Explore the vast range of titles available.

The structural and functional characteristics of skeletal muscle fibers play a crucial role in understanding the physical capabilities of dogs, particularly in relation to their breed-specific roles. This study aimed to compare the muscle fiber composition of working and companion dog breeds by analyzing the triceps brachii and biceps femoris muscles, focusing on fiber morphology, myosin heavy chain (MYH) isoform distribution, and nuclei per fiber. A total of 12 dogs, divided equally into working and companion breed groups, were used in this study. Muscle samples were collected post-mortem and prepared for histological analysis using cryosectioning. Immunohistochemical staining was employed to identify the expression of MYH isoforms, including MYH2, MYH4, and MYH7, which correspond to type IIa, IIb, and type I fibers, respectively. The results demonstrated significant differences between the two breed groups. Working dogs exhibited larger muscle fibers, a higher proportion of type IIa (MYH2) and type I (MYH7) fibers, and a greater number of nuclei per fiber, suggesting adaptations for endurance and strength. In contrast, companion dogs showed a higher proportion of type IIb (MYH4) fibers, indicative of their capacity for short bursts of activity rather than sustained exertion. Companion breeds also displayed a higher fiber density but fewer nuclei per fiber, which may contribute to slower muscle regeneration. These findings may provide insights into the muscle adaptations of dogs based on their breed-specific functional demands and highlight the importance of considering these differences in veterinary care and rehabilitation. The study underscores the influence of selective breeding on muscle structure and function in dogs and suggests further research into breed-specific muscle recovery mechanisms.

Background Small mammals such as mice rely on type IIb myofibers, which express the fast-contracting myosin heavy chain isoform Myh4 , to achieve rapid movements. In contrast, larger mammals, including humans, have lost MYH4 expression. Thus, they favor slower-contracting myofiber types. However, the mechanisms underlying this evolutionary shift remain unclear. We recently identified the large Maf transcription factor family ( Mafa , Mafb , and Maf ) as key regulators of type IIb myofiber specification in mice. In this study, we investigate whether large MAFs play a conserved role in the induction of MYH4 expression and glycolytic metabolism in human and bovine skeletal muscle. Methods We performed adenovirus-mediated overexpression of large MAFs in iPSC-derived human myotubes and primary bovine myotubes. We subsequently quantified MYH4 expression using RT-qPCR, RNA sequencing (RNA-seq), and LC-MS/MS analysis. Glycolytic capacity was assessed using a flux analyzer and metabolic gene expression profiling. Additionally, RNA-seq analysis of human muscle biopsy samples was conducted to determine the correlations between large MAFs and the expression of MYH4 and other myosin genes, as well as their association with fast fiber composition and athletic training. Results Overexpression of large MAFs in human and bovine myotubes robustly induced MYH4 expression, with mRNA levels increasing by 100- to 1000-fold. LC-MS/MS analysis provided clear evidence of MYH4 protein expression in human myotubes, where it was previously undetectable. RNA-seq and flux analyzer data revealed that large MAFs significantly enhanced glycolytic capacity by upregulating the expression of key genes involved in glucose metabolism. Moreover, RNA-seq analysis of human muscle biopsy samples revealed a positive correlation between MAFA , MAF , and MYH4 expression. Furthermore, MAFA and MAF expression levels were elevated in power-trained individuals, accompanied by increased expression of MYH4 and other fast myosin genes. Conclusions Our findings establish large MAF transcription factors as key regulators of MYH4 expression and glycolytic metabolism in human skeletal muscle. This discovery provides novel insights into the evolutionary loss of type IIb myofibers in larger mammals and suggests potential strategies for enhancing muscle performance and mitigating fast-twitch fiber loss associated with aging and muscle degeneration.

The nuclear pore complex (NPC) has emerged as a hub for the transcriptional regulation of a subset of genes, and this type of regulation plays an important role during differentiation. Nucleoporin TPR forms the nuclear basket of the NPC and is crucial for the enrichment of open chromatin around NPCs. TPR has been implicated in the regulation of transcription; however, the role of TPR in gene expression and cell differentiation has not been described. Here we show that depletion of TPR results in an aberrant morphology of murine proliferating C2C12 myoblasts (MBs) and differentiated C2C12 myotubes (MTs). The ChIP-Seq data revealed that TPR binds to genes linked to muscle formation and function, such as myosin heavy chain (Myh4), myocyte enhancer factor 2C (Mef2C) and a majority of olfactory receptor (Olfr) genes. We further show that TPR, possibly via lysine-specific demethylase 1 (LSD1), promotes the expression of Myh4 and Olfr376, but not Mef2C. This provides a novel insight into the mechanism of myogenesis; however, more evidence is needed to fully elucidate the mechanism by which TPR affects specific myogenic genes.