Characterization of an abalone gonadotropin-releasing hormone and its effect on ovarian cell proliferation

In various animal groups, both vertebrates and invertebrates, it has been reported that gonadotropin-releasing hormone (GnRH) is an important regulator of reproductive function. Knowledge of the molecular identity of a GnRH and its function in the abalone is unknown. In this study, we have characterized the abalone GnRH genes and their putative precursor sequences from the neural ganglia of sexually mature female Haliotis asinina and Haliotis laevigata. The abalone GnRH genes demonstrate high similarity with other gastropods within the proposed bioactive GnRH peptide regions (H. asinina: QNYHFSNGWYPG; H. laevigata: QNYHFSNGWHA) but less in the GnRH-associated peptide region. An antibody generated against HasGnRH showed specific expression of the peptide within the cerebral and pleuropedal ganglia. HasGnRH was localized in type-1 neurosecretory cells that are widely distributed within the ventral and dorsal parts of the cerebral ganglion and also observed in nerve fiber bundles extending into the dorsal part of the ganglion. In the pleuropedal ganglion, HasGnRH immunoreactive cells were distributed in both ventral and dorsal horns. Nerve fibers containing HasGnRH immunoreactivity were also detected primarily within the ventral region of ventral horns of the ganglion. Synthetic HasGnRH and buserelin stimulated oogonia and oocyte proliferation in one-year-old female H. asinina as determined by in vivo and in vitro BrdU ovarian cell proliferation. These findings provide important knowledge into the molecular identity of the abalone GnRH and its function in stimulating oocyte proliferation that helps us to further understand the role of this peptide in molluscs which may be applied to aquaculture of this species.