Genetic and functional validation of <scp><i>CTSS</i></scp> in regulating intramuscular fat content of Duroc–Landrace–Yorkshire pigs

Intramuscular fat (IMF) is an important meat quality trait and a key target for molecular breeding in pigs. Our previous genome-wide association study identified SNP rs80931414 (A>G) as a significant site associated with IMF content. In this study, we further performed genotyping and association analysis of SNP rs80931414 within a Duroc-Landrace-Yorkshire (DLY) pig population. We found that the IMF content in pigs with AA genotype was significantly higher than that in those with GG genotype. SNP rs80931414 is a genetic variation in CTSS, therefore we hypothesized that CTSS is a candidate gene for IMF content trait in DLY pig and conducted research on gene function of CTSS. Our results indicated that both the mRNA and protein expression levels of CTSS were associated with the expressions of adipogenesis-related genes in skeletal muscle. Overexpression of CTSS promoted adipogenesis in intramuscular preadipocytes, while interference with CTSS inhibited this process. Our findings showed that SNP rs80931414 (A>G), which is a genetic variation in CTSS is related to IMF content and CTSS is a candidate gene for IMF content trait in DLY pig. This study provides the first evidence of the role of CTSS in pig intramuscular preadipocytes and offers insights for the development of breeding strategies aimed at genetically improving IMF content in pork.