Differential expression of estrogen receptor alpha in the embryonic adrenal–kidney–gonadal complex of the oviparous lizard, Calotes versicolor (Daud.)

• Adrenal–kidney–gonadal (AKG) expression of estrogen receptor studied in embryos of lizard at FPT.
• The ERα antibody recognized two protein bands of ∼55 kDa and ∼45 kDa in the embryonic AKG during TSP.
• Immunohistochemistry revealed AKG expression for ERα initiates during thermo-sensitive period.
• Immunohistochemistry revealed nuclear expression of ERα in medulla of gonad.
• Our study indicates synthesis of estrogen in gonad coincides with sexual differentiation of gonad.

Estrogen signalling is critical for ovarian differentiation in reptiles with temperature-dependent sex determination (TSD). To elucidate the involvement of estrogen in this process, adrenal–kidney–gonadal (AKG) expression of estrogen receptor (ERα) was studied at female-producing temperature (FPT) in the developing embryos of the lizard, Calotes versicolor which exhibits a distinct pattern of TSD. The eggs of this lizard were incubated at 31.5 ± 0.5 °C (100% FPT). The torso of embryos containing adrenal–kidney–gonadal complex (AKG) was collected during different stages of development and subjected to Western blotting and immunohistochemistry analysis.The ERα antibody recognized two protein bands with apparent molecular weight ∼55 and ∼45 kDa in the total protein extracts of embryonic AKG complex of C. versicolor. The observed results suggest the occurrence of isoforms of ERα. The differential expression of two different protein isoforms may reveal their distinct role in cell proliferation during gonadal differentiation. This is the first report to reveal two isoforms of the ERα in a reptile during development.Immunohistochemical studies reveal a weak, but specific, cytoplasmic ERα immunostaining exclusively in the AKG during late thermo-sensitive period suggesting the responsiveness of AKG to estrogens before gonadal differentiation at FPT.Further, cytoplasmic as well as nuclear expression of ERα in the medulla and in oogonia of the cortex (faint activity) at gonadal differentiation stage suggests that the onset of gonadal estrogen activity coincides with sexual differentiation of gonad. Intensity and pattern of the immunoreactions of ERα in the medullary region at FPT suggest endogenous production of estrogen which may act in a paracrine fashion to induce neighboring cells into ovarian differentiation pathway.