Abstract
The neuropeptides involved in the regulation of reproduction in the Pacific oyster (Crassostrea gigas) are quite diverse. To investigate this diversity, a transcriptomic survey of the visceral ganglia (VG) was carried out over an annual reproductive cycle. RNA-seq data from 26 samples corresponding to VG at different stages of reproduction were de novo assembled to generate a specific reference transcriptome of the oyster nervous system and used to identify differentially expressed transcripts. Transcriptome mining led to the identification of novel neuropeptide precursors (NPPs) related to the bilaterian Eclosion Hormone (EH), crustacean female sex hormone/Interleukin 17, Nesfatin, neuroparsin/IGFBP, prokineticins, and urotensin I; to the protostome GNQQN, pleurin, prohormones 3 and 4, prothoracotropic hormones (PTTH), and QSamide/PXXXamide; to the lophotrochozoan CCWamide, CLCCY, HFAamide, and LXRX; and to the mollusk-specific NPPs CCCGS, clionin, FYFY, GNamide, GRWRN, GSWN, GWE, IWMPxxGYxx, LXRYamide, RTLFamide, SLRFamide, and WGAGamide. Among the complete repertoire of NPPs, no sex-biased expression was observed. However, 25 NPPs displayed reproduction stage-specific expression, supporting their involvement in the control of gametogenesis or associated metabolisms.
Highlights
As sessile organisms living in estuaries and intertidal zones, Pacific oysters (Crassostrea gigas) are resilient to highly stressful and widely changing environmental conditions [1,2,3]
Gigas, the present study provides an overview of the neuropeptide precursors (NPPs)/peptide precursors (PPs) expressed in this species, with the characterization of 44 new NPPs
Our results confirm that NPs hitherto presumed to be specific to ecdysozoan species—e.g., orthologs of ecdysis-regulated NPs or arthropod reproduction-regulated hormones—are present in C. gigas, confirming their early evolutionary origin
Summary
As sessile organisms living in estuaries and intertidal zones, Pacific oysters (Crassostrea gigas) are resilient to highly stressful and widely changing environmental conditions [1,2,3]. They are exposed daily to large variations in food supply, oxygen, temperature, and salinity over the tidal cycle. They can tolerate extended periods of emersion. To cope with these adverse conditions, oysters do not develop complex behavioral responses like many free-living animals do, but adapt their physiological processes and their metabolism. As neuron-secreted specific signaling peptides, neuropeptides (NPs) represent essential components of neural communication, and play a major role in these regulatory processes
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