EXPRESSION OF THE CRUSTACEAN HYPERGLYCEMIC HORMONES AND THE GONAD-INHIBITING HORMONE DURING THE REPRODUCTIVE-CYCLE OF THE FEMALE AMERICAN LOBSTER HOMARUS-AMERICANUS

Crustacean reproduction is regulated by a complex chain of hormonal in teractions in which the crustacean hyperglycaemic hormones A and B (CH H-A and CHH-B) and the gonad-inhibiting hormone (GIH) play a primary r ole. These neurohormones are produced in the same neuroendocrine cells of the X-organ sinus gland complex, situated in the eyestalks of the American lobster, Homanus americanus. In order to obtain more informat ion on the synthesis, storage, release and function of these three neu ropeptides during the reproductive cycle, we studied the levels of the ir mRNAs in the X-organ, their peptide storage in the sinus gland and their concentration in the haemolymph at different stages of the femal e reproductive cycle. A high CHH-A mRNA level was found only in the pr evitellogenic stage, while elevated mRNA levels were determined for CH H-B in the mature as well as the previtellogenic stage. High CHH stora ge levels in the sinus gland were found during previtellogenesis. The total amount of CHH (CHH-A plus -B) in the haemolymph was significantl y higher during maturation. A low level of GIH mRNA in the X-organ and a low amount of the GIH I isoform in the sinus gland were found only in the immature stage. In contrast, GIH haemolymph levels were high du ring the immature and previtellogenic stages. We conclude that CHH-A a nd -B are involved in triggering the onset of vitellogenesis and that CHH-B in particular is responsible for stimulating oocyte maturation b efore spawning, while GIH prevents the start of vitellogenesis in the ovary. Moreover, our results show that the balance between the haemoly mph levels of the CHHs and GIH may tune the synchronization of reprodu ction and molting during the biannual reproductive cycle of the Americ an lobster.