Comparative genomic analysis of C-type lectin-domain genes in seven holometabolous insect species.

C-type lectins (CTLs) recognize various glycoconjugates through carbohydrate recognition domains (CRDs) and they play important roles in immune responses. In this study, comparative genomic analysis of CTLs were performed in 7 holometabolous species. CTL-S1 to S8 and CTL-X1 to X4 orthologous groups existed in the 7 species, while CTL-X5 group with dual-CRD, CTL-S11 group with triple-CRD, CTL-S9 group with a long C-terminus and Lepidopteran specific CTL-S10 group were not conserved. SliCTL-S12 to S14 cluster was only present in Spodoptera litura, and CTL-S genes were expanded on chromosomes 2 L and 2 R in Drosophila melanogaster. Most IMLs were clustered into three groups and the numbers of IMLs vary among species due to gene duplications. D. melanogaster specific CTLs and Lepidopteran IMLs within each of the three groups evolved more rapidly with higher dN/dS ratios. Two CRDs in IMLs clustered into two clades, with conserved Cys4-Cys5 and Cys1-Cys2 bonds in the first and second CRDs, respectively. The CTL-S and CTL-X family members in S. litura were mainly expressed in the fat body of 5th but not 6th instar larvae, and responded differently to S. litura nucleopolyhedrovirus (SpltNPV) and Nomuraea rileyi infection. The transcription levels of SliCTLs that expressed in fat body but not highly expressed in hemocytes were decreased at the middle and late stages of SpltNPV infection, and the mRNA levels of SliCTLs highly or specifically expressed in hemocytes were mainly decreased by SpltlNPV, N. rileyi and Bacillus thuringiensis infection. These results provide valuable information for further exploration of CTL functions in host-pathogen interaction.

Signatures of DNA Methylation across Insects Suggest Reduced DNA Methylation Levels in Holometabola.

It has been experimentally shown that DNA methylation is involved in the regulation of gene expression and the silencing of transposable element activity in eukaryotes. The variable levels of DNA methylation among different insect species indicate an evolutionarily flexible role of DNA methylation in insects, which due to a lack of comparative data is not yet well-substantiated. Here, we use computational methods to trace signatures of DNA methylation across insects by analyzing transcriptomic and genomic sequence data from all currently recognized insect orders. We conclude that: 1) a functional methylation system relying exclusively on DNA methyltransferase 1 is widespread across insects. 2) DNA methylation has potentially been lost or extremely reduced in species belonging to springtails (Collembola), flies and relatives (Diptera), and twisted-winged parasites (Strepsiptera). 3) Holometabolous insects display signs of reduced DNA methylation levels in protein-coding sequences compared with hemimetabolous insects. 4) Evolutionarily conserved insect genes associated with housekeeping functions tend to display signs of heavier DNA methylation in comparison to the genomic/transcriptomic background. With this comparative study, we provide the much needed basis for experimental and detailed comparative analyses required to gain a deeper understanding on the evolution and function of DNA methylation in insects.

Global map of oxytocin/vasopressin-like neuropeptide signalling in insects.

Oxytocin and vasopressin mediate a range of physiological functions that are important for osmoregulation, reproduction, social behaviour, memory and learning. The origin of this signalling system is thought to date back ~600 million years. Oxytocin/vasopressin-like peptides have been identified in several invertebrate species and they appear to be functionally related across the entire animal kingdom. There is little information available about the biology of this peptide G protein-coupled receptor signalling system in insects. Recently over 200 insect genome/transcriptome datasets were released allowing investigation of the molecular structure and phylogenetic distribution of the insect oxytocin/vasopressin orthologue - inotocin peptides and their receptors. The signalling system is present in early arthropods and representatives of some early-diverging lineages. However, Trichoptera, Lepidoptera, Siphonaptera, Mecoptera and Diptera, lack the presence of inotocin genes, which suggests the peptide-receptor system was probably lost in their common ancestor ~280 million-years-ago. In addition we detected several losses of the inotocin signalling system in Hemiptera (white flies, scale insects and aphids), and the complete absence in spiders (Chelicerata). This unique insight into evolutionarily patterns and sequence diversity of neuroendocrine hormones will provide opportunities to elucidate the physiology of the inotocin signalling system in one of the largest group of animals.

Connecting caddisworm silk structure and mechanical properties: combined infrared spectroscopy and mechanical analysis.

The underwater silk of an aquatic casemaking caddisfly larvae (Hesperophylax occidentalis) is viscoelastic, and displays distinct yield behaviour, large strain cycle hysteresis and near complete recovery of its initial strength and stiffness when unloaded. Yield followed by a stress plateau has been attributed to sequential rupture of serial Ca(2+)-cross-linked phosphoserine (pS) ß-domains. Spontaneous recovery has been attributed to refolding of the Ca(2+)/pS domains powered by an elastic network. In this study, native Ca(2+) ions were exchanged with other metal ions, followed by combined mechanical and FTIR analysis to probe the contribution of pS/metal ion complexes to silk mechanical properties. After exchange of Ca(2+) with Na(+), the fibres are soft elastomers and the infrared spectra are consistent with Cv3 symmetry of the -[Formula: see text] groups. Multivalent metal ions decreased the -[Formula: see text] symmetry and the symmetric stretching modes (vs) split in a manner characteristic of ordered phosphate compounds, such as phosphate minerals and lamellar bilayers of phosphatidic acid lipids. Integrated intensities of the vs bands, indicative of the metal ion's effect on transition dipole moment of the P-O bonds, and thereby the strength of the phosphate metal complex, increased in the order: Na(+) < Mg(2+) < Sr(2+) < Ba(2+) < Ca(2+) < Eu(3+) < La(3+) < Zn(2+) < Fe(2+) With a subset of the metal ion series, the initial stiffness and yield stress of metal ion-exchanged fibres increased in the same order: [Formula: see text] [Formula: see text] establishing the link between phosphate transition dipole moments and silk fibre strength.