Correlation between messenger RNA expression of cytochrome p450 aromatase and its enzyme activity during oocyte development in the red seabream (Pagrus major)

In teleosts, estradiol-17 beta (E-2) is an important hormone responsible fo r oocyte development. To elucidate the molecular mechanisms underlying E-2 biosynthesis, we characterized the structure of red seabream (Pagrus major) cytochrome P450 aromatase (P450(arom)) that is directly involved in E-2 bi osynthesis and found changes in mRNA levels of P450(arom) during oocyte dev elopment induced by implantation of gonadotropin-releasing hormone analogue . A cDNA clone encoding P450(arom) is 1779 base pairs in length and encodes a protein of 519 amino acids in length, with a calculated molecular weight of 58.9 kDa. Northern blot analysis showed that P450(arom) mRNA levels inc reased gradually from Day 8, when oocytes reached the secondary yolk globul e stage, and were maintained at high levels at the day of spawning (Day 15) . The P450(arom) mRNA levels increased in association with an increase of t he gonadosomatic index (gonad weight/body weight x 100%), serum E-2, and P4 50(arom) enzyme activity (in vitro conversion of testosterone to E-2 in the ovarian fragments). Furthermore, an increase in mRNA levels of the LH beta , but not FSH beta, correlated with increased P450(arom) mRNA levels during the course of ovarian development. in addition, the levels of P450(arom) m RNA increased in isolated ovarian follicles during the course of vitellogen ic oocyte growth and became undetectable in follicles at the migratory nucl eus and the mature stages. These findings, together with those of the previ ous studies, suggest that LH, not FSH, may regulate E-2 biosynthesis via in creased levels of P450(arom) mRNA during oocyte development of red seabream .