Abstract
The transmembrane protein FNDC5 was recently characterized as precursor of an exercise induced myokine named irisin. Previous studies found a relationship between circulating irisin levels and muscle mass in humans. Consequently, we tested the hypothesis whether FNDC5/irisin is involved in the modulation of body composition in cattle. Since information on the bovine FNDC5 locus was scarce, we characterized the gene experimentally as prerequisite for these investigations. We provide here a revised and extended gene model for bovine FNDC5. Although similarly organized like the human and murine loci, a higher variability was observed at transcript level in the bovine locus. FNDC5 mRNA was abundant in bovine skeletal muscle and was detected at lower levels in adipose tissue and liver. There were no expression differences between two groups of bulls highly different in muscularity and adiposity. Full-length FNDC5 protein (25 kDa) was present in bovine skeletal muscle independent of muscularity. Neither FNDC5 nor its putatively secreted peptide irisin were found in circulation of bulls. In contrast, we demonstrated that FNDC5 (25 kDa) and irisin (12 kDa) were present in murine skeletal muscle and that irisin was circulating in murine serum. This indicates fundamental differences in the regulation of FNDC5 and irisin between rodents and cattle.
Highlights
Fibronectin type III domain containing 5 (Fndc5) was originally described as crucial factor for cellular differentiation of skeletal muscle in embryonic mice
Samples were collected from M. longissimus dorsi (LM), M. semitendinosus (SM), subcutaneous adipose tissue (SAT) and liver immediately after slaughter and stored in liquid nitrogen until further processing
A Revised Gene Model for the Bovine FNDC5 Locus The bovine gene for FNDC5 was automatically annotated on chromosome (BTA) 2 (GenBank accession number GK000002.2) and comprises two exons
Summary
Fibronectin type III domain containing 5 (Fndc5) was originally described as crucial factor for cellular differentiation of skeletal muscle in embryonic mice. It was predominantly detected in peroxisomes [1]. Strong expression in murine, embryonic brain but a weak signal in murine skeletal muscle was observed in another study [2]. It was not until a decade later that Fndc attracted attention again, when Bostrom et al [3] characterized it as precursor of a protein named irisin. Irisin was increased after physical activity and suggested to mediate - at least in part - beneficial effects of exercise on metabolism [3]
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