Spatiotemporal Expression of Aromatase (CYP19) During Gonadal Sex Differentiation in the Oviparous Lizard Calotes versicolor

Steroidal sex hormones play critical rolest during gonadal sex differentiation and development. Among the sex steroids, estradiol acts at the central level in the sexual differentiation of many reptilian species exhibiting temperature-dependent sex determination (TSD). In recent years, the growing amount of information has highlighted the importance of aromatase (CYP19) in irreversibly catalyzing conversion of androgens into estrogens by aromatization during ovarian morphogenesis. To elucidate the involvement of aromatase in this process we investigated the ontogenic and cellular expression of aromatase in the embryos of the lizard Calotes versicolor that exhibits a unique pattern of TSD. The eggs of this lizard were incubated at 31.5±0.5°C which is 100% Female-Producing Temperature (FPT). The torso of embryos containing Adrenal- Kidney-Gonadal (AKG) complex was collected during different stages of development and subjected to Western blotting and immunohistochemical analysis. Western blot analysis revealed a single immunoreactive protein at 58 kDa for aromatase in the total protein extracts of AKG complex during early Thermo-Sensitive Period (TSP) suggesting early action of aromatase. A very weak but specific immunoexpression of aromatase noticed in the cytoplasm of adrenocortical cells, mesonephric kidney tubules (stage 28) and medullary region of the gonad (stage 30) during early TSP suggests early onset of aromatase activity which in turn indicates that these are the sites of estrogen biosynthesis. Further, a remarkable increase in the intensity of immunoreaction for aromatase during late TSP and gonadal differentiation stage shows it’s up-regulation and estrogen biosynthesis resulting in ovary differentiation. It is inferred that high expression level of aromatase at FPT is associated with proliferation of cortex facilitating differentiation of ovary in C. versicolor .