Identification and characterization of neuropeptides in sea urchin Strongylocentrotus intermedius

Neuropeptides play essential roles in regulation of feeding, reproduction and behavior in echinoderms. But the neuropeptide function has not been explored extensively in sea urchins. The tube feet contain part of the peripheral nervous system in echinoids, comprising both neurosensory and neuromuscular components. In this study, we sequenced transcriptome of Strongylocentrotus intermedius tube feet and identified 26 neuropeptide precursor transcripts, including ANpeptide, bursicons, calcitonin, corazonin, gonadotropin-releasing hormone (GnRH), glycoprotein-type hormones (GPA & GPB), insulin-related peptides (dilp7 & octinsulin), luqin, NGFFFamide, prolactin-releasing peptide/short neuropeptide F (PrRP/sNPF), orexin, pedal peptides, SALMFamides, somatostatin/allatostatin-C (SS1 & SS2), thyrotropin-releasing hormone (TRH), and vasopressin-oxytocin. In addition, we further compared the expression levels of neuropeptide precursors between red and white tube feet, and found 3 neuropeptides (bursicon β, octinsulin and luqin) had higher expression in red tube feet, potentially related to pigmentation or other pigment-related functions. We also observed ultrastructure of tube feet by transmission electron microscopy (TEM) and found large amount of muscle fibers, nerve plexus and vesicles in tube feet. Neuropeptides might play roles in these structures of tube feet. Our study represents the first identification of neuropeptides in tube feet of S. intermedius, and will contribute to a complete understanding on the roles of various neuropeptides in sea urchin echinoderms.