Adipose tissue is conventionally recognized as a metabolic organ responsible for storing energy. However, a proportion of adipose tissue also functions as a thermogenic organ, contributing to the inhibition of weight gain and prevention of metabolic diseases. In recent years, there has been significant progress in the study of thermogenic fats, particularly brown adipose tissue (BAT). Despite this progress, the mechanism underlying thermogenesis in beige adipose tissue remains highly controversial. It is widely acknowledged that beige adipose tissue has three additional thermogenic mechanisms in addition to the conventional UCP1-dependent thermogenesis: Ca²⁺ cycling thermogenesis, creatine substrate cycling thermogenesis, and triacylglycerol/fatty acid cycling thermogenesis. This paper delves into these three mechanisms and reviews the latest advancements in the molecular regulation of thermogenesis from the molecular genetic perspective. The objective of this review is to provide readers with a foundation of knowledge regarding the beige fats and a foundation for future research into the mechanisms of this process, which may lead to the development of new strategies for maintaining human health.

MicroRNAs play essential roles in biological processes by regulating gene expression at the post-transcriptional level. Our previous studies suggested the role of miR-26a in porcine fat accumulation. Here, through gain- and loss-of-function analyses, we first showed that miR-26a increased the proliferation of porcine preadipocytes by promoting cell division and that miR-26a inhibited the preadipocyte differentiation. Next, acyl-CoA dehydrogenase, medium chain (ACADM) was revealed to promote the proliferation and differentiation of preadipocytes for the first time. Then, it was revealed that miR-26a regulates adipogenesis by directly binding to the 3′ untranslated region of ACADM and the long-chain acyl-Co A synthetase 1 (ACSL1) gene, a previously known regulator of adipogenesis. Finally, RNA-sequencing, performed on preadipocytes overexpressing miR-26a, identified 337 differentially expressed genes in the early stage of adipogenesis; among them, nine genes were characterized as potential targets of miR-26a. The 337 genes were mainly involved in Gene Ontology terms related to cell division, indicating that cell cycle progression was also a major event regulated by miR-26a during adipogenesis. We provide novel data for understanding the molecular mechanisms underlying adipogenesis, which will contribute to controlling fat accumulation in animals.

Circular RNA (CircRNA) can regulate gene expression through acting as a competitive endogenous RNA (ceRNA), thus becoming involved in various biological processes. However, little was known about the role of circRNA in the formation of meat quality in pigs. Here, circRNAs were first characterized in muscles with differential meat quality and myofiber composition, longissimus thoracis, and semitendinosus muscles, with RNA-sequencing (RNA-seq). A total of 1126 differentially expressed circRNAs were identified. Among them, Circ-06958 is highly expressed in both muscles. Circ-06958 originated from Long-chain acyl-CoA synthetase 1 (ACSL1), a gene involved in muscle development. Circ-06958 was then characterized experimentally for the first time. Next, it was revealed that Circ-06958 increased proliferation of muscle cells, including porcine skeletal muscle satellite cells (PMSCs) and C2C12 myoblasts, by promoting cell cycle progression. Circ-06958 was mainly localized in cytoplasm, indicating it can function as a ceRNA. A regulatory axis Circ-06958/miR-31-5p/Adenylate Kinase 4 (AK4) axis was constructed with molecular biology techniques. Afterward, it was shown that miR-31-5p inhibited cell proliferation by affecting cell cycle progression in the two cells, while AK4 increased it. We made it clear that Circ-06958 promoted muscle cell proliferation via the miR-31-5p/AK4 axis. The results will contribute to further revealing the mechanisms through which meat quality generates.

Alternative splicing (AS) and alternative polyadenylation (APA), as post-transcriptional regulatory mechanisms, are involved in various biological processes through the generation of transcript variants. However, genome-wide studies of AS and APA during spleen development are scarce. This study aimed to characterize transcript diversity and changes in transcript isoforms in the spleen at two developmental stages using full-length isoform sequencing integrated with short-read RNA sequencing. We revealed widespread transcript diversity and identified 17,294 unannotated transcripts, most of which originated from known genes in the current pig genome annotation. The top 500 genes with the highest isoform diversity were mainly associated with disease occurrence and immune function, as revealed by Kyoto Encyclopedia of Genes and Genomes enrichment analysis. We also observed changes in major transcript usage and polyadenylation site selection during spleen development. Our results indicated that genes regulated immunological development mainly by switching dominant transcript isoforms rather than altering overall expression levels. In addition, genes exhibited a tendency of age-dependent preference for distal polyadenylation sites. Furthermore, transcription factors important for spleen development were identified, and the regulatory axes MYBL2/WEE1 and E2F1/WEE1 were constructed for the first time using molecular biology techniques. These findings not only refined the current pig genome annotation, but also provided a foundation for exploring the molecular mechanisms responsible for spleen development.

Meat quality in pigs is fundamentally shaped by the relative abundance and metabolic properties of distinct skeletal muscle fiber types. Dihydrolipoyl dehydrogenase (DLDH), an indispensable catalytic subunit of mitochondrial dehydrogenase complexes, has been documented to link with myocyte development; nevertheless, the effects of the causal regulatory variants governing transcription of its encoding gene DLD on the myogenic fate remain largely uncharacterized. In this study, comparative polymorphism analysis between Large White and Min pigs uncovered a regulatory single nucleotide polymorphism (SNP) at position −143 A>C within the porcine DLD promoter. Mechanistic dissection using dual-luciferase reporter, electrophoretic mobility shift, and chromatin immunoprecipitation assays revealed that the C allele strengthens Krüppel-like factor 2 (KLF2) DNA-binding affinity and potentiates KLF2-mediated transcriptional repression, leading to significantly reduced DLD expression. Functional characterization in porcine primary myoblasts demonstrated that DLD promotes myoblast proliferation by accelerating G2/M transition and upregulating cell-cycle regulators while suppressing terminal differentiation. Furthermore, DLD overexpression inhibited slow-twitch (myosin heavy chain (MYH) 7-positive) myogenic differentiation and suppressed the expression of myogenic regulatory factors MYOD and MYOG, whereas DLD knockdown produced converse effects. Taken together, these multiple lines of evidence suggest that the −143 A>C variant may reinforce transcriptional repression of DLD by increasing KLF2-binding occupancy. Because reduced DLD expression favors MYH7-positive myotube formation in our myoblast assays, this variant is hypothesized to influence myotube subtype balance. These findings may provide a potential molecular mechanism contributing to pork-quality variation and suggest the −143 A>C variant on the DLD promoter as a candidate marker for future genomic-selection studies.

Skeletal muscle, accounting for about 40% of the body’s mass, is an important trait for farm animal production. Skeletal muscle satellite cells (MuSCs) are an excellent material for studying the regulatory mechanisms underlying muscle growth and regeneration after birth. Here, we analyzed the role and underlying mechanisms of Myc-associated zinc finger protein (MAZ) and secretory leukocyte protease inhibitor (SLPI) in porcine MuSC (pMuSC) proliferation for the first time. It was revealed that both MAZ and SLPI advanced the proliferation of pMuSCs by promoting cell cycle progression, and that a MAZ/SLPI axis regulated pMuSC proliferation. It was further shown that this MAZ/SLPI axis regulated pMuSC proliferation through the Wnt/β-catenin pathway. The proliferative role obtained above was confirmed in mouse myoblast C2C12 cells. Additionally, a single-nucleotide polymorphism (SNP), −360C>T, which frequently occurred in the promoter of the SLPI gene from Min, Yorkshire, and Longmin black pigs, was found to significantly increase the gene’s expression in vitro and in vivo. The SNP −360C>T in SLPI is a potential molecular marker predicting the proliferative ability of pMuSCs. The data provide a basis for controlling muscle growth and regeneration, which will provide benefits for improving the meat production of pigs and controlling muscle-related diseases in humans.