Characterization of TRH/GnRH-like peptides in the sea cucumber, Holothuria scabra, and their effects on oocyte maturation

Abstract

Thyrotropin/Gonadotropin-releasing hormone (TRH/GnRH) is a neurohormone that plays important roles in regulation of several physiological processes of invertebrate species, including echinoderms. The aims of this study were to characterize for the first time a TRH/GnRH-like peptide in the sea cucumber, Holothuria scabra. We have isolated a full-length cDNA for a TRH/GnRH preprohormone gene from the radial nerve cord of H. scabra. We found that H. scabra (hs)TRH/GnRH precursor comprised two types of peptides, namely, the short TRH/GnRH-like peptides and the long TRH/GnRH-like peptides. The expression of hsTRH/GnRH gene, was intense in radial nerve cord, nerve ring and mature ovary by using RT-PCR. By in situ hybridization the transcripts of hsTRH/GnRH was detected at a high level within the late stages (oocyte stages 3 and 4). In the functional assays, injections of the short TRH/GnRH-like peptides could significantly accelerate gonadal development as reflected by increased gonadal-somatic index (GSI), and stimulated gametogenesis, as reflected by significantly increased oocyte proliferation. Taken together, our new discovery of the TRH/GnRH-like peptides in H. scabra contributes important new insights into the evolution of TRH/GnRH neuropeptide system in this sea cucumber species, and these neuropeptides could be potentially applied in the sea cucumber aquaculture.