Neuropeptidergic Signaling in the American Lobster Homarus americanus: New Insights from High-Throughput Nucleotide Sequencing

Abstract

Peptides are the largest and most diverse class of molecules used for neurochemical communication, playing key roles in the control of essentially all aspects of physiology and behavior. The American lobster, Homarus americanus, is a crustacean of commercial and biomedical importance; lobster growth and reproduction are under neuropeptidergic control, and portions of the lobster nervous system serve as models for understanding the general principles underlying rhythmic motor behavior (including peptidergic neuromodulation). While a number of neuropeptides have been identified from H. americanus, and the effects of some have been investigated at the cellular/systems levels, little is currently known about the molecular components of neuropeptidergic signaling in the lobster. Here, a H. americanus neural transcriptome was generated and mined for sequences encoding putative peptide precursors and receptors; 35 precursor- and 41 receptor-encoding transcripts were identified. We predicted 194 distinct neuropeptides from the deduced precursor proteins, including members of the adipokinetic hormone-corazonin-like peptide, allatostatin A, allatostatin C, bursicon, CCHamide, corazonin, crustacean cardioactive peptide, crustacean hyperglycemic hormone (CHH), CHH precursor-related peptide, diuretic hormone 31, diuretic hormone 44, eclosion hormone, FLRFamide, GSEFLamide, insulin-like peptide, intocin, leucokinin, myosuppressin, neuroparsin, neuropeptide F, orcokinin, pigment dispersing hormone, proctolin, pyrokinin, SIFamide, sulfakinin and tachykinin-related peptide families. While some of the predicted peptides are known H. americanus isoforms, most are novel identifications, more than doubling the extant lobster neuropeptidome. The deduced receptor proteins are the first descriptions of H. americanus neuropeptide receptors, and include ones for most of the peptide groups mentioned earlier, as well as those for ecdysis-triggering hormone, red pigment concentrating hormone and short neuropeptide F. Multiple receptors were identified for most peptide families. These data represent the most complete description of the molecular underpinnings of peptidergic signaling in H. americanus, and will serve as a foundation for future gene-based studies of neuropeptidergic control in the lobster.

Deep sequencing of transcriptomes from the nervous systems of two decapod crustaceans to characterize genes important for neural circuit function and modulation

“…Based on the relative similarity in many of the metrics for these two assembly methods, the somewhat better performance of CLC contigs when compared with Sanger sequencing generated orthologs, and the fact that portions of the H. americanus transcriptome based on the CLC assembly have previously been published [4], we chose to perform the remaining representative analysis of these sequence data based on the CLC assembled contigs. The H. americanus Transcriptome Shotgun Assembly (TSA) project has been deposited at GenBank under Accession No.…”

“…In particular, classic preparations such as the Tritonia swim system [107], Aplysia feeding circuits as well as the classic gill and siphon withdrawal reflex [108, 109], and crustacean stomatogastric systems [19] revolutionized our understanding of neural circuitry. Each of these systems is the renewed focus of genomic and transcriptomic approaches [4, 5, 110, 111] – including this study – that promise to merge the unparalleled experimental accessibility on the neurophysiology end of the spectrum with new molecular tools to understand and manipulate these circuits. Decapod crustacean systems have also been foundational in the understanding of modulation of behavioral states.…”

“…Since then, a mixed tissue transcriptome sequencing projects have been performed from the spider crab, Hyas araneus [118, 119] and spiny lobster Sagmariasus verreauxi [120]. Some of the most proactive work in crustacean transcriptomics lies in the area of neuropeptidomics for the discovery of neuroactive peptides and their receptors [121–124], including a study that makes use of the H. americanus sequence data contained reported here [4]. However, none of these studies provides analysis of ion channel or receptor sequence as contained within our study.…”

“…As a microcrustacean, Daphnia is still a far cry from the large decapod crustaceans that are common models in neuroscience research, such as crabs, lobsters, crayfish and shrimp. Thus even with some very recent additions to decapod crustacean transcriptome data [4, 5], there is a strong need to add to our sequence knowledge of these species.…”

Neuropeptide modulation of pattern-generating systems in crustaceans: comparative studies and approaches

“…Pattern-generating networks in crustaceans are extensively modulated by amines and neuropeptides, with the number of identified neuropeptides in many species nearing or exceeding 100 (eg [1*–5]). While the functions of many neuropeptides remain unknown, some peptides are able to modulate pattern-generating networks; these modulatory inputs enable the circuits to produce a plethora of different motor patterns.…”