Aromatase (Cyp19a1b) in the Pituitary Is Dynamically Involved in the Upregulation of lhb But Not fshb in the Vitellogenic Female Ricefield Eel Monopterus albus

Aromatase, encoded by Cyp19a1, is expressed in the pituitary of vertebrates; however, its physiological relevance remains poorly defined. In teleosts, the duplicated cyp19a1b is preferentially expressed in the pituitary where LH and FSH are synthesized in distinct gonadotropes. Our present study demonstrated that Cyp19a1b is colocalized with Lhb, but not Fshb, during vitellogenesis in female ricefield eels. The immunoreactive levels of Cyp19a1b and Lhb, as well as their colocalization frequency, increased during vitellogenesis toward maturation. The expression of lhb but not fshb in the pituitary fragments of female ricefield eels was induced by both estradiol (E2) and testosterone (T). In agreement, the promoter of lhb but not fshb was activated by both E2 and T. T is more potent than E2 in inducing lhb expression, whereas E2 is much more effective in activating the lhb promoter. T-induced lhb expression in the pituitary fragments was abolished by the estrogen receptor (Esr) antagonist fulvestrant and su...