Identification of two capa cDNA transcripts and detailed peptidomic characterization of their peptide products in Periplaneta americana

Transcriptomic, peptidomic, and mass spectrometry imaging analysis of the brain in the ant Cataglyphis nodus

Behavioral flexibility is an important cornerstone for the ecological success of animals. Social Cataglyphis nodus ants with their age-related polyethism characterized by age-related behavioral phenotypes represent a prime example for behavioral flexibility. We propose neuropeptides as powerful candidates for the flexible modulation of age-related behavioral transitions in individual ants. As the neuropeptidome of C. nodus was unknown, we collected a comprehensive peptidomic data set obtained by transcriptome analysis of the ants' central nervous system combined with brain extract analysis by Q-Exactive Orbitrap mass spectrometry (MS) and direct tissue profiling of different regions of the brain by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS. In total, we identified 71 peptides with likely bioactive function, encoded on 49 neuropeptide-, neuropeptide-like, and protein hormone prepropeptide genes, including a novel neuropeptide-like gene (fliktin). We next characterized the spatial distribution of a subset of peptides encoded on 16 precursor proteins with high resolution by MALDI MS imaging (MALDI MSI) on 14 µm brain sections. The accuracy of our MSI data were confirmed by matching the immunostaining patterns for tachykinins with MSI ion images from consecutive brain sections. Our data provide a solid framework for future research into spatially resolved qualitative and quantitative peptidomic changes associated with stage-specific behavioral transitions and the functional role of neuropeptides in Cataglyphis ants.

The neuropeptidome of Carabus (Coleoptera, Adephaga: Carabidae)

Neuropeptides are signaling molecules involved in the regulation of virtually all physiological functions of Metazoa. In insects, more than 50 neuropeptide genes can be present in a single species, and thus neuropeptidergic systems are attractive targets for the development of environmentally friendly pesticides. Such approaches require not only knowledge of the neuropeptidomes of pests, but also detailed knowledge of the corresponding systems in beneficial insects. In Coleoptera, there is no profound knowledge of the neuropeptides in the adephagan lineage, which contains many of the ecologically important predators of caterpillars. We analyzed by transcriptomics, mass spectrometry and immunohistochemistry the neuropeptidomes of the two Carabus species C. violaceus and C. problematicus. This information, which contains detailed data on the differential processing of CAPA peptides, allows for the recognition of features typical only of the polyphagan lineage with its many pests. The neuropeptidomics data, which also confirmed the processing of a number of protein hormones, represent the highest number of neuropeptides that have been identified so far from Coleoptera. The sequences of the mature neuropeptides of the two Carabus species, whose ancestors separated about 13 Mya, are highly similar and no sequence substitutions were found in single-copy neuropeptides.

Analysis of Single Neurons by Perforated Patch Clamp Recordings and MALDI-TOF Mass Spectrometry

Single-cell mass spectrometry has become an established technique to study specific molecular properties such as the neuropeptide complement of identified neurons. Here, we describe a strategy to characterize, by MALDI-TOF mass spectrometry, neurochemical composition of neurons that were identified by their electrophysiological and neuroanatomical characteristics. The workflow for the first time combined perforated patch clamp recordings with dye loading by electroporation for electrophysiological and neuroanatomical characterization as well as chemical profiling of somata by MALDI-TOF mass spectrometry with subsequent immunohistochemistry. To develop our protocol, we used identified central olfactory neurons from the American cockroach Periplaneta americana. First, the combined approach was optimized using a relative homogeneous, well-characterized neuron population of uniglomerular projection neurons, which show acetylcholine esterase immunoreactivity. The general applicability of this approach was verified on local interneurons, which are a diverse neuron population expressing highly differentiated neuropeptidomes. Thus, this study shows that the newly established protocol is suitable to comprehensively analyze electrophysiological, neuroanatomical, and molecular properties of single neurons. We consider this approach an important step to foster single-cell analysis in a wide variety of neuron types.

Different processing of CAPA and pyrokinin precursors in the giant mealworm beetle Zophobas atratus (Tenebrionidae) and the boll weevil Anthonomus grandis grandis (Curculionidae)

Capa and pyrokinin (pk) genes in hexapods share a common evolutionary origin. Using transcriptomics and peptidomics, we analyzed products of these genes in two beetles, the giant mealworm beetle (Zophobas atratus; Tenebrionidae) and the boll weevil (Anthonomus grandis grandis; Curculionidae). Our data revealed that even within Coleoptera, which represents a very well-defined group of insects, highly different evolutionary developments occurred in the neuropeptidergic system. These differences, however, primarily affect the general structure of the precursors and differential processing of mature peptides and, to a lesser degree, the sequences of the active core motifs. With the differential processing of the CAPA-precursor in Z. atratus we found a perfect example of completely different products cleaved from a single neuropeptide precursor in different cells. The CAPA precursor in abdominal ganglia of this species yields primarily periviscerokinins (PVKs) whereas processing of the same precursor in neurosecretory cells of the subesophageal ganglion results in CAPA-tryptoPK and a novel CAPA-PK. Particularly important was the detection of that CAPA-PK which has never been observed in the CNS of insects before. The three different types of CAPA peptides (CAPA-tryptoPK, CAPA-PK, PVK) each represent potential ligands which activate different receptors. In contrast to the processing of the CAPA precursor from Z. atratus, no indications of a differential processing of the CAPA precursor were found in A. g. grandis. These data suggest that rapid evolutionary changes regarding the processing of CAPA precursors were still going on when the different beetle lineages diverged. The sequence of the single known PVK of A. g. grandis occupies a special position within the known PVKs of insects and might serve asa basis to develop lineage-specific peptidomimetics capable of disrupting physiological processes regulated by PVKs.

Single Cell Peptidomics: Approach for Peptide Identification by N-Terminal Peptide Derivatization

In recent years, single cell microanalysis techniques have moved into the center stage to study fundamental intracellular interactions and cell-cell communication events, and have led to a better understanding of physiological processes and behavioral patterns. The availability of more sensitive, robust, and precise mass spectrometers improved the detection and characterization of putative neuroactive substances from individual cells. For sequence characterization, particularly when working with samples as small as a single cell, the most crucial step to obtain usable data is sample preparation. For some studies, genetic or molecular data are not available to confirm an amino acid sequence of a putative neuropeptide, and it is necessary to sequence the peptide from the mass spectrometry analysis alone (i.e., de novo sequencing). In this chapter, a protocol is described for de novo sequencing of neuropeptides from individual single cells by N-terminal derivatization using 4-sulfophenyl isothiocyanate and subsequent mass spectrometric analysis.

Identification of mature peptides from pban and capa genes of the moths Heliothis peltigera and Spodoptera littoralis

By transcriptome analysis, we identified PBAN and CAPA precursors in the moths Spodoptera littoralis and Heliothis peltigera which are among the most damaging pests of agriculture in tropical and subtropical Africa as well as in Mediterranean countries. A combination of mass spectrometry and immunocytochemistry was used to identify mature peptides processed from these precursors and to reveal their spatial distribution in the CNS. We found that the sites of expression of pban genes, the structure of PBAN precursors and the processed neuropeptides are very similar in noctuid moths. The sequence of the diapause hormone (DH; tryptopyrokinin following the signal peptide), however, contains two N-terminal amino acids more than expected from comparison with already published sequences of related species. Capa genes of S. littoralis and H. peltigera encode, in addition to periviscerokinins, a tryptopyrokinin showing sequence similarity with DH, which is the tryptopyrokinin of the pban gene. CAPA peptides, which were not known from any noctuid moth so far, are produced in cells of abdominal ganglia. The shape of the release sites of these hormones in H. peltigera represents an exceptionally derived trait state and does not resemble the well-structured abdominal perisympathetic organs which are known from many other insects. Instead, axons of CAPA cells extensively ramify within the ventral diaphragm. The novel information regarding the sequences of all mature peptides derived from pban and capa genes of H. peltigera and S. littoralis now enables a detailed analysis of the bioactivity and species-specificity of the native peptides, especially those from the hitherto unknown capa genes, and to explore their interactions with PBAN/DH receptors.

Evolution of neuropeptides in non-pterygote hexapods

Background

Neuropeptides are key players in information transfer and act as important regulators of development, growth, metabolism, and reproduction within multi-cellular animal organisms (Metazoa). These short protein-like substances show a high degree of structural variability and are recognized as the most diverse group of messenger molecules. We used transcriptome sequences from the 1KITE (1K Insect Transcriptome Evolution) project to search for neuropeptide coding sequences in 24 species from the non-pterygote hexapod lineages Protura (coneheads), Collembola (springtails), Diplura (two-pronged bristletails), Archaeognatha (jumping bristletails), and Zygentoma (silverfish and firebrats), which are often referred to as “basal” hexapods. Phylogenetically, Protura, Collembola, Diplura, and Archaeognatha are currently placed between Remipedia and Pterygota (winged insects); Zygentoma is the sistergroup of Pterygota. The Remipedia are assumed to be among the closest relatives of all hexapods and belong to the crustaceans.

Results

We identified neuropeptide precursor sequences within whole-body transcriptome data from these five hexapod groups and complemented this dataset with homologous sequences from three crustaceans (including Daphnia pulex), three myriapods, and the fruit fly Drosophila melanogaster. Our results indicate that the reported loss of several neuropeptide genes in a number of winged insects, particularly holometabolous insects, is a trend that has occurred within Pterygota. The neuropeptide precursor sequences of the non-pterygote hexapods show numerous amino acid substitutions, gene duplications, variants following alternative splicing, and numbers of paracopies. Nevertheless, most of these features fall within the range of variation known from pterygote insects. However, the capa/pyrokinin genes of non-pterygote hexapods provide an interesting example of rapid evolution, including duplication of a neuropeptide gene encoding different ligands.

Conclusions

Our findings delineate a basic pattern of neuropeptide sequences that existed before lineage-specific developments occurred during the evolution of pterygote insects.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-016-0621-4) contains supplementary material, which is available to authorized users.

Identification and expression of capa gene in the fire ant, Solenopsis invicta

Recent genome analyses suggested the absence of a number of neuropeptide genes in ants. One of the apparently missing genes was the capa gene. Capa gene expression in insects is typically associated with the neuroendocrine system of abdominal ganglia; mature CAPA peptides are known to regulate diuresis and visceral muscle contraction. The apparent absence of the capa gene raised questions about possible compensation of these functions. In this study, we re-examined this controversial issue and searched for a potentially unrecognized capa gene in the fire ant, Solenopsis invicta. We employed a combination of data mining and a traditional PCR-based strategy using degenerate primers designed from conserved amino acid sequences of insect capa genes. Our findings demonstrate that ants possess and express a capa gene. As shown by MALDI-TOF mass spectrometry, processed products of the S. invicta capa gene include three CAPA periviscerokinins and low amounts of a pyrokinin which does not have the C-terminal WFGPRLa motif typical of CAPA pyrokinins in other insects. The capa gene was found with two alternative transcripts in the CNS. Within the ventral nerve cord, two capa neurons were immunostained in abdominal neuromeres 2–5, respectively, and projected into ventrally located abdominal perisympathetic organs (PSOs), which are the major hormone release sites of abdominal ganglia. The ventral location of these PSOs is a characteristic feature and was also found in another ant, Atta sexdens.