title: Effects of methyl testosterone exposure on sexual differentiation in medaka, Oryzias latipes.
abstract: Studies were conducted to characterize effects of a known androgen on sexual differentiation and development of medaka, Oryzias latipes (d-rR strain), at two life stages. Embryos were injected with graded doses of methyl testosterone (MT) prior to epiboly. The occurrence of sex-reversal, and the gonadosomatic index (GSI) were evaluated in adults. Primary germ cells were counted and gonad volumes calculated for larvae to determine if sex-reversal could be detected at an early life stage. Sex-reversal of genetic females to phenotypic males was observed at both life stages. The GSI for phenotypic females was greater than for phenotypic males, while the GSI in XX males was similar to XY males. MT appeared to reduce the GSI of XX females exposed to MT but not sex-reversed. Our results indicate that embryonic exposure to androgens influences sexual development in medaka. Utilizing the d-rR strain of medaka allows detection of an effect as early as 2 weeks after chemical exposure making this a useful tool to screen chemicals for effects on sexual differentiation.
authors.affiliation: Columbia Environmental Research Center, US Geological Survey, 4200 New Haven Road, Columbia, MO 65201, USA. diana_papoulias@usgs.gov
authors.forename: D M
authors.initials: DM
authors.lastname: Papoulias
authors.forename: D B
authors.initials: DB
authors.lastname: Noltie
authors.forename: D E
authors.initials: DE
authors.lastname: Tillitt
mesh_terms: D000818:Animals; D005260:Female; D057850:Hermaphroditic Organisms; D007814:Larva / Q000187:drug effects; D008297:Male; D008777:Methyltestosterone / Q000633:toxicity*; D009990:Oryzias / Q000196:embryology*; D010641:Phenotype; D019849:Sex Determination Processes; D012733:Sex Differentiation / Q000187:drug effects*; D013997:Time Factors
chemical_list: D008777:Methyltestosterone