• B6.YTir;
  • gene expression;
  • ovary;
  • sex differentiation;
  • sex reversal;
  • testis


B6.YTir (mice with Y chromosome from a strain in Tirano, Italy, and autosomes and X-chromosomes from the B6 strain) mice provide an excellent model for analysing sex development that occurs during gonadal differentiation; however, the molecular mechanisms that contribute to sex reversal are unclear. Our aim has been to establish which molecular events participate in this sex reversal. The pattern of gene expression related to testicular [Sry (sex-determining region of the Y chromosome), Sox9 (Sry-related high-mobility group box gene 9) and Mis (Müllerian-inhibiting substance)] and ovarian [Wnt4 (Wingless-type MMTV (murine-mammary-tumour virus) integration site family, member 4), Rspo1 (cysteine-rich secretory protein containing a thrombospondin type 1 repeat) and Stra8 (stimulated by retinoic acid gene 8)] differentiation was analysed by applying immunofluorescence and real-time RT—PCR (reverse transcription—PCR), focusing on XY gonads from the B6.YTir mouse, but also analysing the normal strains CD-1 and C57BL/6J (B6). The expression of genes related to the process of sexual differentiation was altered in the case of the B6.YTir strain, both at the transcript and protein level, inducing differentiation of ovaries and ovotestes, but not the formation of the testes, which were normal. Our results indicate that the expression of testicular genes is inhibited at various levels, permitting the expression of ovarian genes such as Wnt4, Stra8 and Rspo1. However, their activity was not clear when the data were averaged. Correlation analysis indicated that an ovary differentiation pathway is activated when the testicular differentiation pathway is inhibited.