Functional analysis and localisation of a thyrotropin-releasing hormone-type neuropeptide (EFLa) in hemipteran insects

Characterization of thyrotropin-releasing hormone producing neurons in sea urchin, from larva to juvenile

Most sea urchin species are indirect developers, going through a larval stage called pluteus. The pluteus possesses its own nervous system, consisting mainly of the apical organ neurons (controlling metamorphosis and settlement) and ciliary band neurons (controlling swimming behavior and food collection). Additional neurons are located in various areas of the gut. In recent years, the molecular complexity of this apparently "simple" nervous system has become apparent, with at least 12 neuronal populations identified through scRNA-sequencing in the species Strongylocentrotus purpuratus. Among these, there is a cluster of neurosecretory cells that produce a thyrotropin-releasing hormone-type neuropeptide (TRHergic) and that are also photosensory (expressing a Go-Opsin). However, much less is known about the organization of the nervous system in other sea urchin species. The aim of this work was to thoroughly characterize the localization of the TRHergic cells from early pluteus to juvenile stages in the Mediterranean sea urchin species Paracentrotus lividus combining immunostaining and whole mount in situ hybridization. We also compared the localization of TRHergic cells in early plutei of two other sea urchin species, Arbacia lixula and Heliocidaris tuberculata. This work provides new information on the anatomy and development of the nervous system in sea urchins. Moreover, by comparing the molecular signature of the TRHergic cells in P. lividus and S. purpuratus, we have obtained new insights how TRH-type neuropeptide signaling evolved in relatively closely related species.

Best Practices for Comprehensive Annotation of Neuropeptides of Gryllus bimaculatus

Genome annotation is critically important data that can support research. Draft genome annotations cover representative genes; however, they often do not include genes that are expressed only in limited tissues and stages, or genes with low expression levels. Neuropeptides are responsible for regulation of various physiological and biological processes. A recent study disclosed the genome draft of the two-spotted cricket Gryllus bimaculatus, which was utilized to understand the intriguing physiology and biology of crickets. Thus far, only two of the nine reported neuropeptides in G. bimaculatus were annotated in the draft genome. Even though de novo assembly using transcriptomic analyses can comprehensively identify neuropeptides, this method does not follow those annotations on the genome locus. In this study, we performed the annotations based on the reference mapping, de novo transcriptome assembly, and manual curation. Consequently, we identified 41 neuropeptides out of 43 neuropeptides, which were reported in the insects. Further, 32 of the identified neuropeptides on the genomic loci in G. bimaculatus were annotated. The present annotation methods can be applicable for the neuropeptide annotation of other insects. Furthermore, the methods will help to generate useful infrastructures for studies relevant to neuropeptides.

Neuropeptides in Rhipicephalus microplus and other hard ticks

The synganglion is the central nervous system of ticks and, as such, controls tick physiology. It does so through the production and release of signaling molecules, many of which are neuropeptides. These peptides can function as neurotransmitters, neuromodulators and/or neurohormones, although in most cases their functions remain to be established. We identified and performed in silico characterization of neuropeptides present in different life stages and organs of Rhipicephalus microplus, generating transcriptomes from ovary, salivary glands, fat body, midgut and embryo. Annotation of synganglion transcripts led to the identification of 32 functional categories of proteins, of which the most abundant were: secreted, energetic metabolism and oxidant metabolism/detoxification. Neuropeptide precursors are among the sequences over-represented in R. microplus synganglion, with at least 5-fold higher transcription compared with other stages/organs. A total of 52 neuropeptide precursors were identified: ACP, achatin, allatostatins A, CC and CCC, allatotropin, bursicon A/B, calcitonin A and B, CCAP, CCHamide, CCRFamide, CCH/ITP, corazonin, DH31, DH44, eclosion hormone, EFLamide, EFLGGPamide, elevenin, ETH, FMRFamide myosuppressin-like, glycoprotein A2/B5, gonadulin, IGF, inotocin, insulin-like peptides, iPTH, leucokinin, myoinhibitory peptide, NPF 1 and 2, orcokinin, proctolin, pyrokinin/periviscerokinin, relaxin, RYamide, SIFamide, sNPF, sulfakinin, tachykinin and trissin. Several of these neuropeptides have not been previously reported in ticks, as the presence of ETH that was first clearly identified in Parasitiformes, which include ticks and mites. Prediction of the mature neuropeptides from precursor sequences was performed using available information about these peptides from other species, conserved domains and motifs. Almost all neuropeptides identified are also present in other tick species. Characterizing the role of neuropeptides and their respective receptors in tick physiology can aid the evaluation of their potential as drug targets.

Cryptochrome-dependent magnetoreception in a heteropteran insect continues even after 24 h in darkness

Sensitivity to magnetic fields is dependent on the intensity and color of light in several animal species. The light-dependent magnetoreception working model points to cryptochrome (Cry) as a protein cooperating with its co-factor flavin, which possibly becomes magnetically susceptible upon excitation by light. The type of Cry involved and what pair of magnetosensitive radicals are responsible is still elusive. Therefore, we developed a conditioning assay for the firebug Pyrrhocoris apterus, an insect species that possesses only the mammalian cryptochrome (Cry II). Here, using the engineered Cry II null mutant, we show that: (i) vertebrate-like Cry II is an essential component of the magnetoreception response, and (ii) magnetic conditioning continues even after 25 h in darkness. The light-dependent and dark-persisting magnetoreception based on Cry II may inspire new perspectives in magnetoreception and cryptochrome research.

Filling in the gaps: A reevaluation of the Lygus hesperus peptidome using an expanded de novo assembled transcriptome and molecular cloning

Peptides are the largest and most diverse class of molecules modulating physiology and behavior. Previously, we predicted a peptidome for the western tarnished plant bug, Lygus hesperus, using transcriptomic data produced from whole individuals. A potential limitation of that analysis was the masking of underrepresented genes, in particular tissue-specific transcripts. Here, we reassessed the L. hesperus peptidome using a more comprehensive dataset comprised of the previous transcriptomic data as well as tissue-specific reads produced from heads and accessory glands. This augmented assembly significantly improves coverage depth providing confirmatory transcripts for essentially all of the previously identified families and new transcripts encoding a number of new peptide precursors corresponding to 14 peptide families. Several families not targeted in our initial study were identified in the expanded assembly, including agatoxin-like peptide, CNMamide, neuropeptide-like precursor 1, and periviscerokinin. To increase confidence in the in silico data, open reading frames of a subset of the newly identified transcripts were amplified using RT-PCR and sequence validated. Further PCR-based profiling of the putative L. hesperus agatoxin-like peptide precursor revealed evidence of alternative splicing with near ubiquitous expression across L. hesperus development, suggesting the peptide serves functional roles beyond that of a toxin. The peptides predicted here, in combination with those identified in our earlier study, expand the L. hesperus peptidome to 42 family members and provide an improved platform for initiating molecular and physiological investigations into peptidergic functionality in this non-model agricultural pest.

Genomics- and Peptidomics-Based Discovery of Conserved and Novel Neuropeptides in the American Cockroach

As a model hemimetabolous insect species and an invasive urban pest that is globally distributed, the American cockroach, Periplaneta americana, is of great interest in both basic and applied research. Previous studies on P. americana neuropeptide identification have been based on biochemical isolation and molecular cloning. In the present study, an integrated approach of genomics- and peptidomics-based discovery was performed for neuropeptide identification in this insect species. First, 67 conserved neuropeptide or neurohormone precursor genes were predicted via an in silico analysis of the P. americana genome and transcriptome. Using a large-scale peptidomic analysis of peptide extracts from four different tissues (the central nervous system, corpora cardiac and corpora allata complex, midgut, and male accessory gland), 35 conserved (predicted) neuropeptides and a potential (novel) neuropeptide were then identified. Subsequent experiments revealed the tissue distribution, sex difference, and developmental patterns of two conserved neuropeptides (allatostatin B and short neuropeptide F) and a novel neuropeptide (PaOGS36577). Our study shows a comprehensive neuropeptidome and detailed spatiotemporal distribution patterns, providing a solid basis for future functional studies of neuropeptides in the American cockroach (data are available via ProteomeXchange with identifier PXD021660).

Gonadulins, the fourth type of insulin-related peptides in decapods

Insulin and related peptides play important roles in the regulation of growth and reproduction. Until recently three different types of insulin-related peptides had been identified from decapod crustaceans. The identification of two novel insulin-related peptides from Sagmariasus verreauxi and Cherax quadricarinatus suggested that there might a fourth type. Publicly available short read archives show that orthologs of these peptides are commonly present in these animals. Most decapods have two genes coding such peptides, but Penaeus species have likely only one and some palaemonids have three. Interestingly, expression levels can vary more than thousand-fold in the gonads of Portunus trituberculatus, where gonadulin 1 is expressed by the testis and gonadulin 2 by the ovary. Although these peptides are also expressed in other tissues, the occasionally very high expression in the gonads led to them being called gonadulins.