Androgen-Directed Development of the Xenopus laevis Larynx: Control of Androgen Receptor Expression and Tissue Differentiation

Abstract

The larynx of adult male Xenopus laevis differs markedly from that of the female; masculinization of the larynx requires androgen secretion during postmetamorphic development. Early in postmetamorphic development, androgen stimulates laryngeal cell proliferation and androgen binding activity is high. Later, androgen induces laryngeal cell differentiation and binding levels decrease. Here we explore the relation between laryngeal differentiation and androgen receptor expression. In untreated females, the larynx expresses high levels of androgen receptor mRNA early in postmetamorphic life; levels decline as females mature. The highest level of androgen receptor message is found in the undifferentiated laryngeal elastic precartilage of both sexes. When juveniles are exposed to androgen, laryngeal cell proliferation is stimulated within 48 hr in both sexes. Short exposures to androgen result in a biphasic response of AR mRNA levels; a marked down-regulation (4 hr) is followed by recovery at 8 hr (males) or 48 hr (females). Following longer periods of androgen treatment (3 weeks), AR mRNA expression is down-regulated and male-typical differentiation of elastic cartilage is induced in both sexes. Thus laryngeal growth responses to androgen are closely related to expression levels of androgen receptor mRNA.

Testosterone Regulates Androgen Receptor Immunoreactivity in the Copulatory, but not Courtship, Neuromuscular System in Adult Male Green Anoles

“…AR is commonly expressed in vertebrate muscle fibres, particularly in muscles that are sexually dimorphic (36, 41–43). The present data demonstrate that testosterone treatment increases AR expression in lizard muscle fibres that exhibit morphological sensitivity to testosterone.…”

“…In male Xenopus, widespread AR immunoreactivity is detected in skeletal muscle fibres, including those that do not change in size in response to testosterone manipulation (41). Furthermore, in the sexually dimorphic and androgen sensitive larynx, 3 weeks of androgen treatment in adulthood causes a decrease in AR mRNA expression (42), although expression of AR protein and mRNA are not always complementary (32). Finally, although testosterone does increase AR immunoreactivity in rat muscles that exhibit morphological responsiveness to androgens, it also does so in those that do not (36).…”

Sexual differentiation and hormonal regulation of the laryngeal synapse in Xenopus laevis

“…I to 0. I5 mg/g body weight) (Fischer et al, 1995) were prepared. The Silastic capsule was placed into the dorsal lymph sac via a small incision just caudal to the orbit.…”

Androgen-Induced Vocal Transformation in Adult Female African Clawed Frogs

“…Surprisingly, rapid vocal transformation was observed. We next examined the rates at which the laryngeal muscles and the laryngeal motoneurons transformed in response to T. Both laryngeal muscle fibers and laryngeal motoneurons of male and female Xenopus express androgen receptors (Fischer et al 1995;Kelley 1980;Kelley et al 1975) and therefore may be masculinized at independent rates. Examination of vocal behavior, muscle physiology, and motoneuron size in parallel led us to conclude that the T-induced transformation of vocal behavior reflects the rate at which the central vocal pathways functionally transform to generate rapid motor rhythms; peripheral elements seem to be modified much more quickly.…”