Temporal constraints on androgen directed laryngeal masculinization in Xenopus laevis

Abstract

Temporal constraints on androgen regulated masculinization of three sexually dimorphic laryngeal properties-tension, fiber type, and fiber recruitment-were examined in Xenopus laevis frogs.Endocrine state was manipulated at PM0 when the larynx is similar in males and females, at PM2 when the larynx begins sexual differentiation, and at PM6 when sexual differentiation is complete. Removing the testes in developing males (PM0 or PM2) completely arrests laryngeal masculinization. Masculinization resumes when testosterone is replaced later in development (PM2 or PM6, respectively). Thus, testicular secretions, in particular androgens, are required for laryngeal masculinization. The ability of androgens to masculinize tension, fiber type, and fiber recruitment in developing and adult larynges was also determined. Five weeks of testosterone treatment in PM0 or PM2 males and females completely masculinizes laryngeal tension and fiber type, but only partially masculinizes fiber recruitment. However, fiber recruitment can be fully masculinized in PM6 males castrated at PM2. We conclude that androgen induced masculinization of tension and fiber type are not temporally constrained but that androgen induced masculinization of fiber recruitment is. Prolonged androgen treatment can override the temporal constraints on masculinization of the larynx. Testosterone treatment for more than 6 months fully masculinizes fiber recruitment in developing (PM0 or PM2) females. In addition, prolonged treatment (>9 months) completely masculinizes tension, fiber type, and fiber recruitment in adult females; these properties were not fully masculinized by shorter (1-3 months) treatments in adult females. Testosterone induced masculinization in females is maintained for up to 8 months following testosterone removal; thus androgen effects are long lasting and possibly permanent.

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

“…This androgen sensitivity is very similar to that of X. laevis, where androgen treatment brings about an increase in the size of the larynx and the size of muscle fibers and results in all muscle fibers having acid-sensitive ATPase activity (Tobias et al 1993) as well as the expression of xlMyhC-LM (Catz et al 1995). In X. laevis, endogenous androgen appears responsible for male-specific laryngeal traits because castration halts masculinization (Tobias et al 1991b;Catz et al 1995). Both X. laevis and X. tropicalis, therefore, appear to exhibit a conserved androgen-sensitive process of masculine development leading to a change in muscle fiber properties and in MyHC isoform expression.…”

“…The ability to produce these rapid contractions develops during the first 6 months of postmetamorphic development (Tobias et al 1991a). Masculinization is halted by castration (Tobias et al 1991b), and greatly accelerated by the administration of exogenous androgens to juveniles (Tobias et al 1993). …”

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

“…7D); hypertrophy is also apparent in DHT-treated PM2 female laryngeal muscle (Fig. 7C) and has been reported previously in response to androgen at this stage (Sassoon and Kelley, 1986;Sassoon et al, 1987;Tobias et al, 1991b).…”

“…Administration of androgen to juvenile male or female frogs rapidly switches the heterogeneous population of muscle fibers to all fast twitch. Castration blocks fiber type conversion in juvenile males (Sassoon et al, 1987;Tobias et al, 1991b). We thus examine whether expression of the sexually differentiated MHC identified here is affected by androgen and whether its expression follows the same temporal pattern as fiber type conversion.…”

“…Postmetamorphic stage was determined as described previously (Tobias et al, 1991a). In a separate experiment, PM2 females and males were implanted with dihydrotestosterone propionate (DHT, Sigma) pellets (0.5 mg/g body weight) for 3 weeks (procedure in Tobias et al, 1991b) and then were sacrificed.…”