Single-Nucleus RNA Sequencing Reveals Muscle-Region-Specific Differences in Fibro-Adipogenic Progenitors Driving Intramuscular Fat Accumulation.

Background: Ectopic fat deposition refers to lipid accumulation that affects metabolic function and tissue characteristics. Japanese Black cattle are distinguished by their high intramuscular fat content, which contributes to their distinctive character. However, the genetic mechanisms underlying these traits remain unclear. This study compared gene expression patterns in different muscle regions to identify genes associated with intramuscular fat accumulation. First, we conducted RNA sequencing to analyze differences in gene expression profiles among the sternocleidomastoid, pectoralis minor, and pectoralis major muscles. In addition, single-cell nuclear RNA sequencing was conducted to investigate the cellular composition of these muscle tissues.

Results: Distinct gene expression patterns were observed among the different muscles. In the pectoralis, which contains a high proportion of intramuscular fat, adipocyte-related genes such as , , and were highly expressed. In addition, lipases such as , , , and were predominantly expressed in intramuscular fat, whereas , , and were specifically expressed in myofibers. Moreover, a subclass of fibro-adipogenic progenitor cells that differentiate into intramuscular adipocytes was found to express genes related to microenvironment formation, including , , and members of the family.

Conclusions: This study provides novel insight into the genetic regulation of intramuscular fat accumulation. It improves our understanding of the molecular mechanisms underlying their distinctive meat characteristics.