Prolactin opens the sensitive period for androgen regulation of a larynx-specific myosin heavy chain gene

The larynx of Xenopus laevis is a sexually differentiated vocal organ in wh ich male muscle is entirely fast twitch and expresses high levels of a fast twitch myosin heavy chain gene, LM. Female muscle, however, is mostly slow twitch and expresses little LM. Androgen is unable to induce expression of LM until after metamorphosis is complete. The expression of LM during meta morphic and early postmetamorphic development parallels secretion and expre ssion of the pituitary hormone prolactin, Here, we show that exposure to pr olactin is neccessary to allow androgen-induced LM expression in postmetamo rphic froglets, In prolactin-deprived animals, androgen-induced changes in the contactile properties of laryngeal muscle are blocked, which prevents t he rapid rates of muscle contraction required for males to produce courtshi p songs. Thus, prolactin opens the sensitive period for androgen-induced LM expression in the larynx and controls the ability of male sex hormones to masculinize the vocal system both at the level of gene expression and vocal organ physiology. (C) 1999 John Wiley & Sons, Inc. J Neurobiol.