Sittipon Intarapat; Achariya Sailasuta & Orawan Satayalai

In birds, male embryo the gonads develop bilateral testes, in which both left and right sides produce functional spermatozoa, whereas female embryo, only the left gonad develops into a functional ovary. Estrogen plays a key role in avian sex determination in both sexes by binding to the estrogen receptor (ER). Surprisingly, chicken estrogen receptor (cER) mRNA is expressed in both sexes; moreover; its expression is only expressed in the left male gonad. The present study aimed to localize ER protein in the left gonad of male quail embryo using immunohistochemistry. The 8-day-old male quail embryos whose embryonic sex distinguished by gonadal morphology were studied. Histology of the left male gonad displayed thin cortex containing 1 to 2 layers of the germinal epithelium, while testicular cords were observed in the medulla. ER-immunoreactive cells were only found in the germinal epithelium but not in the medulla. Localization of ER was detected in the nucleus and cytoplasm of the germinal epithelial cells. The number of ER-immunoreactive cells counted in upper, lateral, and lower regions of the germinal epithelium was 18.20±1.892, 17.60±1.887, and 16.20±1.290, respectively. This study shows the first evidence for expression of ER protein in the left male gonad of the avian embryo, indicating that ER plays a role in avian gonadal sex differentiation.

KEY WORDS: Estrogen receptor; Embryonic gonad; Gonadal differentiation; Quail embryo.

INTARAPAT, S.; SAILASUTA, A. & SATAYALAI, O. Immunohistochemical localization of estrogen receptor in the embryonic gonad of male quail embryo during gonadal differentiation. Int. J. Morphol., 34(2):575-579, 2016.