FTO regulates myoblast proliferation by controlling CCND1 expression in an m6A-YTHDF2-dependent manner

Effects of PPARG on the proliferation, apoptosis, and estrogen secretion in goat granulosa cells

As a member of peroxisome proliferator-activated receptor (PPAR) family, PPARG has been reported to be involved in glucolipid metabolism in various species. However, the function of PPARG in estradiol (E2) synthesis, apoptosis, and proliferation in goat ovarian granulosa cells (GCs) is unclear. In this study, we found that goat PPARG was expressed in GCs of all grades of follicles, and localized in the cytoplasm and nucleus of GCs. Transfection of small interfering RNA-PPARG2 (si-PPARG2) decreased E2 synthesis and the abundances of HSD3B and CYP19A1 mRNA and protein. It also promoted cell apoptosis with significant increases in the ratio of BAX/BCL-2 and Caspase3 mRNA and protein. Meanwhile, cell cycle was inhibited by si-PPARG2 transfection, accompanied by decreased mRNA levels of CDK4, CKD6, MYC, CCND1, CCND2, PCNA, and CCNB, increased mRNA level of P53, and decreased protein levels of CDK4, MYC, and CCND1. Furthermore, PPARG interference affected the mRNA and protein abundances of CREB as well as the phosphorylation of CREB but not PKA. In conclusion, our data suggest that PPARG plays an important role in regulating E2 synthesis, cell apoptosis, and proliferation of goat GCs, including the CREB expression and phosphorylation. These results provide evidences for the in-depth study of PPARG in the regulation of goat GCs function.

Identification of key lncRNAs and mRNAs in muscle development pathways of Tan sheep

The study aimed to identify the long noncoding RNA (lncRNA) responsible for regulating muscle development in Tan sheep. RNA-seq analysis was conducted on longissimus dorsi samples from 1-day-old and 60-day-old Tan sheep to investigate the molecular processes involved in muscle development. A total of 5517 lncRNAs and 2885 mRNAs were found to be differentially expressed in the 60-day-old Tan sheep. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that these differentially expressed lncRNAs and mRNAs were linked to pathways crucial for muscle development, such as MAPK, cAMP, and calcium-mediated signaling pathways. Key genes like CDKN1A, MAPK14, TGFB1, MEF2C, MYOD1, and CD53 were identified as significant players in muscle development. The study validated the RNA-seq results through RT-qPCR, confirming the consistency of expression levels of differentially expressed lncRNAs and mRNAs. These findings indicate that lncRNA-mRNA networks produce a remarked effect on modulating muscle development in Tan sheep, such as lncRNAs (MSTRG.12808.1/MSTRG.22662.3/MSTRG.18310.1) and mRNAs (MSTRG.10027/MSTRG.10029/MSTRG.10258/MSTRG.11011/MSTRG.10354), laying the groundwork for future research in this area.

Fat Mass- and Obesity-Associated Protein (FTO) Promotes the Proliferation of Goat Skeletal Muscle Satellite Cells by Stabilizing DAG1 mRNA in an IGF2BP1-Related m6A Manner

Skeletal muscle development is spotlighted in mammals since it closely relates to animal health and economic benefits to the breeding industry. Researchers have successfully unveiled many regulatory factors and mechanisms involving myogenesis. However, the effect of N6-methyladenosine (m6A) modification, especially demethylase and its regulated genes, on muscle development remains to be further explored. Here, we found that the typical demethylase FTO (fat mass- and obesity-associated protein) was highly enriched in goats' longissimus dorsi (LD) muscles. In addition, the level of m6A modification on transcripts was negatively regulated by FTO during the proliferation of goat skeletal muscle satellite cells (MuSCs). Moreover, a deficiency of FTO in MuSCs significantly retarded their proliferation and promoted the expression of dystrophin-associated protein 1 (DAG1). m6A modifications of DAG1 mRNA were efficiently altered by FTO. Intriguingly, the results of DAG1 levels and its m6A enrichment from FB23-2 (FTO demethylase inhibitor)-treated cells were consistent with those of the FTO knockdown, indicating that the regulation of FTO on DAG1 depended on m6A modification. Further experiments showed that interfering FTO improved m6A modification at site DAG1-122, recognized by Insulin-like growth factor 2 mRNA-binding protein 1 (IGF2BP1) and consequently stabilized DAG1 transcripts. Our study suggests that FTO promotes the proliferation of MuSCs by regulating the expression of DAG1 through m6A modification. This will extend our knowledge of the m6A-related mechanism of skeletal muscle development in animals.

N-acetylcysteine stimulates the proliferation and differentiation in heat-stressed skeletal muscle cells

N-acetylcysteine (NAC) is known for its beneficial effects on health due to its antioxidant and antiapoptotic properties. This study explored the protective effects of NAC against oxidative stress in heat-stressed (HS) skeletal muscle cells and its role in promoting muscle development. NAC reduced the heat shock response by decreasing the expression of heat shock protein 70 (HSP70) in HS-induced muscle cells during proliferation and differentiation. NAC also mitigated HS-induced oxidative stress via increasing the antioxidant enzyme levels and reducing oxidant enzyme levels. Treatment with NAC at 2 mM increased cell viability from 43.68% ± 5.14%-66.69% ± 14.43% and decreased the apoptosis rate from 7.89% ± 0.53%-5.17% ± 0.11% in skeletal muscle cells. Additionally, NAC promoted the proliferation and differentiation of HS-induced skeletal muscle cells by upregulating the expression of PAX7, MYF5, MRF4 and MYHC. These findings suggest that NAC alleviates HS-induced oxidative damage in skeletal muscle cells and support muscle development.

Insights into the epitranscriptomic role of N6-methyladenosine on aging skeletal muscle

The modification of RNA through the N6-methyladenosine (m6A) has emerged as a growing area of research due to its regulatory role in gene expression and various biological processes regulating the expression of genes. m6A RNA methylation is a post-transcriptional modification that is dynamic and reversible and found in mRNA, tRNA, rRNA, and other non-coding RNA of most eukaryotic cells. It is executed by special proteins known as "writers," which initiate methylation; "erasers," which remove methylation; and "readers," which recognize it and regulate the expression of the gene. Modification by m6A regulates gene expression by affecting the splicing, translation, stability, and localization of mRNA. Aging causes molecular and cellular damage, which forms the basis of most age-related diseases. The decline in skeletal muscle mass and functionality because of aging leads to metabolic disorders and morbidities. The inability of aged muscles to regenerate and repair after injury poses a great challenge to the geriatric populace. This review seeks to explore the m6A epigenetic regulation in the myogenesis and regeneration processes in skeletal muscle as well as the progress made on the m6A epigenetic regulation of aging skeletal muscles.

N6-Methyladenosine Methylation of mRNA in Cell Apoptosis

Apoptosis, a highly controlled homeostatic mechanism that eliminates single cells without destroying tissue function, occurs during growing development and senescence. N6-methyladenosine (m6A), as the most common internal modification of eukaryotic mRNA, fine-tunes gene expression by regulating many aspects of mRNA metabolism, such as splicing, nucleation, stability, translation, and degradation. Remarkably, recent reports have indicated that aberrant methylation of m6A-related RNA may directly or indirectly influence the expression of apoptosis-related genes, thus regulating the process of cell apoptosis. In this review, we summarized the relationship between m6A modification and cell apoptosis, especially its role in the nervous system, and analyzed the limitations of the current research.

Comprehensive review on lipid metabolism and RNA methylation: Biological mechanisms, perspectives and challenges

Adipose tissue plays a crucial role in maintaining energy balance, regulating hormones, and promoting metabolic health. To address disorders related to obesity and develop effective therapies, it is essential to have a deep understanding of adipose tissue biology. In recent years, RNA methylation has emerged as a significant epigenetic modification involved in various cellular functions and metabolic pathways. Particularly in the realm of adipogenesis and lipid metabolism, extensive research is ongoing to uncover the mechanisms and functional importance of RNA methylation. Increasing evidence suggests that RNA methylation plays a regulatory role in adipocyte development, metabolism, and lipid utilization across different organs. This comprehensive review aims to provide an overview of common RNA methylation modifications, their occurrences, and regulatory mechanisms, focusing specifically on their intricate connections to fat metabolism. Additionally, we discuss the research methodologies used in studying RNA methylation and highlight relevant databases that can aid researchers in this rapidly advancing field.

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.

FTO demethylates regulates cell-cycle progression by controlling CCND1 expression in luteinizing goat granulosa cells

In mammals, N6-methyladenosine (m6A) stands out as one of the most abundant internal mRNA modifications and plays a crucial role in follicular development. Nonetheless, the precise mechanism by which the demethylase FTO regulates the progression of the goat luteinizing granulosa cells (LGCs) cycle remains to be elucidated. In our study, we primarily assessed the protein and mRNA expression levels of genes using Western blotting and quantitative real-time polymerase chain reaction (qRT-PCR), cell proliferation via EdU, cell viability with CCK-8, and apoptosis and cell cycle progression through flow cytometry. Here, the results demonstrated that knockdown of FTO significantly enhanced apoptosis, impeded cell proliferation, and increased autophagy levels in goat LGCs. Furthermore, the silencing of FTO substantially reduced cyclin D1 (CCND1) expression through the recognition and degradation of YTHDF2, consequently prolonging the cell cycle progression. This study sheds light on the mechanism by which FTO demethylation governs cell cycle progression by controlling the expression of CCND1 in goat LGCs, underscoring the dynamic role of m6A modification in the regulation of cell cycle progression.

Ythdf2-mediated STK11 mRNA decay supports myogenesis by inhibiting the AMPK/mTOR pathway

An emerging research focus is the role of m6A modifications in mediating the post-transcriptional regulation of mRNA during mammalian development. Recent evidence suggests that m6A methyltransferases and demethylases play critical roles in skeletal muscle development. Ythdf2 is a m6A "reader" protein that mediates mRNA degradation in an m6A-dependent manner. However, the specific function of Ythdf2 in skeletal muscle development and the underlying mechanisms remain unclear. Here, we observed that Ythdf2 expression was significantly upregulated during myogenic differentiation, whereas Ythdf2 knockdown markedly inhibited myoblast proliferation and differentiation. Combined analysis of high-throughput sequencing, Co-IP, and RIP assay revealed that Ythdf2 could bind to m6A sites in STK11 mRNA and form an Ago2 silencing complex to promote its degradation, thereby regulating its expression and consequently, the AMPK/mTOR pathway. Furthermore, STK11 downregulation partially rescued Ythdf2 knockdown-induced impairment of proliferation and myogenic differentiation by inhibiting the AMPK/mTOR pathway. Collectively, our results indicate that Ythdf2 mediates the decay of STK11 mRNA, an AMPK activator, in an Ago2 system-dependent manner, thereby driving skeletal myogenesis by suppressing the AMPK/mTOR pathway. These findings further enhance our understanding of the molecular mechanisms underlying RNA methylation in the regulation of myogenesis and provide valuable insights for conducting in-depth studies on myogenesis.

Targeted Demethylation of the TGFβ1 mRNA Promotes Myoblast Proliferation via Activating the SMAD2 Signaling Pathway

Recent evidence suggested that N6-methyladenosine (m6A) methylation can determine m6A-modified mRNA fate and play an important role in skeletal muscle development. It was well known that transforming growth factor beta 1 (TGFβ1) is involved in a variety of cellular processes, such as proliferation, differentiation, and apoptosis. However, little is known about the m6A-mediated TGFβ1 regulation in myogenesis. Here, we observed an increase in endogenous TGFβ1 expression and activity during myotube differentiation. However, the knockdown of TGFβ1 inhibits the proliferation and induces cell apoptosis of myoblast. Moreover, we found that m6A in 5′-untranslated regions (5′UTR) of TGFβ1 promote its decay and inhibit its expression, leading to the blockage of the TGFβ1/SMAD2 signaling pathway. Furthermore, the targeted specific demethylation of TGFβ1 m6A using dCas13b-FTO significantly increased the TGFβ1-mediated activity of the SMAD2 signaling pathway, promoting myoblast proliferation. These findings suggest that TGFβ1 is an essential regulator of myoblast growth that is negatively regulated by m6A. Overall, these results highlight the critical role of m6A-mediated post-transcriptional regulation in myogenesis.

Regulatory role of RNA N6-methyladenosine modifications during skeletal muscle development

Functional cells in embryonic myogenesis and postnatal muscle development undergo multiple stages of proliferation and differentiation, which are strict procedural regulation processes. N⁶-methyladenosine (m⁶A) is the most abundant RNA modification that regulates gene expression in specific cell types in eukaryotes and regulates various biological activities, such as RNA processing and metabolism. Recent studies have shown that m⁶A modification-mediated transcriptional and post-transcriptional regulation plays an essential role in myogenesis. This review outlines embryonic and postnatal myogenic differentiation and summarizes the important roles played by functional cells in each developmental period. Furthermore, the key roles of m⁶A modifications and their regulators in myogenesis were highlighted, and the synergistic regulation of m⁶A modifications with myogenic transcription factors was emphasized to characterize the cascade of transcriptional and post-transcriptional regulation during myogenesis. This review also discusses the crosstalk between m⁶A modifications and non-coding RNAs, proposing a novel mechanism for post-transcriptional regulation during skeletal muscle development. In summary, the transcriptional and post-transcriptional regulatory mechanisms mediated by m⁶A and their regulators may help develop new strategies to maintain muscle homeostasis, which are expected to become targets for animal muscle-specific trait breeding and treatment of muscle metabolic diseases.

N6-Methyladenosine RNA Modification: A Potential Regulator of Stem Cell Proliferation and Differentiation

Stem cell transplantation (SCT) holds great promise for overcoming diseases by regenerating damaged cells, tissues and organs. The potential for self-renewal and differentiation is the key to SCT. RNA methylation, a dynamic and reversible epigenetic modification, is able to regulate the ability of stem cells to differentiate and regenerate. N⁶-methyladenosine (m⁶A) is the richest form of RNA methylation in eukaryotes and is regulated by three classes of proteins: methyltransferase complexes, demethylase complexes and m⁶A binding proteins. Through the coordination of these proteins, RNA methylation precisely modulates the expression of important target genes by affecting mRNA stability, translation, selective splicing, processing and microRNA maturation. In this review, we summarize the most recent findings on the regulation of m⁶A modification in embryonic stem cells, induced pluripotent stem cells and adult stem cells, hoping to provide new insights into improving SCT technology.

Circular RNA circUSP13 sponges miR-29c to promote differentiation and inhibit apoptosis of goat myoblasts by targeting IGF1

Circular RNAs (circRNAs) are an indispensable element of post-transcriptional gene regulation, influencing a variety of biological processes including myogenic differentiation; however, little is known about the function of circRNA in goat myogenic differentiation. Using RNA-sequencing data from our laboratory, we explored the influences of circUSP13, as a candidate circRNA, on myoblast differentiation since its expression is higher in myoblasts of lamb (first day of age) than that of the fetus (75th day of pregnancy). In in vitro experiments, circUSP13 significantly promoted differentiation and inhibited apoptosis in goat primary myoblasts. Mechanistically, circUSP13 localized with miR-29c in the cytoplasm of goat myoblasts to regulate IGF1 expression. We further demonstrated that circUSP13 sponges miR-29c, promoting IGF1 expression that upregulated the expression of MyoG and MyHC. Thus, our results identified circUSP13 as a molecular marker for breeding programs of mutton production, as well as the circUSP13-miR-29c-IGF1 axis as a potential therapeutic target for combating muscle wasting.

FTO-mediated demethylation of GADD45B promotes myogenesis through the activation of p38 MAPK pathway

N6-methyladenosine (m⁶A) modification plays a critical role in mammalian development. However, the role of m⁶A in the skeletal muscle development remains largely unknown. Here, we report a global m⁶A modification pattern of goat skeletal muscle at two key development stages and identified that the m⁶A modification regulated the expression of the growth arrest and DNA damage-inducible 45B (GADD45B) gene, which is involved in myogenic differentiation. We showed that GADD45B expression increased during myoblast differentiation, whereas the downregulation of GADD45B inhibits myogenic differentiation and mitochondrial biogenesis. Moreover, the expression of GADD45B regulates the expression of myogenic regulatory factors and peroxisome proliferator-activated receptor gamma coactivator 1 alpha by activating the p38 mitogen-activated protein kinase (MAPK) pathway. Conversely, the inactivation of p38 MAPK abolished the GADD45B-mediated myogenic differentiation. Furthermore, we found that the knockdown of fat mass and obesity-associated protein (FTO) increases GADD45B m⁶A modification and decreases the stability of GADD45B mRNA, which impairs myogenic differentiation. Our results indicate that the FTO-mediated m⁶A modification in GADD45B mRNA drives skeletal muscle differentiation by activating the p38 MAPK pathway, which provides a molecular mechanism for the regulation of myogenesis via RNA methylation.