Identification of Wnt4 as the ovary pathway gene and temporal disparity of its expression vis-a-vis testis genes in the garden lizard, Calotes versicolor

Abstract

Sex determination in the Indian garden lizard, Calotes versicolor, which lacks sex chromosomes and temperature-dependent sex determination, appears to be genically controlled, and previous studies have identified orthologues of Sox9, Dmrt1 and Androgen receptor (AR) as genes involved in testis differentiation in genetic males. In the pursuit of female pathway genes in this species, the present paper deals with the identification of Wnt4 and Dax1 genes in C. versicolor and their expression in embryonic gonad. CvDax1 is expressed throughout the development in certain embryos from day 5 onwards but shows no clear association with either testis or ovary. However, its preferred association with CvSox9 in early development and with CvWnt4 during later development suggests a role in the structuring of the gonads. CvWnt4 shows little expression in early development. It expresses prominently from day 20 onwards, and almost exclusively in those embryos that do not express CvSox9, demonstrating that CvWnt4 is the ovary differentiation gene in this species. This evidence leads us to suggest that temporal distinction of expression of ovary-specific (day 20 onwards) and testis-specific (day 5 onwards) genes could be an important part of the process of sex determination in C. versicolor. Taken together, the mechanism of sex determination in C. versicolor appears closer to the CSD in mammals than that in the ESD reptiles and birds.