Effect of gonadotropin releasing hormone on the expression of luteinizing hormone and estrogen in the nerve ganglia and ovary of a tropical abalone, Haliotis asinina Linnaeus

The occurrence of luteinizing hormone-like molecule and its receptor in the blue swimming crab, Portunus pelagicus

Knowledge of the neuroendocrine system possibly improves the reproductive performance of captivated crustacean broodstock in aquaculture and it may substitute eyestalk ablation. In this study, we explored the luteinizing hormone (LH)-like molecule and proved the existence of the LH receptor (PpelLHR)-like mRNA in the blue swimming crab, Portunus pelagicus. Using the anti-human LH-β antibody, the immunoreactivities were found in the central nervous system (CNS) and ovary of the crab with the strongest signal in the mature ovary. The full-length PpelLHR-like mRNA sequence contained 4818 bp with deduced protein predicted as seven transmembrane G-protein coupled receptor, made of 1605 amino acids. The phylogenetic tree suggested this protein belonged to the clade of invertebrate LHR/FSHR-like proteins. The PpelLHR-like mRNA expressed in various organs and real-time qPCR revealed significantly higher expression of this mRNA in the brain and lower expression in the ovary of the mature crabs. In situ hybridization of this mRNA was demonstrated in neuronal clusters of the brain, ventral nerve cord, and in the oocyte stage 1-4 of the ovary, respectively. This study was preliminary to prove the existence of LH and its receptor in the blue swimming crab. Functional assay of this receptor should be performed as the next part of experiments to firmly conclude its appearance.

Identification and characterization of gonadotropin-releasing hormone (GnRH) in Zhikong scallop Chlamys farreri during gonadal development

Gonadotropin-releasing hormone (GnRH) controls synthesis of sex steroid hormones through hypothalamic-pituitary-gonadal (HPG) axis in vertebrates. But in mollusks, research on neuroendocrine control of gonadal function, such as the function of GnRH during gonadal development is limited. In this study, we investigated the morphology and structure of the nerve ganglia of Zhikong scallop Chlamys farreri by physiological and histological observations. We also cloned the ORF and studied the expression patterns of GnRH in the scallop. Tissue expression analysis showed that GnRH was highly expressed in parietovisceral ganglion (PVG). The in situ hybridization result further confirmed that GnRH mRNA only distributed in some good-sized neurons in the posterior lobe (PL) and some pint-sized neurons in the lateral lobe (LL). In addition, by examining the expression of GnRH during gonadal development in ganglia, we found GnRH displayed higher expression in the female scallops, and showed significant high expression at the growing stage of female scallops in PVG. This study would contribute to gaining insight into the mechanism underlying reproduction regulation by GnRH in the scallop and help to provide a better understanding of reproductive neuroendocrine in mollusks.

A critical evaluation of some of the recent so-called 'evidence' for the involvement of vertebrate-type sex steroids in the reproduction of mollusks

Many studies on the control of reproduction in mollusks have focused on hormones (and proteins associated with the production and signaling of those hormones) which were originally discovered in humans, in the belief that if they are also present in mollusks, they must have the same role. However, although human sex steroids can be found in mollusks, they are so readily absorbed that their presence is not necessarily evidence of endogenous synthesis. A homolog of the vertebrate nuclear estrogen receptor has been found in mollusks, but it does not bind to estrogens or indeed to any steroid at all. Antibodies against human aromatase show positive immunostaining in mollusks, yet the aromatase gene has not been found in the genome of any invertebrates (let alone mollusks). This review will deal with these and other examples of contradictory evidence for a role of human hormones in invertebrate reproduction.