THE PRESENCE AND ROLES OF GONADOTROPINRELEASING HORMONE IN THE REPRODUCTION OF CORALS

Abstract

In southern Taiwan, the mass spawning of scleractinian corals occurs yearly in lunar mid-March. Our previous studies shown that peak levels of estradiol (E2) and aromatase activity in corals during the spawning period. We hypothesize that the endocrine system, especially gonadotropin- releasing hormone (GnRH) plays an important role as the endogenous factor in the synchronous mass spawning of scleractinian corals, using Euphyllia ancora as a model species. The investigation of the presence, bioactivity in the regulation of luteinizing hormone (LH) release, annual cycle and the possible roles in the reproduction of GnRH were conducted. Coral polyps were extracted with acid solution and purified by a Sep-Pak C-18 cartridge column and HPLC, GnRH was measured by a validated radioimmunoassay. Immunoreactive GnRH was consistently detected in female and male coral tissue throughout 3-year period. Positive GnRH neurons were immunohistochemically stained in the corals. Peak concentrations of GnRH were obtained in the coral tissue just prior to spawning with a 10-fold increase as compared to the non-spawning season. The primary culture of pituitary cells was further developed in black porgy fish to examine the activity of coral GnRH in the regulation of LH release. Coral GnRH extracts and mGnRH analog could similarly stimulate LH release from dispersed black porgy pituitary cells at a dosedependent manner, respectively. GnRH antagonist significantly and dosedependently inhibited the stimulation of LH release in response to coral extracts and mGnRH analog. mGnRH analog could significantly stimulate the increase of aromatase activity, testosterone and E2 concentrations, and steroid glucuronization in corals. Exogenous GnRH further stimulated the oocyte growth of corals. Seasonal variation of coral GnRH, with a dramatic increase during the spawning period, concomitant to that in aromatase and sex steroids, as well as the ability of mGnRH agonist to stimulate coral aromatase, steroidogenesis, and steroid glucuronization suggest that GnRH plays an ancestral role in the control of oocyte growth and mass spawning in corals. (poster)