In our previous a study, circ_003628 was one of the most highly expressed circular RNAs (circRNAs) in the Longissimus dorsi muscle of goats found by RNA-seq, suggesting that the circRNA may be important for caprine muscle growth and development. However, there have been no reports describing the molecular mechanisms by which circ_003628 regulates the activities of goat skeletal muscle satellite cells (SMSCs). In this study, reverse transcriptase-PCR (RT-PCR) and DNA sequencing were used to validate the authenticity of circ_003628, and its characteristics, expression profile and effect on goat SMSCs were also studied using real-time quantitative-PCR (RT-qPCR), EdU, CCK-8 and immunofluorescence assays. Circ_003628 is partially originated from 13 exons, 12 introns and 3′-untranslated regions (UTR) of caprine Myosin Heavy Chain 1 (MYH1), and 25 exons and 5′ UTR of Myosin Heavy Chain 4 (MYH4), as well as intergenic sequences between the two genes. A total of 77.07% of circ_003628 were located in the nuclei of goat SMSCs, while 22.93% were expressed in the cytoplasm. The circRNAs were only expressed in triceps brachii, quadriceps femoris and longissimus dorsi muscle tissues in nine caprine tissues investigated, with the highest expression level in longissimus dorsi muscle. The expression level of circ_003628 gradually increased during differentiation periods of goat SMSCs and reached the maximum on day 6 after differentiation. The small interfering RNA of circ_003628 (named si-circ_003628) inhibited the viability and proliferation of goat SMSCs, and also decreased the expression of four cell proliferation marker genes: paired box 7 (Pax7), cyclin-dependent kinase 2 (CDK2), CDK4 and CyclinD1 in goat SMSCs. Transfection of si-circ_003628 significantly decreased the area of MyHC-labeled myotubes of goat SMSCs, as well as the expression levels of three differentiation marker genes: myosin heavy chain (MyHC), myogenin (MyoG), and myocyte enhancer factor 2C (MEF2C). These results suggest that circ_003628 promotes the viability, proliferation, and differentiation of goat SMSCs, and they also provide an improved understanding of the roles of circ_003628 in skeletal muscle growth and development in goats.

Keratin (K) is a major protein component of hair and is involved in hair growth and development. In this study, we analysed the expression, localization, and polymorphism of the K84 gene (KRT84) in Gansu Alpine Fine-wool sheep using immunofluorescence, RT-qPCR, and PARMS (penta-primer amplification refractory mutation system). Haplotypes of KRT84 were also constructed and their relationship with wool traits analysed. It was revealed that KRT84 was highly expressed in hair follicles, including the inner root sheath, outer root sheath, and hair medulla and at all six lamb ages investigated from 1 to 270 days of age. Three SNPs were detected in KRT84 exon 1, and they formed three haplotypes (named H1, H2, and H3) and six genotypes. Analyses revealed an association between haplotype combinations (diplotypes) and the mean fibre curvature, mean staple length, mean staple strength, mean fibre diameter, the coefficient of variation of fibre diameter, and comfort factor for these sheep. These results suggest that KRT84 is of importance in determining several key traits in Gansu Alpine Fine-wool sheep and that the gene could possibly be used as a genetic marker for wool trait selection in these sheep.

Oleic acid is a major monounsaturated fatty acid, which accounts for about 33% of the fatty acid content in beef and is considered to have the least negative effect on serum cholesterol levels. Fatty acid transport protein 1 (FATP1), an integral membrane protein that facilitates long-chain fatty acid (LCFA) influx, is involved in the genetic network for oleic acid synthesis in beef. Its expression exhibits significant positive correlations with intramuscular fat (IMF) content in the longissimus thoracis. However, the expression mechanism of SLC27A1 or FATP1 is still unclear. To elucidate the molecular mechanisms involved in bovine SLC27A1 regulation, we cloned and characterized the promoter region of SLC27A1. By applying 5′-rapid amplification of cDNA end analysis, we identified two alternative splice variants of this gene. Using a series of 5′ deletion promoter plasmids in luciferase reporter assays, we found that the core promoter was 96 base pairs upstream from the transcription initiation site. Electrophoretic mobility shift assay combined with a site-directed mutation experiment demonstrated that KLF15 binding to the promoter region drives the SLC27A1 transcription. KLF15 plays an essential role in adipogenesis and skeletal muscle lipid flux. Thus, these results might provide further information on the regulatory roles of SLC27A1 gene in mediating the lipid composition in beef.

Tibetan sheep are an important livestock breed adapted to the extreme environment of the Qinghai–Tibet Plateau (QTP). Their energy metabolism and environmental adaptability are highly dependent on the rumen microbiome. However, systematic comparisons of the rumen microbiome, its functions, and the resistome between plateau-adapted breeds and lowland breeds remain insufficient. In this study, 6 Tibetan sheep (TS) and 6 Hu sheep (HS) were selected. All the selected sheep had a body weight of 34 kg (±0.5 kg) and an age of 1 year (±1 month) and were all managed under local traditional natural grazing (without supplementary feeding). Using metagenomics and metabolomics techniques, systematic comparative analysis was conducted on the differences in rumen microbial community structure, functions, resistome, and metabolites between the two breeds. Metagenomic analysis showed that at the phylum level, the abundance of Bacteroidetes in the rumen of TS was significantly higher than that in HS (p < 0.05); at the genus level, the abundance of Bacteroides in TS was also significantly higher (p < 0.05). Carbohydrate-active enzymes (CAZy) analysis indicated that the abundance of Glycosyltransferases (GTs) and Carbohydrate-Binding Modules (CBMs) in the rumen of TS were significantly upregulated (p < 0.05), while HS was rich in various Glycoside Hydrolases (GHs). Comprehensive Antibiotic Resistance Database (CARD) analysis revealed that more than 60% of the Antibiotic Resistance Genes (ARGs) in the rumen of HS were present at higher levels than those in TS. Metabolomics identified a large number of differential metabolites, among which metabolites such as 2E,6Z,8Z,12E-hexadecatetraenoic acid, Leukotriene F4, and Tenurin were significantly upregulated in the rumen of TS. Correlation analysis showed that rumen microbial flora and their metabolites jointly act to regulate rumen ARGs. Specifically, microorganisms including Firmicutes and Succiniclasticum had a significantly positive correlation with ARGs such as rpoB2 (p < 0.05), while differential metabolites like endomorphin-1 and Purothionin AII exhibited a significantly negative correlation with ARGs such as rpoB2 (p < 0.05). Therefore, compared with HS, the synergistic effect of the rumen microbial flora, their metabolites, and the resistome in TS is an important characteristic and strategy for their adaptation to the hypoxic environment of the QTP, and also contributes to the formation of their unique rumen resistome. Despite being reared in the same plateau environment, the rumen microbiome of HS still retains low-altitude characteristics, which are manifested as high GHs activity and high ARGs abundance.