In vitro study of a putative role of gonad-inhibiting hormone in oocyte growth stimulation inPenaeus monodon

Abstract

Ovarian development in crustacean is controlled by several factors, among which a neuropeptide gonad-inhibiting hormone (GIH) is known to inhibit vitellogenin (Vg) synthesis in the ovary. It has been postulated that GIH may control Vg synthesis by inhibiting the release of gonad-stimulating factor (GSF) from brain and thoracic ganglia. To prove this hypothesis, this study was primarily aimed to investigate the influence of GIH on the release of GSF from thoracic ganglia of Penaeus monodon. Our result showed that GIH did not suppress the release of putative GSF from thoracic ganglia by calcium ionophore A23187 as the induction of oocyte growth in the ovary explants that were cocultured with thoracic ganglia in the presence of A23187 was not affected by the addition of recombinant GIH protein. In addition and interestingly, when the ovary explants were incubated with the recombinant GIH alone, the oocyte growth was increased at the rate comparable to that induced by A23187 in the presence of thoracic ganglia. Hence, our in vitro study demonstrated that the stimulation of GSF released from thoracic ganglia is independent of GIH, and that the GIH has a dual function in oocyte growth stimulation and inhibition of Vg synthesis in the early stage of ovarian development. This expands our knowledge on the regulation of ovarian development in shrimp by GIH. Further in vivo studies in this novel aspect of GIH function will be useful for the improvement of shrimp ovarian maturation in the future.