Differential expression of three estrogen receptors mRNAs in tissues, growth development, embryogenesis and gametogenesis from large yellow croaker, Larimichthys crocea.

The biological activity of estrogens in target organs is mainly mediated by estrogen receptors (ERs). Herein, we addressed the isolation and expression analysis of three nuclear estrogen receptors, namely LcERα, LcERβ1, and LcERβ2 from Larimichthys crocea by means of SMART-RACE, qRT-PCR, and in situ hybridization. Results in different tissues showed that both LcERα and LcERβ2 had the highest expression levels in female liver, followed by testis, but LcERβ1 expression level was significantly higher in testis and ovary than in other tissues. Expression of LcERα and LcERβ2 was significantly higher than LcERβ1 in female liver, and LcERβ2 was significantly higher than LcERα and LcERβ1 in male liver. Moreover, we analyzed the expression of LcERs in gonad and liver at three different growth stages during the same breeding season. Significant up-regulated expression of LcERα and LcERβ2 were found in female liver at 1000dph compared with at 270dph. The expression of LcERβ2 was prominently higher in male liver than LcERα, LcERβ1 and LcAR, while LcERβ1 was lower than other receptors in male and female liver at all the three stages. In ovary, LcERα at 270dph was lower than at 635dph and 1000dph, but had no significant change in testis. The two LcERβ subtypes and LcAR highly expressed in the early testis, and gradually decrease with the development of testis. In embryogenesis, a significant increase in the expression of LcERα and LcERβ2 were observed after appearance of optic vesicles phase (11.8hpf). LcERβ1 gradually decrease with the embryogenesis but increased dramatically at 1dph. Results of in situ hybridization showed that signals of LcERα and LcERβ1 mRNA were mainly detected in Stage I-Stage IV oocytes, as well as in follicle cells around the Stage II-Stage IV and degenerated oocytes. Signals of LcERβ2 were detected in the cytoplasm of Stage I and Stage II oocytes but not in the follicle cells of all oocytes stages. In parallel, LcERα and LcERβ1 were detected in all cell types of spermatogenesis, but in terms of LcERβ2, little or no signals were detected during spermatogenesis. Based on these results, we deduced that both LcERα and LcERβ2 play a major role in mediating the physiological effects of estrogen in female liver, and LcERβ2 maybe also play an important role in regulation of vitellogenesis in male liver. Differential expression of LcERs and LcAR imply their physiological functions during development and differentiation of gonad. The signals for LcERα and LcERβ1 in follicle cells suggested that the follicle cell maybe an important site of estrogen action, by which estrogens exert influences on the maturation oocytes and ovulation. Furthermore, the steroid hormones produced by follicle cells may be related to the differential distributions among ER subtypes. Besides, we deduced that LcERα and LcERβ1 rather than LcERβ2 may play a major role in spermatogenesis of croaker. However, the differential expression of LcERβ2 during gametogenesis also implicates its certain functions in mediating physiological process of estrogen action.