Molecualr and Developmental Studies on Genetic Control for Sexual Differentiation in Birds

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We investigated the following subjects in order to elucidate genetic factors that control sexual differentiation in birds ; 1) research for genes related to sexual differentiation on sex chromosome, 2) gene expression of sex steroid hormones and metabolic enzymes, 3) mechanism of alternative development of female gonads.1) We did not get satisfactory results about searching genes on sex chromosome in this research period, because no DNA bands were detected in chickens and quails by hydridization analysis with probes of the Sry gene in mice and W chromosome specific DNA in chickens, respectively. 2) The onsent and localization of P450 aromatase (P450arom) mRNA expression were studied in the gonad of chickens. Levels of P450arom mRNA in the left ovary were invariably higher than those of the right ovary and testis throughout the period between day 10 incubation and 7 days of posthatching. In situ hybridization analysis showed the first detection of P450arom at day 6.5 of incubation in the female gonad. These results suggest that expression of P450arom mRNA occurring in the genetic female gonad around day 6 is associated with sexual differentiation toward femaleness by increasing estrogen production which may promote cellular proliferation of the left gonad. 3) In the study on gonadal differentiation we used the double-oviduct line of the chicken. This line develops and retains the right oviduct throughout its life while it is degenerated before hatching in normal chickens. We observed the right oviduct of this line in order of age and found the variation of developmental degree of the right oviduct within the line. The pair-mating experiment suggests that genetic effect of sire (whose phenotype concerned with the double-oviduct is not detectable) is sufficiently high. We intend to proceed with the genetical analysis of the double-oviduct gene and examine the mechanism of development/degeneration of the right gonad.