Differential distribution and potential regulatory roles of estrogen receptor 2a and 2b in the pituitary of ricefield eel Monopterus albus.

Estrogens play important regulatory roles in the pituitary of vertebrates. Two forms of estrogen receptor 2 (Esr2), namely Esr2a and Esr2b, are identified in teleosts, but their differential roles remain to be fully elucidated. In the present study, expression and potential functional roles of Esr2a and Esr2b were characterized in ricefield eels. esr2a and esr2b mRNA were broadly distributed in tissues, with high levels observed in the brain, pituitary, and gonads. In order to examine the cellular localization of Esr2a and Esr2b in the pituitary, specific antisera against ricefield eel Esr2a and Esr2b were generated, respectively. Interestingly, immunohistochemistry and Western blot analysis revealed that Esr2a and Esr2b were differentially distributed in the pituitary, with the former localized to the adenohypophysis while the latter to the neurohypophysis. Dual fluorescent immunostaining showed that immunoreactive Esr2a was present in Gh and Prl cells, but not in Lh and Fsh cells. Estradiol (E) stimulated lhb and prl gene expression in dispersed pituitary cells of intersexual ricefield eels, but had no effects on gh, fshb, and gnrhr2 gene expression and Gh release. Results of the present study are helpful for further understanding the roles and mechanisms of estrogen signals in the pituitary.