title: Sexual differentiation of the spinal nucleus of the bulbocavernosus is not mediated solely by androgen receptors in muscle fibers.
abstract: The spinal nucleus of the bulbocavernosus (SNB) neuromuscular system is a highly conserved and well-studied model of sexual differentiation of the vertebrate nervous system. Sexual differentiation of the SNB is currently thought to be mediated by the direct action of perinatal testosterone on androgen receptors (ARs) in the bulbocavernosus/levator ani muscles, with concomitant motoneuron rescue. This model has been proposed based on surgical and pharmacological manipulations of developing rats as well as from evidence that male rats with the testicular feminization mutation (Tfm), which is a loss of function AR mutation, have a feminine SNB phenotype. We examined whether genetically replacing AR in muscle fibers is sufficient to rescue the SNB phenotype of Tfm rats. Transgenic rats in which wild-type (WT) human AR is driven by a human skeletal actin promoter (HSA-AR) were crossed with Tfm rats. Resulting male HSA-AR/Tfm rats express WT AR exclusively in muscle and nonfunctional Tfm AR in other tissues. We then examined motoneuron and muscle morphology of the SNB neuromuscular system of WT and Tfm rats with and without the HSA-AR transgene. We observed feminine levator ani muscle size and SNB motoneuron number and size in Tfm males with or without the HSA-AR transgene. These results indicate that AR expression in skeletal muscle fibers is not sufficient to rescue the male phenotype of the SNB neuromuscular system and further suggest that AR in other cell types plays a critical role in sexual differentiation of this system.
authors.affiliation: Department of Psychology, University of Toronto at Mississauga, 3359 Mississauga Road, Mississauga, Ontario, Canada.
authors.forename: Lee
authors.initials: L
authors.lastname: Niel
authors.forename: Amit H
authors.initials: AH
authors.lastname: Shah
authors.forename: Gareth A
authors.initials: GA
authors.lastname: Lewis
authors.forename: Kaiguo
authors.initials: K
authors.lastname: Mo
authors.forename: Diptendu
authors.initials: D
authors.lastname: Chatterjee
authors.forename: Shannon M
authors.initials: SM
authors.lastname: Fernando
authors.forename: Mei Hua
authors.initials: MH
authors.lastname: Hong
authors.forename: William Y
authors.initials: WY
authors.lastname: Chang
authors.forename: Peter
authors.initials: P
authors.lastname: Vollmayr
authors.forename: Jon
authors.initials: J
authors.lastname: Rosen
authors.forename: Jeffrey N
authors.initials: JN
authors.lastname: Miner
authors.forename: D Ashley
authors.initials: DA
authors.lastname: Monks
mesh_terms: D000818:Animals; D008297:Male; D009046:Motor Neurons / Q000166:cytology; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D055647:Rats, Transgenic; D011944:Receptors, Androgen / Q000235:genetics / Q000502:physiology*; D012733:Sex Differentiation / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology
chemical_list: D011944:Receptors, Androgen