Skeletal muscles that actuate sexual displays are specialized forde novoandrogen synthesis

Abstract

1The gonads (testes) act as the primary organ where androgenic hormones are 2 made to regulate reproductive behavior in male vertebrates. Yet many endocrinologists 3 have also long suspected that other tissues in the body can autonomously synthesize their 4 own androgens to support behavioral output. We examine this idea here by studying 5 whether avian skeletal muscles that actuate elaborate socio-sexual displays are 6 specialized to maintain the molecular machinery otherwise needed for de novo androgen 7 synthesis. Our results show that the vocal organ, or syrinx (SYR), of two songbirds 8 species does in fact express all transporters and enzymes necessary to create androgenic 9 hormones from scratch. This includes genes that encode proteins to mediate rate-limiting 1 0 steps of steroidogenesis, which are seldom found outside of the gonads. We also show 1 1 that expression levels of these genes are far greater in the SYR than non-display muscles,