Estrogen receptor-alpha and -beta mRNA expression in medullary bone or Japanese quail
2004
Imamura, T. | Sugiyama, T. | Kusuhara, S.
Medullary bone, a specific tissue for female birds, plays an important role as a calcium reservoir for eggshell formation. The medullary bone is a target tissue of estrogen, and their formation is readily induced by the treatment of matured male birds with estrogen. However, the function of estrogen receptor (ER) -alpha and -beta in medullary bone metabolism has not been fully clarified. Therefore, the present study was conducted to examine the kinetics ofER-alpha and -beta mRNA expression during the medullary bone formation and resorption of male Japanese quail treated with estrogen. Before the injection of estradiol, there was no medullary bone in marrow cavities of femurs. After the single injection of estradiol (estradiol valerate 2 mg / 100 g body weights), the medullary bone was observed on the endosteal surface of the cortical bone at 48 hours and highly developed into marrow cavities up to 144 hours. During these periods, differentiated osteoblasts actively formed bone matrix. Thereafter, the medullary bone was resorbed by multinucleated osteoclasts, and consequently disappeared entirely at 288 hours. In according to these formation and resorption of the medullary bone, the kinetics of ER-alpha and -beta mRNA expression were examined with semiquantitative RT-PCR analysis. As a result, after the single injection of estradiol, the expression of ERalpha mRNA was increased and reached into a peak at 144 hours. After them, the expression of ER-alpha was decreased, and returned to that before the injection. On the other hand, the expression of ER-beta mRNA did not change during the time course experimented here. In conclusion, these results suggested that ER-alpha plays an important role for osteoblastic formation of medullary bone.
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