title: Androgen dependent development of a modified anal fin, gonopodium, as a model to understand the mechanism of secondary sexual character expression in vertebrates.
abstract: Male external genitalia show structural variations among species. Androgenic hormones are essential for the morphological specification of male type copulatory organs, while little is known about the developmental mechanisms of such secondary sexual characters. Western mosquitofish Gambusia affinis may offer a clue to the sexual differentiation researches, because they show a prominent masculine sexual character for appendage development, anal fin to gonopodium (GP) transition, and its formation could be induced in early juvenile fry by exogenously supplied androgens. We show that GP development is promoted by androgen dependent augmentation of sonic hedgehog (Shh) expression. Two AR cDNAs were cloned and identified as ARalpha and ARbeta from western mosquitofish. Both ARs were predominantly expressed in the distal region of outgrowing anal fin rays. Exposure of fry to androgen caused anal fin outgrowth concomitant with the Shh induction in the distal anal fin ray epithelium. When AR signaling was inhibited by its antagonist flutamide in fry, the initial induction of the Shh was suppressed accompanying retarded anal fin outgrowth. Similar suppression of anal fin outgrowth was induced by treatment with cyclopamine, an inhibitor of Shh signaling. These observations indicate that androgen dependent Shh expression is required for anal fin outgrowth leading to the formation of a genital appendage, the GP in teleost fishes. Androgen-induced GP formation may provide insights into the expression mechanism regulating the specification of sexual features in vertebrates.
authors.affiliation: Center for Animal Resources and Development (CARD), Graduate School of Medical and Pharmaceutical Sciences, Kumamoto University, Honjo 2-2-1, Kumamoto 860-0811, Japan.
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Ogino
authors.forename: Hironori
authors.initials: H
authors.lastname: Katoh
authors.forename: Gen
authors.initials: G
authors.lastname: Yamada
mesh_terms: D000595:Amino Acid Sequence; D000726:Androgen Antagonists / Q000494:pharmacology; D000728:Androgens / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D003532:Cyprinodontiformes / Q000033:anatomy & histology* / Q000254:growth & development*; D005260:Female; D005485:Flutamide / Q000494:pharmacology; D005837:Genitalia, Male / Q000033:anatomy & histology / Q000187:drug effects / Q000254:growth & development; D053823:Hedgehog Proteins; D017403:In Situ Hybridization; D008297:Male; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011944:Receptors, Androgen / Q000235:genetics / Q000378:metabolism*; D012727:Sex Characteristics; D012733:Sex Differentiation / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D014018:Tissue Distribution; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014704:Veratrum Alkaloids / Q000494:pharmacology
chemical_list: D000726:Androgen Antagonists; D000728:Androgens; D053823:Hedgehog Proteins; D020033:Protein Isoforms; D011944:Receptors, Androgen; D015534:Trans-Activators; D014704:Veratrum Alkaloids; D005485:Flutamide; C000541:cyclopamine