaculture supplies the world food market with a significant amount of valuable protein. Highly productive aquaculture fishes can be derived by utilizing genome-editing methods, and the main problem is to choose a target gene to obtain the desirable phenotype. This paper presents a review of the studies of genome editing for genes controlling body development, growth, pigmentation and sex determination in five key aquaculture Salmonidae and Cyprinidae species, such as rainbow trout (Onchorhynchus mykiss), Atlantic salmon (Salmo salar), common carp (Cyprinus carpio), goldfish (Carassius auratus), Gibel carp (Carassius gibelio) and the model fish zebrafish (Danio rerio). Among the genes studied, the most applicable for aquaculture are mstnba, pomc, and acvr2, the knockout of which leads to enhanced muscle growth; runx2b, mutants of which do not form bones in myoseptae; lepr, whose lack of function makes fish fast-growing; fads2, Δ6abc/5Mt, and Δ6bcMt, affecting the composition of fatty acids in fish meat; dnd mettl3, and wnt4a, mutants of which are sterile; and disease-susceptibility genes prmt7, gab3, gcJAM-A, and cxcr3.2. Schemes for obtaining common carp populations consisting of only large females are promising for use in aquaculture. The immobilized and uncolored zebrafish line is of interest for laboratory use.

The reduction of the m6A methyltransferase METTL3 in granulosa cells is related to the follicular cysts in pigs

Follicular cysts are a common reproductive disorder in domestic animals that cause considerable economic losses to the farming industry. Effective prevention and treatment methods are lacking because neither the pathogenesis nor formation mechanisms of follicular cysts are well-understood. In this study, we first investigated the granulosa cells (GCs) of cystic follicles isolated from pigs. We observed a significant reduction in the expression of methyltransferase-like 3 (METTL3). Subsequent experiments revealed that METTL3 downregulation in GCs caused a decrease in m6A modification of pri-miR-21. This reduction further inhibited DGCR8 recognition and binding to pri-miR-21, dampening the synthesis of mature miR-21-5p. Additionally, the decrease in miR-21-5p promotes IL-1β expression in GCs. Elevated IL-1β activates the NFκB pathway, in turn upregulating apoptotic genes TNFa and BAX/BCL2. The subsequent apoptosis of GCs and inhibition of autophagy causes downregulation of CYP19A1 expression. These processes lower oestrogen secretion and contribute to follicular cyst formation. In conclusion, our findings provide a foundation for understanding and further exploring the mechanisms of follicular-cyst development in farm animals. This work has important implications for treating ovarian disorders in livestock and could potentially be extended to humans.

Late gestational exposure to fenvalerate impacts ovarian reserve in neonatal mice via YTHDF2-mediated P-body assembly

Fenvalerate (FEN), a type II pyrethroid pesticide, finds extensive application in agriculture, graziery and public spaces for pest control, resulting in severe environmental pollution. As an environmental endocrine disruptor with estrogen-like activity, exposure to FEN exhibited adverse effects on ovarian functions. Additionally, the presence of the metabolite of FEN in women's urine shows a positive association with the risk of primary ovarian insufficiency (POI). In mammals, the primordial follicle pool established during the early life serves as a reservoir for storing all available oocytes throughout the female reproductive life. The initial size of the primordial follicle pool and the rate of its depletion affect the occurrence of POI. Nevertheless, there is very limited research about the impact of FEN exposure on primordial folliculogenesis. In this study, pregnant mice were orally administrated with 0.2, 2.0 and 20.0 mg/kg FEN from 16.5 to 18.5 days post-coitus (dpc). Ovaries exposed to FEN exhibited the presence of large germ-cell cysts that persist on 1 days post-parturition (1 dpp), followed by a significant reduction in the total number of oocytes in pups on 5 dpp. Moreover, the levels of m6A-RNA and its associated proteins METTL3 and YTHDF2 were significantly increased in the ovaries exposed to FEN. The increased YTHDF2 promoted the assembly of the cytoplasmic processing bodies (P-body) in the oocytes, accompanied with altered expression of transcripts. Additionally, when YTHDF2 was knocked-down in fetal ovary cultures, the primordial folliculogenesis disrupted by FEN exposure was effectively restored. Further, the female offspring exposed to FEN displayed ovarian dysfunctions reminiscent of POI in early adulthood, characterized by decreases in ovarian coefficient and female hormone levels. Therefore, the present study revealed that exposure to FEN during late pregnancy disrupted primordial folliculogenesis by YTHDF2-mediated P-body assembly, causing enduring adverse effects on female fertility.

GnRH-driven FTO-mediated RNA m6A modification promotes gonadotropin synthesis and secretion

BACKGROUND

Gonadotropin precisely controls mammalian reproductive activities. Systematic analysis of the mechanisms by which epigenetic modifications regulate the synthesis and secretion of gonadotropin can be useful for more precise regulation of the animal reproductive process. Previous studies have identified many differential m6A modifications in the GnRH-treated adenohypophysis. However, the molecular mechanism by which m6A modification regulates gonadotropin synthesis and secretion remains unclear.

RESULTS

Herein, it was found that GnRH can promote gonadotropin synthesis and secretion by promoting the expression of FTO. Highly expressed FTO binds to Foxp2 mRNA in the nucleus, exerting a demethylation function and reducing m6A modification. After Foxp2 mRNA exits the nucleus, the lack of m6A modification prevents YTHDF3 from binding to it, resulting in increased stability and upregulation of Foxp2 mRNA expression, which activates the cAMP/PKA signaling pathway to promote gonadotropin synthesis and secretion.

CONCLUSIONS

Overall, the study reveals the molecular mechanism of GnRH regulating the gonadotropin synthesis and secretion through FTO-mediated m6A modification. The results of this study allow systematic interpretation of the regulatory mechanism of gonadotropin synthesis and secretion in the pituitary at the epigenetic level and provide a theoretical basis for the application of reproductive hormones in the regulation of animal artificial reproduction.

Regulatory role of m6A epitranscriptomic modifications in normal development and congenital malformations during embryogenesis

The discovery of N6-methyladenosine (m6A) methylation and its role in translation has led to the emergence of a new field of research. Despite accumulating evidence suggesting that m6A methylation is essential for the pathogenesis of cancers and aging diseases by influencing RNA stability, localization, transformation, and translation efficiency, its role in normal and abnormal embryonic development remains unclear. An increasing number of studies are addressing the development of the nervous and gonadal systems during embryonic development, but only few are assessing that of the immune, hematopoietic, urinary, and respiratory systems. Additionally, these studies are limited by the requirement for reliable embryonic animal models and the difficulty in collecting tissue samples of fetuses during development. Multiple studies on the function of m6A methylation have used suitable cell lines to mimic the complex biological processes of fetal development or the early postnatal phase; hence, the research is still in the primary stage. Herein, we discuss current advances in the extensive biological functions of m6A methylation in the development and maldevelopment of embryos/fetuses and conclude that m6A modification occurs extensively during fetal development. Aberrant expression of m6A regulators is probably correlated with single or multiple defects in organogenesis during the intrauterine life. This comprehensive review will enhance our understanding of the pivotal role of m6A modifications involved in fetal development and examine future research directions in embryogenesis.

Methyltransferase-like 3 mediated RNA m6 A modifications in the reproductive system: Potentials for diagnosis and therapy

Several studies have highlighted the functional indispensability of methyltransferase-like 3 (METTL3) in the reproductive system. However, a review that comprehensively interprets these studies and elucidates their relationships is lacking. Therefore, the present work aimed to review studies that have investigated the functions of METTL3 in the reproductive system (including spermatogenesis, follicle development, gametogenesis, reproductive cancer, asthenozoospermia and assisted reproduction failure). This review suggests that METTL3 functions not only essential for normal development, but also detrimental in the occurrence of disorders. In addition, promising applications of METTL3 as a diagnostic or prognostic biomarker and therapeutic target for reproductive disorders have been proposed. Collectively, this review provides comprehensive interpretations, novel insights, potential applications and future perspectives on the role of METTL3 in regulating the reproductive system, which may be a valuable reference for researchers and clinicians.

High Temperature-Induced m6A Epigenetic Changes Affect Early Porcine Embryonic Developmental Competence in Pigs

N6-methyladenosine (m6A), the most prevalent modification in eukaryotic messenger RNA (mRNA), plays a key role in various developmental processes in mammals. Three proteins that affect RNA m6A modification have been identified: methyltransferases, demethylases, and m6A-binding proteins, known as "writer," "eraser," and "reader" proteins, respectively. However, changes in the m6A modification when early porcine embryos are exposed to stress remain unclear. In this study, we exposed porcine oocytes to a high temperature (HT, 41°C) for 10 h, after which the mature oocytes were parthenogenetically activated and cultured for 7 days to the blastocyst stage. HT significantly decreased the rates of the first polar body extrusion and blastocyst formation. Further detection of m6A modification found that HT can lead to increased expression levels of "reader," YTHDF2, and "writer," METTL3, and decreased expression levels of "eraser," FTO, resulting in an increased level of m6A modification in the embryos. Additionally, heat shock protein 70 (HSP70) is upregulated under HT conditions. Our study demonstrated that HT exposure alters m6A modification levels, which further affects early porcine embryonic development.

FTO-mediated m6A demethylation regulates GnRH expression in the hypothalamus via the PLCβ3/Ca2+/CAMK signalling pathway

N6-methyladenosine (m6A) plays a crucial role in the development and functional homeostasis of the central nervous system. The fat mass and obesity-associated (FTO) gene, which is highly expressed in the hypothalamus, is closely related to female pubertal development. In this study, we found that m6A methylation decreased in the hypothalamus gradually with puberty and decreased in female rats with precocious puberty. FTO expression was increased at the same time. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) showed that the m6A methylation of PLCβ3, a key enzyme of the Ca2+ signalling pathway, was decreased significantly in the hypothalamus in precocious rats. Upregulating FTO increased PLCβ3 expression and activated the Ca2+ signalling pathway, which promoted GnRH expression. Dual-luciferase reporter and MeRIP-qPCR assays confirmed that FTO regulated m6A demethylation of PLCβ3 and promoted PLCβ3 expression. Upon overexpressing FTO in the hypothalamic arcuate nucleus (ARC) in female rats, we observed advanced puberty onset. Meanwhile, PLCβ3 and GnRH expression in the hypothalamus increased significantly, and the Ca2+ signalling pathway was activated. Our study demonstrates that FTO enhances GnRH expression, which promotes puberty onset, by regulating m6A demethylation of PLCβ3 and activating the Ca2+ signalling pathway.

The Role of BDNF, YBX1, CENPF, ZSCAN4, TEAD4, GLIS1 and USF1 in the Activation of the Embryonic Genome in Bovine Embryos

Early embryonic development relies on the maternal RNAs and newly synthesized proteins during oogenesis. Zygotic transcription is an important event occurring at a specific time after fertilization. If no zygotic transcription occurs, the embryo will die because it is unable to meet the needs of the embryo and continue to grow. During the early stages of embryonic development, the correct transcription, translation, and expression of genes play a crucial role in blastocyst formation and differentiation of cell lineage species formation among mammalian species, and any variation may lead to developmental defects, arrest, or even death. Abnormal expression of some genes may lead to failure of the embryonic zygote genome before activation, such as BDNF and YBX1; Decreased expression of CENPF, ZSCAN4, TEAD4, GLIS1, and USF1 genes can lead to embryonic development failure. This article reviews the results of studies on the timing and mechanism of gene expression of these genes in bovine fertilized eggs/embryos.

N6-methyladenosine methyltransferase METTL3 modulates the cell cycle of granulosa cells via CCND1 and AURKB in Haimen goats

N6-methyladenosine (m6A) plays a crucial role in many bioprocesses across species, but its function in granulosa cells during oocyte maturation is not well understood in animals, especially domestic animals. We observed an increase in m6A methyltransferase-like 3 (METTL3) in granulosa cells during oocyte maturation in Haimen goats. Our results showed that knockdown of METTL3 disrupted the cell cycle in goat granulosa cells, leading to aggravated cell apoptosis and inhibition of cell proliferation and hormone secretion. Mechanistically, METTL3 may regulate the cell cycle in goat granulosa cells by mediating Aurora kinase B (AURKB) mRNA degradation in an m6A-YTH N6-methyladenosine RNA binding protein 2 (YTHDF2) manner and participating in AURKB transcription via the Cyclin D1 (CCND1)-Retinoblastoma protein (RB)-E2F transcription factor 1 (E2F1) pathway. Overall, our study highlights the essential role of METTL3 in granulosa cells during oocyte maturation in Haimen goats. These findings provide a theoretical basis and technical means for understanding how RNA methylation participates in oocyte maturation through granulosa cells.

m6A Regulator-mediated RNA Methylation Modulates Immune Microenvironment of Hepatitis B Virus-related Acute Liver Failure

Acute liver failure (ALF) is a rare and complicated disease with a high mortality rate. Emergency liver transplantation is the only treatment method that can improve the ALF prognosis. However, its clinical application remains limited owing to the aggressive nature of liver transplantation, limited donors, and high postoperative mortality. The study investigated the effect of m6A on the immune microenvironment of hepatitis B virus-related ALF (HBV-ALF). In this study, the gene expression data of 47 normal people and 42 HBV-ALF patients were downloaded from the Gene Expression Omnibu (GEO) database. The known 23 m6A regulators which mediated RNA modification patterns were compared and analyzed in these two groups, and the gene diagnosis model of HBV-ALF patients was established based on the analysis results. In addition, we used unsupervised clustering to identify different m6A RNA methylation modification patterns in HBV-ALF based on m6A regulators, and evaluated the immune infiltration and biological differences in these subtypes. In addition, the relationship between m6A genes and immune cell activation in HBV-ACLF patients was explored by immune infiltration analysis. Nineteen m6A regulators mediated RNA methylation (m6A regulators for short) were differentially expressed in HBV-ALF and control groups. m6A regulators could well distinguish control samples from HBV-ALF samples, and m6A regulators might be used as a basis for diagnosing HBV-ALF patients. Immune cells such as activated CD8 T cells, activated B cells, and activated CD4 T cells might play important roles in HBV-ALF, and m6A regulators were closely associated with immune cell infiltration. ALKBH15, CBLL1, IGF2BP2, IGF2BP3, and ZC3H13 were significantly associated with immune cells. Considering 23 m6A regulators, HBV-ALF patients could be classified into two subtypes (cluster 1 and cluster 2) based on different immune cell infiltration. m6A regulators of the IGFBP and YHDF families have extremely different levels in these two subtypes. Differential immune cell infiltration among these subtypes was observed, a total of 913 differentially expressed genes among different m6A modification patterns was identified, and their biological functions were explored. m6A modification might play a crucial role in the diverse and complex immune microenvironment of HBV-ALF patients.

Transcriptome Studies Reveal the N6-Methyladenosine Differences in Testis of Yaks at Juvenile and Sexual Maturity Stages

Studying the mechanism of spermatogenesis is key to exploring the reproductive characteristics of male yaks. Although N6-methyladenosine (m6A) RNA modification has been reported to regulate spermatogenesis and reproductive function in mammals, the molecular mechanism of m6A in yak testis development and spermatogenesis remains largely unknown. Therefore, we collected testicular tissue from juvenile and adult yaks and found that the m6A level significantly increased after sexual maturity in yaks. In MeRIP-seq, 1702 hypermethylated peaks and 724 hypomethylated peaks were identified. The hypermethylated differentially methylated RNAs (DMRs) (CIB2, AK1, FOXJ2, PKDREJ, SLC9A3, and TOPAZ1) mainly regulated spermatogenesis. Functional enrichment analysis showed that DMRs were significantly enriched in the adherens junction, gap junction, and Wnt, PI3K, and mTOR signaling pathways, regulating cell development, spermatogenesis, and testicular endocrine function. The functional analysis of differentially expressed genes showed that they were involved in the biological processes of mitosis, meiosis, and flagellated sperm motility during the sexual maturity of yak testis. We also screened the key regulatory factors of testis development and spermatogenesis by combined analysis, which included BRCA1, CREBBP, STAT3, and SMAD4. This study indexed the m6A characteristics of yak testicles at different developmental stages, providing basic data for further research of m6A modification regulating yak testicular development.

RNA epigenetic modifications in ovarian cancer: The changes, chances, and challenges

Ovarian cancer (OC) is the most common female cancer worldwide. Patients with OC have high mortality because of its complex and poorly understood pathogenesis. RNA epigenetic modifications, such as m6 A, m1 A, and m5 C, are closely associated with the occurrence and development of OC. RNA modifications can affect the stability of mRNA transcripts, nuclear export of RNAs, translation efficiency, and decoding accuracy. However, there are few overviews that summarize the link between m6 A RNA modification and OC. Here, we discuss the molecular and cellular functions of different RNA modifications and how their regulation contributes to the pathogenesis of OC. By improving our understanding of the role of RNA modifications in the etiology of OC, we provide new perspectives for their use in OC diagnosis and treatment. This article is categorized under: RNA Processing > RNA Editing and Modification RNA in Disease and Development > RNA in Disease.

A cleaved METTL3 potentiates the METTL3-WTAP interaction and breast cancer progression

N6-methyladenosine (m6A) methylation of RNA by the methyltransferase complex (MTC), with core components including METTL3-METTL14 heterodimers and Wilms' tumor 1-associated protein (WTAP), contributes to breast tumorigenesis, but the underlying regulatory mechanisms remain elusive. Here, we identify a novel cleaved form METTL3a (residues 239-580 of METTL3). We find that METTL3a is required for the METTL3-WTAP interaction, RNA m6A deposition, as well as cancer cell proliferation. Mechanistically, we find that METTL3a is essential for the METTL3-METTL3 interaction, which is a prerequisite step for recruitment of WTAP in MTC. Analysis of m6A sequencing data shows that depletion of METTL3a globally disrupts m6A deposition, and METTL3a mediates mammalian target of rapamycin (mTOR) activation via m6A-mediated suppression of TMEM127 expression. Moreover, we find that METTL3 cleavage is mediated by proteasome in an mTOR-dependent manner, revealing positive regulatory feedback between METTL3a and mTOR signaling. Our findings reveal METTL3a as an important component of MTC, and suggest the METTL3a-mTOR axis as a potential therapeutic target for breast cancer.

N6-adenosine (m6A) mRNA methylation is required for Tribolium castaneum development and reproduction

Gene expression is regulated at various levels, including post-transcriptional mRNA modifications, where m6A methylation is the most common modification of mRNA. The m6A methylation regulates multiple stages of mRNA processing, including splicing, export, decay, and translation. How m6A modification is involved in insect development is not well known. We used the red flour beetle, Tribolium castaneum, as a model insect to identify the role of m6A modification in insect development. RNA interference (RNAi)-mediated knockdown of genes coding for m6A writers (m6A methyltransferase complex, depositing m6A to mRNA) and readers (YTH-domain proteins, recognizing and executing the function of m6A) was conducted. Knockdown of most writers during the larval stage caused a failure of ecdysis during eclosion. The loss of m6A machinery sterilized both females and males by interfering with the functioning of reproductive systems. Females treated with dsMettl3, the main m6A methyltransferase, laid significantly fewer and reduced-size eggs than the control insects. In addition, the embryonic development in eggs laid by dsMettl3 injected females was terminated in the early stages. Knockdown studies also showed that the cytosol m6A reader, YTHDF, is likely responsible for executing the function of m6A modifications during insect development. These data suggest that m6A modifications are critical for T. castaneum development and reproduction.

Premature ovarian insufficiency: a review on the role of oxidative stress and the application of antioxidants

Normal levels of reactive oxygen species (ROS) play an important role in regulating follicular growth, angiogenesis and sex hormone synthesis in ovarian tissue. When the balance between ROS and antioxidants is disrupted, however, it can cause serious consequences of oxidative stress (OS), and the quantity and quality of oocytes will decline. Therefore, this review discusses the interrelationship between OS and premature ovarian insufficiency (POI), the potential mechanisms and the methods by which antioxidants can improve POI through controlling the level of OS. We found that OS can mediate changes in genetic materials, signal pathways, transcription factors and ovarian microenvironment, resulting in abnormal apoptosis of ovarian granulosa cells (GCs) and abnormal meiosis as well as decreased mitochondrial Deoxyribonucleic Acid(mtDNA) and other changes, thus accelerating the process of ovarian aging. However, antioxidants, mesenchymal stem cells (MSCs), biological enzymes and other antioxidants can delay the disease process of POI by reducing the ROS level in vivo.

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.

A Cryptic Sex-Linked Locus Revealed by the Elimination of a Master Sex-Determining Locus in Medaka Fish

AbstractSex chromosomes rapidly turn over in several taxonomic groups. Sex chromosome turnover is generally thought to start with the appearance of a new sex-determining gene on an autosome while an old sex-determining gene still exists, followed by the fixation of the new one. However, we do not know how prevalent the transient state is, where multiple sex-determining loci coexist within natural populations. Here, we removed a Y chromosome with a master male-determining gene DMY from medaka fish using high temperature-induced sex-reversed males. After four generations, the genomic characteristics of a sex chromosome were found on one chromosome, which was an autosome in the original population. Thus, the elimination of a master sex-determining locus can reveal a cryptic locus with a possible sex-determining effect, which can be the seed for sex chromosome turnover. Our results suggest that populations that seem to have a single-locus XY system may have other chromosomal regions with sex-determining effects. In conclusion, the coexistence of multiple sex-determining genes in a natural population may be more prevalent than previously thought. Experimental elimination of a master sex-determining locus may serve as a promising method for finding a locus that can be a protosex chromosome.

Effect of prenatal perfluoroheptanoic acid exposure on spermatogenesis in offspring mice

BACKGROUND

Perfluoroheptanoic acid (PFHpA), a persistent organic pollutant widespread in the environment, is suspected as an environmental endocrine disruptor for its disturbance effect on hormone homeostasis and reproductive development. Whereas the effect of intrauterine PFHpA exposure during gestation on spermatogenesis of male offspring mice is still unknown.

OBJECTIVE

This study aimed to explore the effect of prenatal PFHpA exposure on the reproductive development of male offspring mice and the role of N6-methyladenosine (m6A) during the process.

METHODS

Fifty-six C57BL/6 pregnant mice were randomly divided into 4 groups. During the gestation period, the pregnant mice were exposed to 0, 0.0015, 0.015, and 0.15 mg/kg bw/d PFHpA from gestational day 1 (GD1) to GD16 by oral gavage. The male offspring mice were sacrificed by spinal dislocation at 7 weeks old. The body weight, testicular weight, and brain weight were weighed, and the intra-testicular testosterone was detected. The sperm qualities were analyzed with computer-aided sperm analysis (CASA). The testicular tissues were taken to analyze the pathological changes and examine the global m6A RNA methylation levels. Quantitative real-time PCR (qRT-PCR) was adopted to figure out the mRNA expression levels of m6A-related enzymes in testicular tissues of different PFHpA treated groups. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) was applied to further explore the m6A RNA methylation at a whole-genome scale.

RESULTS

Compared with the control group, no significant differences were observed in body weight, testicular weight, testicular coefficient, and the visceral-brain ratio of testicular tissue in the PFHpA treated groups. And no significant change was observed in intra-testicular testosterone among the four groups. CASA results showed a decrease of sperm count, sperm concentration, and total cell count, as well as an increase of sperm progressive cells' head area after prenatal PFHpA exposure (P < 0.05). Hematoxylin and eosin staining of pathological sections showed seminiferous tubules morphological change, disorder arrangement of seminiferous epithelium, and reduction of spermatogenic cells in the PFHpA treated groups. PFHpA significantly decreased global levels of m6A RNA methylation in testicular tissue (P < 0.05). Besides, qRT-PCR results showed significant alteration of the mRNA expression levels of seven m6A-related enzymes (Mettl3, Mettl5, Mettl14, Pcif1, Wtap, Hnrnpa2b1, and Hnrnpc) in the PFHpA treated groups (P < 0.05). MeRIP-seq results showed a correlation between prenatal PFHpA exposure and activation and binding of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Cnga3 and Mpzl3 showed differential expression in the enrichment subcategories or pathways.

CONCLUSIONS

Exposure to PFHpA during the gestation period would adversely affect the development of seminiferous tubules and testicular m6A RNA methylation in offspring mice, which subsequently interferes with spermatogenesis and leads to reproductive toxicity.

Sex blind: bridging the gap between drug exposure and sex-related gene expression in Danio rerio using next-generation sequencing (NGS) data and a literature review to find the missing links in pharmaceutical and environmental toxicology studies

The sex of both humans and Danio rerio has previously been shown to affect the way individuals respond to drug exposure. Genes which allow identification of sex in juvenile zebrafish show potential to reveal these confounding variables between sex in toxicological and preclinical trials but the link between these is so far missing. These sex-specific, early expressed genes where expression is not altered by drug exposure must be carefully selected for this purpose. We aimed to discover genes which can be used in pharmaceutical trials and environmental toxicology studies to uncover sex-related variations in gene expression with drug application using the model organism Danio rerio. Previously published early sex determining genes from King et al. were evaluated as well as additional genes selected from our zebrafish Next-generation sequencing (NGS) data which are known from previously published works not to be susceptible to changes in expression with drug exposure. NGS revealed a further ten female-specific genes (vtg1, cyp17a1, cyp19a1a, igf3, ftz-f1, gdf9, foxl2a, Nr0b1, ipo4, lhcgr) and five male related candidate genes (FKBP5, apobb1, hbaa1, dmrt1, spata6) which are also expressed in juvenile zebrafish, 28 days post fertilisation (dpf). Following this, a literature review was performed to classify which of these early-expressed sex specific genes are already known to be affected by drug exposure in order to determine candidate genes to be used in pharmaceutical trials or environmental toxicology testing studies. Discovery of these early sex-determining genes in Danio rerio will allow identification of sex-related responses to drug testing to improve sex-specific healthcare and the medical treatment of human patients.

RNA methyltransferases in plants: Breakthroughs in function and evolution

Each day it is becoming increasingly difficult not to notice the completely new, fast growing, extremely intricate and challenging world of epitranscriptomics as the understanding of RNA methylation is expanding at a hasty rate. Writers (methyltransferases), erasers (demethylases) and readers (RNA-binding proteins) are responsible for adding, removing and recognising methyl groups on RNA, respectively. Several methyltransferases identified in plants are now being investigated and recent studies have shown a connection between RNA-methyltransferases (RNA-MTases) and stress and development processes. However, compared to their animal and bacteria counterparts, the understanding of RNA methyltransferases is still incipient, particularly those located in organelles. Comparative and systematic analyses allowed the tracing of the evolution of these enzymes suggesting the existence of several methyltransferases yet to be characterised. This review outlines the functions of plant nuclear and organellar RNA-MTases in plant development and stress responses and the comparative and evolutionary discoveries made on RNA-MTases across kingdoms.

The role of post-transcriptional modifications during development

While the existence of post-transcriptional modifications of RNA nucleotides has been known for decades, in most RNA species the exact positions of these modifications and their physiological function have been elusive until recently. Technological advances, such as high-throughput next-generation sequencing (NGS) methods and nanopore-based mapping technologies, have made it possible to map the position of these modifications with single nucleotide accuracy, and genetic screens have uncovered the “writer”, “reader” and “eraser” proteins that help to install, interpret and remove such modifications, respectively. These discoveries led to intensive research programmes with the aim of uncovering the roles of these modifications during diverse biological processes. In this review, we assess novel discoveries related to the role of post-transcriptional modifications during animal development, highlighting how these discoveries can affect multiple aspects of development from fertilization to differentiation in many species.

Characterization of N6-methyladenosine in cattle-yak testis tissue

N⁶-methyladenosine (m⁶A) is the most common form of eukaryotic mRNA modification, and it has been shown to exhibit broad regulatory activity in yeast, plants, and mammals. The specific role of m⁶A methylation as a regulator of spermatogenesis, however, has yet to be established. In this experiment, through a series of preliminary studies and methylated RNA immunoprecipitation sequencing, the m⁶A map of cattle-yak testicular tissue was established as a means of exploring how m⁶A modification affects cattle-yak male infertility. Cattle-yak testis tissues used in this study were found to contain sertoli cells and spermatogonia. Relative to sexually mature yak samples, those isolated from cattle-yak testis exhibited slightly reduced levels of overall methylation, although these levels were significantly higher than those in samples from pre-sexually mature yaks. Annotation analyses revealed that differentially methylated peaks were most concentrated in exonic regions, with progressively lower levels of concentration in the 3'-untranslated region (UTR) and 5'-UTR regions. To further explore the role of such m⁶A modification, enrichment analyses were performed on differentially methylated and differentially expressed genes in these samples. For the cattle-yaks vs. 18-months-old yaks group comparisons, differentially methylated genes were found to be associated with spermatogenesis-related GO terms related to the cytoskeleton and actin-binding, as well as with KEGG terms related to the regulation of the actin cytoskeleton and the MAPK signaling pathway. Similarly, enrichment analyses performed for the cattle-yaks vs. 5-years-old yaks comparison revealed differentially methylated genes to be associated with GO terms related to protein ubiquitination, ubiquitin ligase complexes, ubiquitin-dependent protein catabolism, and endocytotic activity, as well as with KEGG terms related to apoptosis and the Fanconi anemia pathway. Overall, enrichment analyses for the cattle-yaks vs. 18-months-old yaks comparison were primarily associated with spermatogenesis, whereas those for the cattle-yaks vs. 5-years-old yaks comparison were primarily associated with apoptosis.

The Role of m6A on Female Reproduction and Fertility: From Gonad Development to Ovarian Aging

The growth and maturation of oocyte is accompanied by the accumulation of abundant RNAs and posttranscriptional regulation. N6-methyladenosine (m⁶A) is the most prevalent epigenetic modification in mRNA, and precisely regulates the RNA metabolism as well as gene expression in diverse physiological processes. Recent studies showed that m⁶A modification and regulators were essential for the process of ovarian development and its aberrant manifestation could result in ovarian aging. Moreover, the specific deficiency of m⁶A regulators caused oocyte maturation disorder and female infertility with defective meiotic initiation, subsequently the oocyte failed to undergo germinal vesicle breakdown and consequently lost the ability to resume meiosis by disrupting spindle organization as well as chromosome alignment. Accumulating evidence showed that dysregulated m⁶A modification contributed to ovarian diseases including polycystic ovarian syndrome (PCOS), primary ovarian insufficiency (POI), ovarian aging and other ovarian function disorders. However, the complex and subtle mechanism of m⁶A modification involved in female reproduction and fertility is still unknown. In this review, we have summarized the current findings of the RNA m⁶A modification and its regulators in ovarian life cycle and female ovarian diseases. And we also discussed the role and potential clinical application of the RNA m⁶A modification in promoting oocyte maturation and delaying the reproduction aging.

The molecular characteristics in different procedures of spermatogenesis

Spermatogenesis is a multistep biological process. In addition to somatic cells, it involves the orderly differentiation of dozens of spermatogenic cells. In this process, the regulatory networks between different spermatogenic cell populations are significantly different. RNA m6A regulators and miRNAs have been found to be closely related to spermatogenesis in recent years, and they are an important part of the above regulatory networks. Understanding gene expression and its rules in different spermatogenic cell populations will help in the in-depth exploration of their detailed roles in spermatogenesis. This study collected a public dataset of nonobstructive azoospermia (NOA). Based on the Johnson score, the testicular samples of NOA were divided into three types, Sertoli-cell only syndrome, meiotic arrest and postmeiotic arrest, which represented the loss of three germ cell populations, including whole spermatogenic cells, postmeiotic spermatogenic cells, and a mixture of late spermatids and spermatozoa, respectively. The aforementioned three types of testis data were compared with normal testis data, and the molecular expression characteristics of the abovementioned three germ cell populations were obtained. Our study showed that different germ cell populations have different active molecules and their pathways. In addition, RNA m6A regulators, including METTL3, IGF2BP2 and PRRC2A, and miRNAs, including hsa-let-7a-2, hsa-let-7f-1, hsa-let-7g, hsa-miR-15a, hsa-miR-197, hsa-miR-21, hsa-miR-30e, hsa-miR-32, hsa-miR-503 and hsa-miR-99a, also presented regulatory roles in almost all germ cells.

The transcriptome-wide N6-methyladenosine (m6A) map profiling reveals the regulatory role of m6A in the yak ovary

BACKGROUND AND AIM

Yak estrus is a seasonal phenomenon, probably involving epigenetic regulation of synthesis and secretion of sex hormones as well as growth and development of follicles. N6-methyladenosine (m⁶A) is the most common internal modification of the eukaryotic mRNA. However, there are no detailed reports on the m⁶A transcriptome map of yak ovary. Therefore, this study aimed to collected the yak ovarian tissues at three different states of anestrus (YO-A), estrus (YO-F), and pregnancy (YO-P), and obtained the full transcriptome m⁶A map in yak by MeRIP-seq.

RESULTS

The HE staining revealed that the number of growing follicles and mature follicles in the ovary during the estrus period was relatively higher than those in the anestrus period and the pregnancy period. The RT-qPCR showed that the expression of METTL3, METTL14, FTO, YTHDC1 were significantly different across different periods in the ovaries, which suggests that m⁶A may play a regulatory role in ovarian activity. Next, we identified 20,174, 19,747 and 13,523 m⁶A peaks in the three ovarian samples of YO-A, YO-F and YO-P using the methylated RNA immunoprecipitation sequencing (MeRIP-seq). The m⁶A peaks are highly enriched in the coding sequence (CDS) region and 3'untranslated region (3'UTR) as well as the conserved sequence of "RRACH." The GO, KEGG and GSEA analysis revealed the involvement of m⁶A in many physiological activities of the yak's ovary during reproductive cycle. The association analysis found that some genes such as BNC1, HOMER1, BMP15, BMP6, GPX3, and WNT11 were related to ovarian functions.

CONCLUSIONS

The comparison of the distribution patterns of methylation peaks in the ovarian tissues across different periods further explored the m⁶A markers related to the regulation of ovarian ovulation and follicular development in the yak ovary. This comprehensive map provides a solid foundation for revealing the potential function of the mRNA m⁶A modification in the yak ovary.

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.

On the genetic architecture of rapidly adapting and convergent life history traits in guppies

The genetic basis of traits shapes and constrains how adaptation proceeds in nature; rapid adaptation can proceed using stores of polygenic standing genetic variation or hard selective sweeps, and increasing polygenicity fuels genetic redundancy, reducing gene re-use (genetic convergence). Guppy life history traits evolve rapidly and convergently among natural high- and low-predation environments in northern Trinidad. This system has been studied extensively at the phenotypic level, but little is known about the underlying genetic architecture. Here, we use four independent F2 QTL crosses to examine the genetic basis of seven (five female, two male) guppy life history phenotypes and discuss how these genetic architectures may facilitate or constrain rapid adaptation and convergence. We use RAD-sequencing data (16,539 SNPs) from 370 male and 267 female F2 individuals. We perform linkage mapping, estimates of genome-wide and per-chromosome heritability (multi-locus associations), and QTL mapping (single-locus associations). Our results are consistent with architectures of many loci of small-effect for male age and size at maturity and female interbrood period. Male trait associations are clustered on specific chromosomes, but female interbrood period exhibits a weak genome-wide signal suggesting a potentially highly polygenic component. Offspring weight and female size at maturity are also associated with a single significant QTL each. These results suggest rapid, repeatable phenotypic evolution of guppies may be facilitated by polygenic trait architectures, but subsequent genetic redundancy may limit gene re-use across populations, in agreement with an absence of strong signatures of genetic convergence from recent analyses of wild guppies.

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.

YBX1 mediates alternative splicing and maternal mRNA decay during pre-implantation development

Background

In mammals, maternal gene products decay and zygotic genome activation (ZGA) during maternal to zygotic transition (MZT) is critical for the early embryogenesis. Y-box binding protein YBX1 plays vital roles in RNA stabilization and transcriptional regulation, but its roles remain to be elucidated during pre-implantation development.

Methods

In the present study, we re-analyzed transcriptional level of YBX1 in mice, human, bovine, and goat embryos using public RNA-seq datasets. We further performed siRNA microinjection to knock down the expression of YBX1, and RNA sequencing of the 8-cell stage embryos in the control and YBX1 knockdown group. To reveal the regulation mechanisms of YBX1, we conducted differentially expression analysis, alternative splicing (AS) analysis, enrichment analysis, and 5-EU staining using DESeq2, rMATs, clusterProfiler, and immunofluorescence technique, respectively.

Results

The expression of YBX1 was increased during MZT in goat, bovine, human, and mice, but significantly decreased in YBX1 knockdown embryos compared with the controls, suggesting successfully knockdown of YBX1. The percentage of blastocyst was decreased, while embryos blocked at the 2- and 4-cell stage were increased in YBX1 knockdown embryos compared to the controls. Using RNA-seq, we identified 1623 up-regulated and 3531 down-regulated genes in the 8-cell stage YBX1 knockdown embryos. Of note, the down-regulated genes were enriched in regulation of RNA/mRNA stability and spliceosome, suggesting that YBX1 might medicate RNA stability and AS. To this end, we identified 3284 differential AS events and 1322 differentially expressed maternal mRNAs at the 8-cell stage YBX1 knockdown embryos. Meanwhile, the splicing factors and mRNA decay-related genes showed aberrant expression, and the transcriptional activity during ZGA in goat and mice was compromised when YBX1 was knocked down.

Conclusion

YBX1 serves an important role in maternal mRNA decay, alternative splicing, and the transcriptional activity required for early embryogenesis, which will broaden the current understanding of YBX1 functions during the stochastic reprogramming events.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00743-4.

Nanoparticle-Induced m6A RNA Modification: Detection Methods, Mechanisms and Applications

With the increasing application of nanoparticles (NPs) in medical and consumer applications, it is necessary to ensure their safety. As m⁶A (N⁶-methyladenosine) RNA modification is one of the most prevalent RNA modifications involved in many diseases and essential biological processes, the relationship between nanoparticles and m⁶A RNA modification for the modulation of these events has attracted substantial research interest. However, there is limited knowledge regarding the relationship between nanoparticles and m⁶A RNA modification, but evidence is beginning to emerge. Therefore, a summary of these aspects from current research on nanoparticle-induced m⁶A RNA modification is timely and significant. In this review, we highlight the roles of m⁶A RNA modification in the bioimpacts of nanoparticles and thus elaborate on the mechanisms of nanoparticle-induced m⁶A RNA modification. We also summarize the dynamic regulation and biofunctions of m⁶A RNA modification. Moreover, we emphasize recent advances in the application perspective of nanoparticle-induced m⁶A RNA modification in medication and toxicity of nanoparticles to provide a potential method to facilitate the design of nanoparticles by deliberately tuning m⁶A RNA modification.

N6-Methyladenosine Modifications in the Female Reproductive System: Roles in Gonad Development and Diseases

N6-methyladenosine (m⁶A) is the most prevalent chemical modification in eukaryotic messenger RNAs. By participating in various RNA-related bioprocesses including RNA decay, splicing, transport and translation, m⁶A serves as a pivotal regulator of RNA fate and plays an irreplaceable role in cellular activities. The m⁶A modifications of transcripts are coordinately regulated by methyltransferase “writers” and demethylase “erasers”, and produce variable effects via different m⁶A reading protein “readers”. There is emerging evidence that m⁶A modifications play a critical role in a variety of physiological and pathological processes in the female reproductive system, subsequently affecting female fertility. Here, we introduce recent advances in research on m⁶A regulators and their functions, then highlight the role of m⁶A in gonad development and female reproductive diseases, as well as the underlying mechanisms driving these processes.

RNA m6A Modification in Immunocytes and DNA Repair: The Biological Functions and Prospects in Clinical Application

As the most prevalent internal modification in mRNA, N⁶-methyladenosine (m⁶A) plays broad biological functions via fine-tuning gene expression at the post-transcription level. Such modifications are deposited by methyltransferases (i.e., m⁶A Writers), removed by demethylases (i.e., m⁶A Erasers), and recognized by m⁶A binding proteins (i.e., m⁶A Readers). The m⁶A decorations regulate the stability, splicing, translocation, and translation efficiency of mRNAs, and exert crucial effects on proliferation, differentiation, and immunologic functions of immunocytes, such as T lymphocyte, B lymphocyte, dendritic cell (DC), and macrophage. Recent studies have revealed the association of dysregulated m⁶A modification machinery with various types of diseases, including AIDS, cancer, autoimmune disease, and atherosclerosis. Given the crucial roles of m⁶A modification in activating immunocytes and promoting DNA repair in cells under physiological or pathological states, targeting dysregulated m⁶A machinery holds therapeutic potential in clinical application. Here, we summarize the biological functions of m⁶A machinery in immunocytes and the potential clinical applications via targeting m⁶A machinery.

The function of the m6A methyltransferase METTL3 in goat early embryo development under hypoxic and normoxic conditions

It has been reported that N6-methyladenosine (m6A) methyltransferase-like 3 (METTL3) plays an important role in zygote genome activation during embryonic development, but the effects of METTL3 under oxidative stress in the early development of goat embryos remain largely unknown. In this study, zygotes were monitored at 72 and 168 h after fertilization, and they developed to the 8-cell stage and blastocyst stage under hypoxic conditions and normoxic conditions. Single-cell transcriptome sequencing was performed at the 8-cell stage and the blastocyst stage in the goat embryos, the differentially expressed METTL3 was screened from the sequencing results. We found that microinjection of small interfering RNA (siRNA) against METTL3 caused developmental arrest, both 8-cell rates (37.45 ± 2.21% vs. 47.09 ± 1.38%; P < 0.01) and blastocyst rates of Si-METTL3 (12.17% ± 2.84 vs. 20.83 ± 3.61%; P < 0.01) in Si-METTL3 group were significantly decreased compared with that of control under hypoxic conditions, significant changes were found in the m6A-related genes and the expression levels of critical transcription factors, such as, NANOG, GATA3, CDX2 and SOX17, were decreased. This study revealed the key role of METTL3 in the regulation of embryonic development under oxidative stress, and laid the foundation for further study of the crucial mechanism of oxidative stress during the early embryonic development of goats.