Sexually dimorphic expression of a laryngeal-specific, androgen-regulated myosin heavy chain gene during Xenopus laevis development

Abstract

Masculinization of the larynx in Xenopus laevis frogs is essential for the performance of male courtship song. During postmetamorphic (PM) development, the initially female-like phenotype of laryngeal muscle (slow and fast twitch fibers) is converted to the masculine form (entirely fast twitch) under the influence of androgenic steroids. To explore the molecular basis of androgendirected masculinization, we have isolated cDNA clones encoding portions of a new Xenopus myosin heavy chain (MHC) gene. We have detected expression of this gene only in laryngeal muscle and specifically in males. All adult male laryngeal muscle fibers express the laryngeal myosin (LM). Adult female laryngeal muscle expresses LM only in some fibers. Expression of LM during PM development was examined using Northern blots and in situ hybridization. Males express higher levels of LM than females throughout PM development and attain adult levels by PM3. In females, LM expression peaks transiently at PM2. Treatment of juvenile female frogs with the androgen dihydrotestosterone masculinizes LM expression. Thus, LM appears to be a male-specific, testosterone-regulated MHC isoform in Xenopus laevis. The LM gene will permit analysis of androgen-directed sexual differentiation in this highly sexually dimorphic tissue.

Sexually differentiated, androgen-regulated, larynx-specific myosin heavy-chain isoforms in Xenopus tropicalis; comparison to Xenopus laevis

“…MyHC 101d expression is thus responsible for the contractile properties and fiber type composition of the male laryngeal muscle, while the female muscle reflects the contribution of several isoforms. Sex differences in myosin isoform expression in X. tropicalis larynx resemble those seen in X. laevis, with the male muscle being larger (Sassoon and Kelley 1986), having a homogenous fiber type (Sassoon et al 1987) and expressing a male-specific MyHC isoform (Catz et al 1992).…”

“…In X. laevis, the male laryngeal muscle expresses an androgen-regulated MyHC isoform that is specific to the larynx (Catz et al 1992). To determine whether this is also the case for X. tropicalis, we used restriction fragment analysis to identify which MyHC gene products are expressed in male and female laryngeal muscles.…”

“…Laryngeal muscles of the African clawed frog, Xenopus laevis, are sexually dimorphic in fiber type composition (Sassoon et al 1987), contractile properties (Tobias and Kelley 1987), and MyHC gene expression (Catz et al 1992). These muscles express a laryngeal-specific MyHC isoform (laryngeal myosin or xlMyHC-LM) at much higher levels in males than in females or juveniles (Catz et al 1992).…”

“…These muscles express a laryngeal-specific MyHC isoform (laryngeal myosin or xlMyHC-LM) at much higher levels in males than in females or juveniles (Catz et al 1992). The entirely fast-twitch composition of male laryngeal muscle (Sassoon et al, 1987) supports the rapid (>70 Hz) production of tension transients that produce click sounds (Kelley 2002).…”

Adaptations for rapid and forceful contraction in wing muscles of the male golden-collared manakin: sex and species comparisons

“…Sex steroid hormones have been shown to regulate myosin expression in the mouse masseter, Xenopus larynx, and guinea pig temporalis (Lyons et al 1986;Morano 1991;Eason et al 2000). Seasonal changes in circulating sex steroids may also regulate myosin isoform expression in the manakin SH and SC, including unique muscle speci®c isoforms as identi®ed in the larynx of Xenopus (Catz et al 1992).…”