FTO Knockout Causes Chromosome Instability and G2/M Arrest in Mouse GC-1 Cells

Dynamic RNA methylation modifications and their regulatory role in mammalian development and diseases

Among over 170 different types of chemical modifications on RNA nucleobases identified so far, RNA methylation is the major type of epitranscriptomic modifications existing on almost all types of RNAs, and has been demonstrated to participate in the entire process of RNA metabolism, including transcription, pre-mRNA alternative splicing and maturation, mRNA nucleus export, mRNA degradation and stabilization, mRNA translation. Attributing to the development of high-throughput detection technologies and the identification of both dynamic regulators and recognition proteins, mechanisms of RNA methylation modification in regulating the normal development of the organism as well as various disease occurrence and developmental abnormalities upon RNA methylation dysregulation have become increasingly clear. Here, we particularly focus on three types of RNA methylations: N6-methylcytosine (m6A), 5-methylcytosine (m5C), and N7-methyladenosine (m7G). We summarize the elements related to their dynamic installment and removal, specific binding proteins, and the development of high-throughput detection technologies. Then, for a comprehensive understanding of their biological significance, we also overview the latest knowledge on the underlying mechanisms and key roles of these three mRNA methylation modifications in gametogenesis, embryonic development, immune system development, as well as disease and tumor progression.

[The Roles of N6-Methyladenosine Modification and Its Regulators in Male Reproduction]

Infertility affects an estimated 10 to 15 percent of couples worldwide, with approximately half of the cases attributed to male-related issues. Most men diagnosed with infertility exhibit symptoms such as oligospermia, asthenospermia, azoospermia, and compromised sperm quality. Spermatogenesis is a complex and tightly coordinated process of germ cell differentiation, precisely regulated at transcriptional, posttranscriptional, and translational levels to ensure stage-specific gene expression during the development of spermatogenic cells and normal spermiogenesis. N6-methyladenosine (m6A) stands out as the most prevalent modification on eukaryotic mRNA, playing pivotal roles in various biological processes, including mRNA splicing, transportation, and translation. RNA methylation modification is a dynamic and reversible process primarily mediated by "writers", removed by "erasers", and recognized by "readers". In mammals, the aberrant methylation modification of m6A on mRNA is associated with a variety of diseases, including male infertility. However, the precise involvement of disrupted m6A modification in the pathogenesis of human male infertility remains unresolved. Intriguingly, a significant correlation has been found between the expression levels of m6A regulators in the testis and the severity of sperm concentration, motility, and morphology. Aberrant expression patterns of m6A regulatory proteins have been detected in anomalous human semen samples, including those of oligospermia, asthenozoospermia, and azoospermia. Furthermore, the examination of both sperm samples and testicular tissues revealed abnormal mRNA m6A modification, leading to reduced sperm motility and concentration in infertile men. Consequently, it is hypothesized that dysregulation of m6A modification might serve as an integral link in the mechanism of male infertility. This paper presents a comprehensive review of the recent discoveries regarding the spatial and temporal expression dynamics of m6A regulators in testicular tissues and the correlation between deregulated m6A regulators and human male infertility. Previous studies predominantly utilized constitutive or conditional knockout animal models for testicular phenotypic investigations. However, gene suppression in additional tissues could potentially influence the testis in constitutive knockout models. Furthermore, considering the compromised spermatogenesis observed in constitutive animals, distinguishing between the indirect effects of gene depletion on testicular development and its direct impact on the spermatogenic process is challenging, due to their intricate relationship. Such confounding factors might compromise the validity of the findings. To address this challenge, an inducible and conditional gene knockout model may serve as a superior approach. To date, nearly all reported studies have concentrated solely on the level changes of m6A and its regulators in germs cells, while the understanding of the function of m6A modification in testicular somatic cells remains limited. Testicular somatic cells, including peritubular myoid cells, Sertoli cells, and Leydig cells, play indispensable roles during spermatogenesis. Hence, comprehensive exploration of m6A modification within these cells as an additional crucial regulatory mechanism is warranted. In addition, exploration into the presence of unique methylation mechanisms or m6A regulatory factors within the testes is warranted. To elucidate the role of m6A modification in germ cells and testicular somatic cells, detailed experimental strategies need to be implemented. Among them, manipulation of the levels of key enzymes involved in m6A methylation and demethylation might be the most effective approach. Moreover, comprehensive analysis of the gene expression profiles involved in various signaling pathways, such as Wnt/β-catenin, Ras/MAPK, and Hippo, in m6A-modified germ cells and testicular somatic cells can provide more insight into its regulatory role in the spermatogenesis process. Further research in this area could provide valuable insights for developing innovative strategies to treat male infertility. Finally, considering the mitigation impact of m6A imbalance regulation on disease, investigation concerning whether restoring the equilibrium of m6A modification regulation can restore normal spermatogenesis function is essential, potentially elucidating the pivotal clinical significance of m6A modulation in male infertility.

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.

Role of N6-methyladenosine modification in central nervous system diseases and related therapeutic agents

N6-methyladenosine (m6A) is a ubiquitous mRNA modification in eukaryotes. m6A occurs through the action of methyltransferases, demethylases, and methylation-binding proteins. m6A methylation of RNA is associated with various neurological disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), depression, cerebral apoplexy, brain injury, epilepsy, cerebral arteriovenous malformations, and glioma. Furthermore, recent studies report that m6A-related drugs have attracted considerable concerns in the therapeutic areas of neurological disorders. Here, we mainly summarized the role of m6A modification in neurological diseases and the therapeutic potential of m6A-related drugs. The aim of this review is expected to be useful to systematically assess m6A as a new potential biomarker and develop innovative modulators of m6A for the amelioration and treatment of neurological disorders.

Fat mass and obesity-associated factor (FTO)-mediated N6-methyladenosine regulates spermatogenesis in an age-dependent manner

N6-methyladenosine (m6A) is the most prevalent reversible RNA modification in the mammalian transcriptome. It has recently been demonstrated that m6A is crucial for male germline development. Fat mass and obesity-associated factor (FTO), a known m6A demethylase, is widely expressed in human and mouse tissues and is involved in manifold biological processes and human diseases. However, the function of FTO in spermatogenesis and male fertility remains poorly understood. Here, we generated an Fto knockout mouse model using CRISPR/Cas9-mediated genome editing techniques to address this knowledge gap. Remarkably, we found that loss of Fto in mice caused spermatogenesis defects in an age-dependent manner, resulting from the attenuated proliferation ability of undifferentiated spermatogonia and increased male germ cell apoptosis. Further research showed that FTO plays a vital role in the modulation of spermatogenesis and Leydig cell maturation by regulating the translation of the androgen receptor in an m6A-dependent manner. In addition, we identified two functional mutations of FTO in male infertility patients, resulting in truncated FTO protein and increased m6A modification in vitro. Our results highlight the crucial effects of FTO on spermatogonia and Leydig cells for the long-term maintenance of spermatogenesis and expand our understanding of the function of m6A in male fertility.

Comprehensive analysis of long non-coding RNA expression profiles of GC-1spg cells with m6A methylation knockdown

Spermatogenesis is a complex process that requires many regulatory mechanisms to form healthy sperm. Numerous studies have also proved that m6A methylation modification and lncRNA are essential for normal spermatogenesis. However, the mutual regulation of m6A methylation and lncRNA in spermatogenesis is still unclear. In this study, we knocked down METTL3 in GC-1spg cells and found that a reduction in METTL3 increased cell proliferation. Further, we examined the lncRNA expression profiles of normal spermatogonia and spermatogonia with knocked down METTL3. We detected 30,924 lncRNAs, of which 34 were up-regulated and 77 down-regulated. The results of the MeRIP-qPCR experiment showed that ENSMUST00000186472, MSTRG.8019.3 and ENSMUST00000202148 had m6A methylation sites and were regulated by METTL3. We constructed ceRNA networks for these 3 lncRNAs. And we identified that these 3 lncRNAs might act as miRNA sponges to regulate some genes related to spermatogenesis. This study focuses on exploring the regulatory mechanisms of m6A methylation on lncRNAs in spermatogonia and provides some epigenetic theories for subsequent studies on the expression mechanisms of lncRNAs.

FTO regulates the DNA damage response via effects on cell-cycle progression

The fat mass and obesity-associated protein FTO is an "eraser" of N6-methyladenosine, the most abundant mRNA modification. FTO plays important roles in tumorigenesis. However, its activities have not been fully elucidated and its possible involvement in DNA damage - the early driving event in tumorigenesis - remains poorly characterized. Here, we have investigated the role of FTO in the DNA damage response (DDR) and its underlying mechanisms. We demonstrate that FTO responds to various DNA damage stimuli. FTO is overexpressed in mice following exposure to the promutagens aristolochic acid I and benzo[a]pyrene. Knockout of the FTO gene in TK6 cells, via CRISPR/Cas9, increased genotoxicity induced by DNA damage stimuli (micronucleus and TK mutation assays). Cisplatin- and diepoxybutane-induced micronucleus frequencies and methyl methanesulfonate- and azathioprine-induced TK mutant frequencies were also higher in FTO KO cells. We investigated the potential roles of FTO in DDR. RNA sequencing and enrichment analysis revealed that FTO deletion disrupted the p38 MAPK pathway and inhibited the activation of nucleotide excision repair and cell-cycle-related pathways following cisplatin (DNA intrastrand cross-links) treatment. These effects were confirmed by western blotting and qRT-PCR. FTO deletion impaired cell-cycle arrest at the G2/M phase following cisplatin and diepoxybutane treatment (flow cytometry analysis). Our findings demonstrated that FTO is involved in several aspects of DDR, acting, at least in part, by impairing cell cycle progression.

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.

The role of demethylase AlkB homologs in cancer

The AlkB family (ALKBH1-8 and FTO), a member of the Fe (II)- and α-ketoglutarate-dependent dioxygenase superfamily, has shown the ability to catalyze the demethylation of a variety of substrates, including DNA, RNA, and histones. Methylation is one of the natural organisms’ most prevalent forms of epigenetic modifications. Methylation and demethylation processes on genetic material regulate gene transcription and expression. A wide variety of enzymes are involved in these processes. The methylation levels of DNA, RNA, and histones are highly conserved. Stable methylation levels at different stages can coordinate the regulation of gene expression, DNA repair, and DNA replication. Dynamic methylation changes are essential for the abilities of cell growth, differentiation, and division. In some malignancies, the methylation of DNA, RNA, and histones is frequently altered. To date, nine AlkB homologs as demethylases have been identified in numerous cancers’ biological processes. In this review, we summarize the latest advances in the research of the structures, enzymatic activities, and substrates of the AlkB homologs and the role of these nine homologs as demethylases in cancer genesis, progression, metastasis, and invasion. We provide some new directions for the AlkB homologs in cancer research. In addition, the AlkB family is expected to be a new target for tumor diagnosis and treatment.

Photoperiod alters testicular methyltransferase complex mRNA expression in Siberian hamsters

Exposure to long photoperiods stimulates, whereas exposure to short photoperiods transiently inhibit testicular function in Siberian hamsters via well-described neuroendocrine mechanisms. However, less is known about the intra-testicular regulation of these photoperiod-mediated changes. N6-methyladenosine (m6A) is one of the most common mRNA modifications in eukaryotes, with alterations in m6A mRNA methylation affecting testis function and fertility. We hypothesized that genes controlling m6A methylation such as methyltransferase-like-3 (Mettl3) and -14 (Mettl14) and Wilms' tumor-1 associated protein (Wtap), part of an mRNA methylating methyl-transferase complex, or the fat-mass-and-obesity-associated (Fto) and the α-ketoglutarate-dependent dioxygenase alkB homolog-5 (Alkbh5) genes responsible for m6A demethylation, may be differentially regulated by photoperiod in the testis. Male hamsters were exposed to long (LD, control) photoperiod for 14-weeks, short (SD) photoperiod for 2, 5, 8, 11 and 14-weeks to induce regression, or SD for 14-weeks followed by transfer to LD for 1, 2, 4 or 8-weeks to induce recrudescence (post-transfer, PT). SD exposure significantly reduced body, testis, and epididymal masses compared to all other groups. Spermatogenic index, seminiferous tubule diameters and testosterone concentrations significantly decreased in SD as compared to LD, returning to levels no different than LD in post-transfer groups. SD exposure significantly decreased Wtap, Fto, Alkbh5, but increased Mettl14 mRNA expression as compared to LD, with values in PT groups restored to LD levels. Mettl3 mRNA expression did not change. These results suggest that testicular recovery induced by stimulatory photoperiod is relatively rapid, and that the methyltransferase complex may play a role during photostimulated testicular recrudescence.

Prognostic value of m6A regulators and the nomogram construction in glioma patients

Although N6-methyladenosine (m6A) has been implicated in various biological functions in human cancers, its role in predicting the prognosis of glioma remains unclear. In this study, the transcriptome expression profiles and the clinical data of 961 patients were derived from the Chinese Glioma Genome Atlas (CGGA). We comprehensively evaluated the association between the expression of m6A regulators and the prognosis of glioma and established a 3-gene (YTHDF2, FTO, and ALKBH5) risk signature using least absolute shrinkage and selection operator (LASSO) analysis. Patients with a high-risk signature had significantly adverse prognoses. Gene set enrichment analysis (GSEA) analysis revealed that the G2M checkpoint, MTORC1 signaling, epithelial mesenchymal transition, and PI3K-AKT-mTOR signaling were significantly enriched in the high-risk group. Univariate and multivariate Cox regression analyses confirmed the independent prognostic value of this risk signature. We then constructed a nomogram for individualized prediction of overall survival (OS) by integrating clinicopathological features (age, World Health Organization [WHO] grade), treatment information (radiotherapy, temozolomide therapy), and m6A risk signature. The calibration curves showed excellent agreement between the predicted and actual probabilities for the 1-, 3-, and 5-year OS, with a C-index of 0.780 in the training cohort and 0.717 in the validation cohort. Altogether, our study elucidated the important role of m6A regulators in glioma prognosis, which is valuable for the selection of therapeutic methods and clinical management of patients with glioma.

Application of CRISPR/Cas Technology in Spermatogenesis Research and Male Infertility Treatment

As the basis of animal reproductive activity, normal spermatogenesis directly determines the efficiency of livestock production. An in-depth understanding of spermatogenesis will greatly facilitate animal breeding efforts and male infertility treatment. With the continuous development and application of gene editing technologies, they have become valuable tools to study the mechanism of spermatogenesis. Gene editing technologies have provided us with a better understanding of the functions and potential mechanisms of action of factors that regulate spermatogenesis. This review summarizes the applications of gene editing technologies, especially CRISPR/Cas9, in deepening our understanding of the function of spermatogenesis-related genes and disease treatment. The problems of gene editing technologies in the field of spermatogenesis research are also discussed.

ALKBH5 regulates somatic cell reprogramming in a phase specific manner

Establishment of the pluripotency regulatory network in somatic cells by introducing four transcription factors (octamer binding transcription factor 4 (OCT4), sex determining region Y (SRY)-box 2 (SOX2), Kruppel-like factor 4 (KLF4), and cellular myelocytomatosis (c-MYC)) provides a promising tool for cell-based therapies in regenerative medicine. Nevertheless, the mechanisms at play when generating induced pluripotent stem cells from somatic cells are only partly understood. Here, we show that the RNA specific N6-methyladenosine (m6A) demethylase ALKBH5 regulates somatic cell reprogramming in a stage-specific manner through its catalytic activity. Knockdown or knockout of Alkbh5 in the early reprogramming phase impairs reprogramming efficiency by reducing the proliferation rate through arresting the cells at G2/M phase and decreasing the upregulation of epithelial markers. On the other hand, ALKBH5 overexpression at the early reprogramming phase has no significant impact on reprogramming efficiency, while overexpression at the late phase enhances reprogramming by stabilizing Nanog transcripts, resulting in upregulated Nanog expression. Our study provides mechanistic insight into the crucial dynamic role of ALKBH5 through its catalytic activity in regulating somatic cell reprogramming at the posttranscriptional level.

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.

Identification and Validation of a Prognostic Prediction Model of m6A Regulator-Related LncRNAs in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a highly invasive malignancy prone to recurrence, and patients with HCC have a low 5-year survival rate. Long non-coding RNAs (lncRNAs) play a vital role in the occurrence and development of HCC. N6-methyladenosine methylation (m6A) is the most common modification influencing cancer development. Here, we used the transcriptome of m6A regulators and lncRNAs, along with the complete corresponding clinical HCC patient information obtained from The Cancer Genome Atlas (TCGA), to explore the role of m6A regulator-related lncRNA (m6ARlnc) as a prognostic biomarker in patients with HCC. The prognostic m6ARlnc was selected using Pearson correlation and univariate Cox regression analyses. Moreover, three clusters were obtained via consensus clustering analysis and further investigated for differences in immune infiltration, immune microenvironment, and prognosis. Subsequently, nine m6ARlncs were identified with Lasso-Cox regression analysis to construct the prognostic signature m6A-9LPS for patients with HCC in the training cohort (n = 226). Based on m6A-9LPS, the risk score for each case was calculated. Patients were then divided into high- and low-risk subgroups based on the cutoff value set by the X-tile software. m6A-9LPS showed a strong prognosis prediction ability in the validation cohort (n = 116), the whole cohort (n = 342), and even clinicopathological stratified survival analysis. Combining the risk score and clinical characteristics, we established a nomogram for predicting the overall survival (OS) of patients. To further understand the mechanism underlying the m6A-9LPS-based classification of prognosis differences, KEGG and GO enrichment analyses, competitive endogenous RNA (ceRNA) network, chemotherapeutic agent sensibility, and immune checkpoint expression level were assessed. Taken together, m6A-9LPS could be used as a precise prediction model for the prognosis of patients with HCC, which will help in individualized treatment of HCC.

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.

Increased m6A-RNA methylation and FTO suppression is associated with myocardial inflammation and dysfunction during endotoxemia in mice

Endotoxemia triggers life-threatening immune and cardiovascular response that leads to tissue damage, multi-organ failure, and death. The understanding of underlying molecular mechanisms is still evolving. N6-methyladenosine (m6A)-RNA modification plays key regulatory role in numerous biological processes. However, it remains unclear whether endotoxemia alters RNA methylation in the myocardium. In the current study, we investigated the effect of lipopolysaccharide (LPS)-induced endotoxemia on m6A-RNA methylation and its implications on myocardial inflammation and left ventricular (LV) function. Following LPS administration, mice showed increases in m6A-RNA methylation in the myocardium with a corresponding decrease in the expression of fat mass and obesity-associated protein (FTO, an m6A eraser/demethylase). The changes were associated with a significant increase in expression of myocardial inflammatory cytokine genes, such as IL-6, TNF-α, IL-1β, and reduced LV function. Moreover, rat cardiomyoblasts (H9c2) exposed to LPS showed similar changes (with increase in m6A-RNA methylation and inflammatory cytokine genes, whereas downregulation of FTO). Furthermore, methylated RNA immunoprecipitation assay showed hypermethylation and increase in the expression of IL-6 and TNF-α genes in LPS-treated H9c2 cells as compared to untreated cells. Interestingly, FTO knockdown in cardiomyocytes mimicked the above effects. Taken together, these data suggest that endotoxemia-induced m6A methylation might play a critical role in expression of cardiac proinflammatory cytokines, and modulation of m6A methylation might limit myocardial inflammation and dysfunction during endotoxemia.

The Latest Research Progress of m6A Modification and Its Writers, Erasers, Readers in Infertility: A Review

Eukaryotic messenger mRNAs contain many RNA methyl chemical modifications, in which N⁶-methyladenosine (m⁶A) plays a very important role. The modification process of RNA methylation is a dynamic reversible regulatory process that is mainly catalyzed by "Writer" m⁶A methyltransferase, removed by "Eraser" m⁶A demethylase, and recognized by the m⁶A binding protein, thereby, linking m⁶A modification with other mRNA pathways. At various stages of the life cycle, m⁶A modification plays an extremely important role in regulating mRNA splicing, processing, translation, as well as degradation, and is associated with gametogenesis and fertility for both sexes. Normal gametogenesis is a basic guarantee of fertility. Infertility leads to trauma, affects harmony in the family and seriously affects the quality of life. We review the roles and mechanisms of RNA m⁶A methylation modification in infertility and provide a potential target for infertility treatment, which can be used for drug development.

Emerging Role of m6 A Methylome in Brain Development: Implications for Neurological Disorders and Potential Treatment

Dynamic modification of RNA affords proximal regulation of gene expression triggered by non-genomic or environmental changes. One such epitranscriptomic alteration in RNA metabolism is the installation of a methyl group on adenosine [N⁶-methyladenosine (m⁶A)] known to be the most prevalent modified state of messenger RNA (mRNA) in the mammalian cell. The methylation machinery responsible for the dynamic deposition and recognition of m⁶A on mRNA is composed of subunits that play specific roles, including reading, writing, and erasing of m⁶A marks on mRNA to influence gene expression. As a result, peculiar cellular perturbations have been linked to dysregulation of components of the mRNA methylation machinery or its cofactors. It is increasingly clear that neural tissues/cells, especially in the brain, make the most of m⁶A modification in maintaining normal morphology and function. Neurons in particular display dynamic distribution of m⁶A marks during development and in adulthood. Interestingly, such dynamic m⁶A patterns are responsive to external cues and experience. Specific disturbances in the neural m⁶A landscape lead to anomalous phenotypes, including aberrant stem/progenitor cell proliferation and differentiation, defective cell fate choices, and abnormal synaptogenesis. Such m⁶A-linked neural perturbations may singularly or together have implications for syndromic or non-syndromic neurological diseases, given that most RNAs in the brain are enriched with m⁶A tags. Here, we review the current perspectives on the m⁶A machinery and function, its role in brain development and possible association with brain disorders, and the prospects of applying the clustered regularly interspaced short palindromic repeats (CRISPR)–dCas13b system to obviate m⁶A-related neurological anomalies.

Prognostic and clinicopathological value of BUB1B expression in patients with lung adenocarcinoma: a meta-analysis

BACKGROUND

Abnormal BUB1B expression has been proven to be related to the poor prognosis of various tumors. This meta-analysis aimed to identify the prognostic role of BUB1B in patients with lung adenocarcinoma (LUAD).

RESEARCH DESIGN AND METHODS

Relevant studies from the PubMed, Embase, Web of Science, and Cochrane Library databases and two public databases that stored sequencing data were retrieved. The standardized mean difference (SMD) and 95% confidence intervals (CIs) for the association between the BUB1B expression level and clinical characteristics were calculated. Pooled hazard ratios (HRs) and 95% CIs were calculated to estimate the association between BUB1B expression and survival outcomes.

RESULTS

A total of 16 studies involving 2771 LUAD patients with BUB1B expression were included in this meta-analysis. Patients with older age showed low BUB1B expression. High BUB1B expression was associated with male sex, a smoking history, and an advanced TNM stage. High BUB1B expression was predictive of poor overall survival (OS) and progression-free survival (PFS). In addition, no publication bias was found.

CONCLUSIONS

This meta-analysis demonstrates that BUB1B is a significant biomarker for a poor prognosis and poor clinicopathological outcomes in patients with LUAD.

Epigenetic regulation of mRNA N6-methyladenosine modifications in mammalian gametogenesis

N6-methyladenosine (m6A) is the most prevalent epigenetic modification of mRNAs and broadly influences various biological processes by regulating post-transcriptional gene expression in eukaryotes. The reversible m6A modification is catalyzed by methyltransferases, METTL3 and METTL14 (writers), removed by the demethylases FTO and ALKBH5 (erasers) and recognized by m6A-binding proteins, namely the YTH domain-containing family of proteins (readers). Both m6A modification and the related enzymes are involved in the regulation of normal gametogenesis and embryonic development in many species. Recent studies showed that loss of m6A compromises gamete maturation, sex hormone synthesis, fertility and early embryonic development. In this review, we have summarized the most recent findings on the role of mRNA m6A modification in mammalian gametogenesis to emphasize the epigenetic regulation of mRNA in the reproductive system.

A five-m6A regulatory gene signature is a prognostic biomarker in lung adenocarcinoma patients

We analyzed the prognostic value of N6-methyladenosine (m6A) regulatory genes in lung adenocarcinoma (LADC) and their association with tumor immunity and immunotherapy response. Seventeen of 20 m6A regulatory genes were differentially expressed in LDAC tissue samples from the TCGA and GEO databases. We developed a five-m6A regulatory gene prognostic signature based on univariate and Lasso Cox regression analysis. Western blot analysis confirmed that the five prognostic m6A regulatory proteins were highly expressed in LADC tissues. We constructed a nomogram with five-m6A regulatory gene prognostic risk signature and AJCC stages. ROC curves and calibration curves showed that the nomogram was well calibrated and accurately distinguished high-risk and low-risk LADC patients. Weighted gene co-expression analysis showed significant correlation between prognostic risk signature genes and the turquoise module enriched with cell cycle genes. The high-risk LADC patients showed significantly higher PD-L1 levels, increased tumor mutational burden, and a lower proportion of CD8+ T cells in the tumor tissues and improved response to immune checkpoint blockade therapy. These findings show that this five-m6A regulatory gene signature is a prognostic biomarker in LADC and that immune checkpoint blockade is a potential therapeutic option for high-risk LADC patients.

RNA N6-methyladenosine modification, spermatogenesis, and human male infertility

RNA N6-methyladenosine (m6A) modification is one of the main forms of posttranscriptional modification, and its dysregulation is involved in a series of pathological processes. RNA m6A regulators, which mediate dynamic RNA m6A modification, are expressed in almost all types of testicular cells, including spermatogenetic cells and somatic cells. Cumulative studies have found that knockout of RNA m6A regulators in the testis leads to abnormal metabolism of the target mRNAs, which eventually causes spermatogenetic disorders and infertility. To date, a role for dysregulated RNA m6A modification in human male infertility remains elusive; however, dysregulated expression of RNA m6A regulators in abnormal human semen samples, including oligospermia, asthenozoospermia and azoospermia, has been found. Therefore, we speculate that abnormal RNA m6A methylation may be an important mechanism of male infertility. In this review, we summarize the recent findings regarding the spatiotemporal expression of RNA m6A regulators in the testes, mechanisms of RNA m6A modification in spermatogenesis and the relation between dysregulated RNA m6A regulators and human male infertility. In addition, we also discuss future directions in studying the molecular mechanism of male infertility and exploring their clinical applications from the viewpoint of RNA m6A modification.

Fumonisin B1 alters global m6A RNA methylation and epigenetically regulates Keap1-Nrf2 signaling in human hepatoma (HepG2) cells

FB₁ is a common contaminant of cereal grains that affects human and animal health. It has become increasingly evident that epigenetic changes are implicated in FB₁ toxicity. N6-methyladenosine (m6A), the most abundant post-transcriptional RNA modification, is influenced by fluctuations in redox status. Since oxidative stress is a characteristic of FB₁ exposure, we determined if there is cross-talk between oxidative stress and m6A in FB₁-exposed HepG2 cells. Briefly, HepG2 cells were treated with FB₁ (0, 5, 50, 100, 200 µM; 24 h) and ROS, LDH and m6A levels were quantified. qPCR was used to determine the expression of m6A modulators, Nrf2, Keap1 and miR-27b, while western blotting was used to quantify Keap1 and Nrf2 protein expression. Methylation status of Keap1 and Nrf2 promoters was assessed and RNA immunoprecipitation quantified m6A-Keap1 and m6A-Nrf2 levels. FB₁ induced accumulation of intracellular ROS (p ≤ 0.001) and LDH leakage (p ≤ 0.001). Elevated m6A levels (p ≤ 0.05) were accompanied by an increase in m6A "writers" [METLL3 (p ≤ 0.01) and METLL14 (p ≤ 0.01)], and "readers" [YTHDF1 (p ≤ 0.01), YTHDF2 (p ≤ 0.01), YTHDF3 (p ≤ 0.001) and YTHDC2 (p ≤ 0.01)] and a decrease in m6A "erasers" [ALKBH5 (p ≤ 0.001) and FTO (p ≤ 0.001)]. Hypermethylation and hypomethylation occurred at Keap1 (p ≤ 0.001) and Nrf2 (p ≤ 0.001) promoters, respectively. MiR-27b was reduced (p ≤ 0.001); however, m6A-Keap1 (p ≤ 0.05) and m6A-Nrf2 (p ≤ 0.01) levels were upregulated. This resulted in the ultimate decrease in Keap1 (p ≤ 0.001) and increase in Nrf2 (p ≤ 0.001) expression. Our findings reveal that m6A RNA methylation can be modified by exposure to FB₁, and a cross-talk between m6A and redox regulators does occur.

Aberrant regulation of RNA methylation during spermatogenesis

Natural modifications of cellular RNA include various chemical modifications, such as N6-methyladenosine (m⁶ A), which enable the orderly metabolism and function of RNA structural diversity, thereby affecting gene expression. Spermatogenesis is a complex differentiating developmental process, which includes the proliferation of spermatogonial stem cells, spermatocyte meiosis and sperm maturation. Emerging evidence has shown that RNA methylation can influence RNA splicing, exportation and translation, which are controlled in the male germline in order to ensure coordinated gene expression. In this review, we summarize the typical characteristics of different types of RNA methylation during the process of spermatogenesis. In particular, we emphasize the functions of the RNA methylation effectors during the male germ cell development.

Therapeutic potential of ALKB homologs for cardiovascular disease

Cardiovascular diseases (CVDs) are the leading causes of human death. Recently, ALKB homologs, including ALKBH1-8 and FTO, have been found to have a variety of biological functions, such as histone demethylation, RNA demethylation, and DNA demethylation. These functions may regulate the physiological and pathological processes of CVDs, including inflammation, oxidative stress, cell apoptosis, and mitochondrial, endothelial, and fat metabolism dysfunction. In the present review, we summarize the biological functions of ALKB homologs and the relationship between the ALKB homologs and CVDs. Importantly, we discuss the roles of ALKB homologs in the regulation of oxidative stress, inflammation, autophagy, and DNA damage in CVDs, as well as the practical applications of ALKB homologs inhibitors or agonists in treating CVDs. In conclusion, the ALKBH family might be a promising target for CVDs therapy.

Principles of RNA methylation and their implications for biology and medicine

RNA methylation is a post-transcriptional level of regulation. At present, more than 150 kinds of RNA modifications have been identified. They are widely distributed in messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA), noncoding small RNA (sncRNA) and long-chain non-coding RNA (lncRNA). In recent years, with the discovery of RNA methylation related proteins and the development of high-throughput sequencing technology, the mystery of RNA methylation has been gradually revealed, and its biological function and application value have gradually emerged. In this review, a large number of research results of RNA methylation in recent years are collected. Through systematic summary and refinement, this review introduced RNA methylation modification-related proteins and RNA methylation sequencing technologies, as well as the biological functions of RNA methylation, expressions and applications of RNA methylation-related genes in physiological or pathological states such as cancer, immunity and virus infection, and discussed the potential therapeutic strategies.

Fat mass and obesity-associated protein promotes the tumorigenesis and development of liver cancer

Liver cancer is the fourth leading cause of cancer-associated mortality worldwide. Statistics indicate that the incidence of liver cancer has been increasing and that its prognosis remains poor. Fat mass and obesity-associated protein (FTO) is a demethylase that is involved in N6-methyladenosine (m6a) RNA modification; however, to the best of our knowledge, its role in tumorigenesis and development of liver cancer remains unknown. In the present study, cell proliferation, colony formation, apoptosis, Transwell and wound healing assays of small interfering (si)RNA-FTO HepG2 cells were performed, and the levels of m6A RNA methylation were assessed. Additionally, the prognostic value of FTO in liver cancer was analyzed using immunohistochemistry analysis. The results from the EpiQuik m6A RNA methylation quantitative assay revealed that knockdown of FTO increased the total m6A methylation level. Notably, FTO promoted the proliferation and migration of liver cancer cells. Additionally, FTO expression was upregulated in patients with liver cancer and was associated with a high Edmondson Grade, which served as an independent prognostic factor for liver cancer. Results from the Kaplan-Meier survival analysis revealed that low expression levels of FTO predicted a good prognosis. The 5-year overall survival of the low FTO expression group was 68% compared with 48% in the high FTO expression group (P=0.077). In conclusion, the present study suggested that FTO regulates the tumorigenesis and development of liver cancer.

In Vitro Cytotoxicity Effects of Zinc Oxide Nanoparticles on Spermatogonia Cells

Zinc Oxide Nanoparticles (ZnO NPs) are a type of metal oxide nanoparticle with an extensive use in biomedicine. Several studies have focused on the biosafety of ZnO NPs, since their size and surface area favor entrance and accumulation in the body, which can induce toxic effects. In previous studies, ZnO NPs have been identified as a dose- and time-dependent cytotoxic inducer in testis and male germ cells. However, the consequences for the first cell stage of spermatogenesis, spermatogonia, have never been evaluated. Therefore, the aim of the present work is to evaluate in vitro the cytotoxic effects of ZnO NPs in spermatogonia cells, focusing on changes in cytoskeleton and nucleoskeleton. For that purpose, GC-1 cell line derived from mouse testes was selected as a model of spermatogenesis. These cells were treated with different doses of ZnO NPs for 6 h and 12 h. The impact of GC-1 cells exposure to ZnO NPs on cell viability, cell damage, and cytoskeleton and nucleoskeleton dynamics was assessed. Our results clearly indicate that higher concentrations of ZnO NPs have a cytotoxic effect in GC-1 cells, leading to an increase of intracellular Reactive Oxygen Species (ROS) levels, DNA damage, cytoskeleton and nucleoskeleton dynamics alterations, and consequently cell death. In conclusion, it is here reported for the first time that ZnO NPs induce cytotoxic effects, including changes in cytoskeleton and nucleoskeleton in mouse spermatogonia cells, which may compromise the progression of spermatogenesis in a time- and dose-dependent manner.