Changes in estrogen receptor alpha expression in the bursa of fabricius during chick embryonic development

Sex steroid hormones have been reported to be modulators that augment or suppress immune functions. Applying estrogen to chick embryos has been reported to influence antibody production after hatching, suggesting that estrogen acts on B cell differentiation and proliferation in the bursa of chick embryos. We previously reported the presence of estrogen receptor alpha (ERalpha) in the bursa during the late period of embryogenesis. In the present study we examined the time course of ERalpha expression in the bursa of chick embryos at the late period of embryogenesis by ERalpha-messenger RNA (mRNA) expression analysis by reverse-transcription-polymerase chain reaction (RT-PCR) using primers for chicken ERalpha, and immunohistochemistry using an anti-ER antibody. The quantity of ERalpha-mRNA expressed, estimated from the relative densities of the ERalpha RT-PCR products to those of beta-actin, changed with time during the late period of embryogenesis (day 10 to day 21). ERalpha-mRNA expression was observed at all ages examined in the present experiment. The expression increased between day 10 and day 15 of embryogenesis and then the value was decreased between day 15 and day 21 of embryogenesis. The numbers of ER-positive cells in the bursa also changed with time during the late period of embryogenesis (day 14 to day 18). ER-positive cells showed the highest level on day 14 of embryogenesis, and then the value declined. ER-positive cells were observed in lymphoid follicular cells, stromal cells and epithelial cells, and the density of ER-positive cells was highest in epithelial cells among the three cell components of the bursa. The high level of ER expression in the bursa of Fabricius (BF) of chick embryos at the late period of embryogenesis suggests that this stage of embryogenesis is critical in B cell differentiation in the bursa in connection with estrogen effects on antibody production after hatching.