In Vivo Administration of Scallop GnRH-Like Peptide Influences on Gonad Development in the Yesso Scallop, Patinopecten yessoensis

Abstract

Existing research on the role of gonadotropin-releasing hormone (GnRH) in bivalve reproduction is inadequate, even though a few bivalve GnRH orthologs have been cloned. The objective of this paper was to elucidate the in vivo effect of GnRH administration in Yesso scallop reproduction. We performed in vivo administration of scallop GnRH (py-GnRH) synthetic peptide into the developing gonad, and analyzed its effect on gonad development for 6 weeks during the reproductive season. The resulting sex ratio in the GnRH administered (GnRH(+)) group might be male biased, whereas the control (GnRH(-)) group had an equal sex ratio throughout the experiment. The gonad index (GI) of males in the GnRH(+) group increased from week 2 to 24.8% at week 6. By contrast the GI of the GnRH(-) group peaked in week 4 at 16.6%. No significant difference was seen in female GI between the GnRH(+) and GnRH(-) groups at any sampling point. Oocyte diameter in the GnRH(+) group remained constant (about 42–45 μm) throughout the experiment, while in the GnRH(-) group it increased from 45 to 68 μm i.e. normal oocyte growth. The number of spermatogonia in the germinal acini of males in the GnRH(+) group increased from week 4 to 6. Hermaphrodites appeared in the GnRH(+) group in weeks 2 and 4. Their gonads contained many apoptotic cells including oocytes. In conclusion, this study suggests that py-GnRH administration could have a potential to accelerate spermatogenesis and cause an inhibitory effect on oocyte growth in scallops.

Identification and Characterization of Neuropeptides by Transcriptome and Proteome Analyses in a Bivalve Mollusc Patinopecten yessoensis

“…In Aplysia , GnRH seems to regulate behaviors, but fails to induce gonadal maturation ( Tsai et al, 2010 ; Sun and Tsai, 2011 ). In scallop P. yessoensis , GnRH can cause an inhibitory effect on oocyte growth and stimulate spermatogonial proliferation ( Nakamura et al, 2007 ; Nagasawa et al, 2015a ). The lack of a solid connection between reproduction and mollusc GnRH suggests that mollusc GnRH may serve as a general neural regulator which may or may not involve reproduction.…”

“…Several studies reveal that molecular signals from nerve ganglia play vital roles in scallop gonadal development. For example, it is reported that neurotransmitters, such as GABA and glycine, may participate in scallop ovary development ( Li et al, 2016 ), and GnRH can stimulate spermatogonial proliferation ( Nakamura et al, 2007 ) and inhibit oocyte growth ( Nagasawa et al, 2015a ). But till now, no systematic identification of neuropeptides has been performed.…”

Systematic identification and validation of the reference genes from 60 RNA-Seq libraries in the scallop Mizuhopecten yessoensis

“…Bivalve mollusks comprise approximately 14,000 existing species that are widely distributed worldwide. Many of these species are economically important aquaculture shellfish; therefore, extensive studies on the genes related to immunity [18][19][20], growth [21][22][23] and reproduction [24,25] have been conducted in this group of animals. Gene expression quantification via RT-qPCR has been extensively conducted, but mostly using a single reference gene, such as ACT and CYTC [26][27][28].…”

FOXL2 and DMRT1L Are Yin and Yang Genes for Determining Timing of Sex Differentiation in the Bivalve Mollusk Patinopecten yessoensis

“…It is predominantly gonochoric, with scarce hermaphroditism. Due to its commercial importance, much work has been performed to obtain an understanding of its reproductive process ( Osada et al, 2004 ; Tanabe et al, 2010 ; Nagasawa et al, 2015 ). Recently, our group completed whole genome sequencing and gonadal transcriptome analysis of P. yessoensis ( Li et al, 2016 ; Wang et al, 2017 ), which provide valuable resources for unraveling the molecular mechanisms underlying scallop sex differentiation.…”