Agouti Signaling Protein and Its Receptors as Potential Molecular Markers for Intramuscular and Body Fat Deposition in Cattle.

Transcriptome analyses of bovine muscle tissue differing in intramuscular fat (IMF) content identified agouti signaling protein (ASIP) as a promising candidate gene for fat deposition. The protein is secreted from adipocytes and may serve as a signaling molecule in cross-talk between adipocytes and muscle fibers or other cells. Known receptors for ASIP are the melanocortin receptors (e.g., MC4R) and attractin (ATRN). The present study was conducted to determine relationships between the expression of and its receptors in different bovine tissues with fat deposition. Adipose tissues, liver, and longissimus muscle tissue were collected from 246 F-generation bulls (Charolais × Holstein cross) and gene expression was measured with RT-qPCR. During analysis of subcutaneous fat (SCF) of all bulls, 17 animals were identified with a transposon-derived transcript (Exon2C) inserted in the gene and dramatically increased mRNA levels. Significant correlations between normalized mRNA values of SCF and phenotypic traits related to fat deposition were found in bulls without Exon2C. Three retrospectively assigned groups [Exon2C, = 17; high carcass fat (HCF), = 20; low carcass fat (LCF), = 20] were further analyzed to verify expression differences and elucidate molecular reasons. Expression of could be detected in isolated muscle fibers and adipocytes of Exon2C bulls in contrast to HCF and LCF bulls, indicating ectopic expression if the transposon is present. Among adipose tissues, highest mRNA levels were measured in SCF with significantly higher values in HCF compared to LCF bulls (1.6-fold, < 0.05). However, the protein abundance was below the detection limit in all bulls. Potential ASIP receptors were detected in most investigated tissues. The expression of was higher and of was lower in several tissues of LCF compared to HCF bulls, whereas was not differentially expressed. Bulls of the Exon2C group had lower mRNA values than HCF and LCF bulls in perirenal fat (PF), but higher ( < 0.05) values in muscle. Receptors were also expressed in tissues where mRNA was not detected. Consequently, those tissues could be targets for ASIP if it circulates.