A single-cell atlas of bovine skeletal muscle tissue reveals mechanisms underlying differences in quality between Wagyu and Brahman beef.

Wagyu cattle are renowned for their premium beef characterized by abundant intramuscular fat (IMF). In contrast, Brahman, a popular breed in the southern coastal area of the US, generally produces tough meat with scarce IMF. However, the mechanisms underlying the differential meat quality between the two breeds are still largely unknown. Using single-cell RNAseq (scRNAseq), we identified many tissue-resident and immune cell types in Wagyu, Brahman, and Wagyu/Brahman crossbred cattle muscle. Multiple fibro/adipogenic progenitor (FAP) subpopulations were identified, including an endomysial adipogenic subpopulation and a perimysial fibrogenic subpopulation. Further analysis comparing individual FAP subpopulations between Wagyu and Brahman identified stronger pro-adipogenic gene expression in Wagyu adipogenic FAP subpopulation and higher pro-fibrogenic gene expression in Brahman fibrogenic FAP subpopulation. Overexpression of CFD, a gene upregulated in Wagyu adipogenic FAPs, enhanced the adipogenic efficiency of FAPs. Moreover, the expression of CFD in FAPs was positively correlated with the IMF content. Interestingly, the expression of CFD was identified in human FAPs but not FAPs of mouse models of intramuscular adipogenesis, suggesting that CFD is a species-specific regulator of IMF formation. Using a mouse line that allows lineage-tracing of FAPs expressing Postn, a gene upregulated in Brahman FAPs, we found that Postn expression was specifically activated during fibrogenic but not adipogenic programming. Cell-cell communication analysis revealed robust interactions between FAPs and other cell types, further suggesting the critical role of FAPs in bovine skeletal muscle growth, development, and homeostasis. To determine the cellular composition of skeletal muscle tissue, we performed scRNAseq using cells isolated from the Longissimus dorsi muscle of 4-month old full-blood Wagyu, purebred Brahman, and Wagyu/Brahman crossbred (50/50; abbreviated as crossbred hereafter) heifer calves. A total of 32,708 cells passed quality control, including 11,765 from Wagyu, 5,903 from Brahman, and 15,040 from crossbred.