Evolution of Neuropeptide Precursors in Polyneoptera (Insecta)

Comparative analysis of adipokinetic hormones and their receptors in Blattodea reveals novel patterns of gene evolution

Adipokinetic hormone (AKH) is a neuropeptide produced in the insect corpora cardiaca that plays an essential role in mobilising carbohydrates and lipids from the fat body to the haemolymph. AKH acts by binding to a rhodopsin-like G protein-coupled receptor (GPCR), the adipokinetic hormone receptor (AKHR). In this study, we tackle AKH ligand and receptor gene evolution as well as the evolutionary origins of AKH gene paralogues from the order Blattodea (termites and cockroaches). Phylogenetic analyses of AKH precursor sequences point to an ancient AKH gene duplication event in the common ancestor of Blaberoidea, yielding a new group of putative decapeptides. In total, 16 different AKH peptides from 90 species were obtained. Two octapeptides and seven putatively novel decapeptides are predicted for the first time. AKH receptor sequences from 18 species, spanning solitary cockroaches and subsocial wood roaches as well as lower and higher termites, were subsequently acquired using classical molecular methods and in silico approaches employing transcriptomic data. Aligned AKHR open reading frames revealed 7 highly conserved transmembrane regions, a typical arrangement for GPCRs. Phylogenetic analyses based on AKHR sequences support accepted relationships among termite, subsocial (Cryptocercus spp.) and solitary cockroach lineages to a large extent, while putative post-translational modification sites do not greatly differ between solitary and subsocial roaches and social termites. Our study provides important information not only for AKH and AKHR functional research but also for further analyses interested in their development as potential candidates for biorational pest control agents against invasive termites and cockroaches.

Phylogenomics of darkling beetles (Coleoptera: Tenebrionidae) from the Atacama Desert

Background

Tenebrionidae (Insecta: Coleoptera) are a conspicuous component of desert fauna worldwide. In these ecosystems, they are significantly responsible for nutrient cycling and show remarkable morphological and physiological adaptations. Nevertheless, Tenebrionidae colonizing individual deserts have repeatedly emerged from different lineages. The goal of our study was to gain insights into the phylogenetic relationships of the tenebrionid genera from the Atacama Desert and how these taxa are related to the globally distributed Tenebrionidae.

Methods

We used newly generated transcriptome data (47 tribes, 7 of 11 subfamilies) that allowed for a comprehensive phylogenomic analysis of the tenebrionid fauna of this hyperarid desert and fills a gap in our knowledge of the highly diversified Tenebrionidae. We examined two independent data sets known to be suitable for phylogenomic reconstructions. One is based on 35 neuropeptide precursors, the other on 1,742 orthologous genes shared among Coleoptera.

Results

The majority of Atacama genera are placed into three groups, two of which belong to typical South American lineages within the Pimeliinae. While the data support the monophyly of the Physogasterini, Nycteliini and Scotobiini, this does not hold for the Atacama genera of Edrotini, Epitragini, Evaniosomini, Praociini, Stenosini, Thinobatini, and Trilobocarini. A suggested very close relationship of Psammetichus with the Mediterranean Leptoderis also could not be confirmed. We also provide hints regarding the phylogenetic relationships of the Caenocrypticini, which occur both in South America and southern Africa. Apart from the focus on the Tenebrionidae from the Atacama Desert, we found a striking synapomorphy grouping Alleculinae, Blaptinae, Diaperinae, Stenochinae, and several taxa of Tenebrioninae, but not Tenebrio and Tribolium. This character, an insertion in the myosuppressin gene, defines a higher-level monophyletic group within the Tenebrionidae.

Conclusion

Transcriptome data allow a comprehensive phylogenomic analysis of the tenebrionid fauna of the Atacama Desert, which represents one of the seven major endemic tribal areas in the world for Tenebrionidae. Most Atacama genera could be placed in three lineages typical of South America; monophyly is not supported for several tribes based on molecular data, suggesting that a detailed systematic revision of several groups is necessary.

Schistocerca neuropeptides - An update

We compiled a comprehensive list of 67 precursor genes encoding neuropeptides and neuropeptide-like peptides using the Schistocerca gregaria genome and several transcriptome datasets. 11 of these 67 precursor genes have alternative transcripts, bringing the total number of S. gregaria precursors identified in this study to 81. Based on this precursor information, we used different mass spectrometry approaches to identify the putative mature, bioactive peptides processed in the nervous system of S. gregaria. The thereby generated dataset for S. gregaria confirms significant conservation of the entire neuropeptidergic gene set typical of insects and also contains precursors typical of Polyneoptera only. This is in striking contrast to the substantial losses of peptidergic systems in some holometabolous species. The neuropeptidome of S. gregaria, apart from species-specific sequences within the known range of variation, is quite similar to that of Locusta migratoria and even to that of less closely related Polyneoptera. With the S. gregaria peptidomics data presented here, we have thus generated a very useful source of information that could also be relevant for the study of other polyneopteran species.

Biochemically identified neuropeptides in a caddisfly (Trichoptera) and a pygmy mole cricket (Orthoptera: Caelifera: Tridactyloidea)

One representative of the order Trichoptera, namely the caddisfly Chaetopteryx villosa, was investigated along with the pygmy mole cricket Xya capensis which is a representative of the most basal superfamily of the caeliferan Orthoptera, that is, the Tridactyloidea. From both clades neuropeptides have not been biochemically characterized before this study. Here, members of the adipokinetic hormone family (AKHs) are sequenced via liquid chromatography (LC)-ion trap mass spectrometry from methanolic extracts from the corpora cardiaca of respective species. The corpora cardiaca were dissected, methanolic extracts prepared, peptides separated by liquid chromatography (LC), and AKHs detected and sequenced by ion trap mass spectrometry. Both species investigated contain an octapeptide AKH: the trichopteran species has the peptide with the sequence pGlu-Leu-Thr-Phe-Thr-Pro-Ser-Trp amide; the ambiguity of the isobaric amino acids Leu and Ile at position two was solved by comparing retention times on LC and by co-elution with the synthetic Leu² -form. This peptide is known as Aedae-AKH and found in certain dipteran species and in an alderfly (Megaloptera). The tridactyloid species contains the peptide with the sequence pGlu-Val-Asn-Phe-Ser-Pro-Gly-Trp amide which had first been identified in a member of the order Mantophasmatodea and is called Manto-CC. Comparisons are made between the AKH complements of the sister groups Trichoptera and Lepidoptera and their possible relatedness and, on the other hand, between the AKH of X. capensis with those of closely related caeliferan superfamilies. The biology of the two studied species is used to speculate about a possible function of the elucidated hormones. Lastly, the use of a larval stage as starting material for structural neuropeptide information is discussed.

The neuropeptide SMYamide, a SIFamide paralog, is expressed by salivary gland innervating neurons in the American cockroach and likely functions as a hormone

The SMYamide genes are paralogs of the SIFamide genes and code for neuropeptides that are structurally similar to SIFamide. In the American cockroach, Periplanea americana, the SMYamide gene is specifically expressed in the SN2 neurons that innervate the salivary glands and are known to produce action potentials during feeding. The SN2 axon terminals surround rather than directly innervate the salivary gland acini. Therefore one may expect that on activation of these neurons significant amounts of SMYamide will be released into the hemolymph, thus suggesting that SMYamide may also have a hormonal function. In the Periplaneta genome there are two putative SIFamide receptors and these are both expressed not only in the central nervous system and the salivary gland, but also in the gonads and other peripheral tissues. This reinforces the hypothesis that SMYamide also has an endocrine function in this species.