Evidence from multiple gene sequences indicates that termites evolved from wood-feeding cockroaches

Transport of African swine fever virus from assembly sites to the plasma membrane is dependent on microtubules and conventional kinesin

African swine fever virus (ASFV) is a large DNA virus that assembles in perinuclear viral factories located close to the microtubule organizing center. In this study, we have investigated the mechanism by which ASFV reaches the cell surface from the site of assembly. Immunofluorescence microscopy revealed that at 16 h postinfection, mature virions were aligned along microtubules. Furthermore, virus movement to the cell periphery was inhibited when microtubules were depolymerized by nocodazole. In addition, ASFV infection resulted in the increased acetylation of microtubules as well as their protection against depolymerization by nocodazole. Immunofluorescence microscopy showed that conventional kinesin was recruited to virus factories and to a large fraction of virus particles in the cytoplasm. Consistent with a role for conventional kinesin during ASFV egress to the cell periphery, overexpression of the cargo-binding domain of the kinesin light chain severely inhibited the movement of particles to the plasma membrane. Based on our observations, we propose that ASFV is recognized as cargo by conventional kinesin and uses this plus-end microtubule motor to move from perinuclear assembly sites to the plasma membrane.

Characterization of termite lipophorin and its involvement in hydrocarbon transport

The transport of lipids constitutes a vital function in insects and requires the plasma lipoprotein lipophorin. In all insects examined to date, cuticular hydrocarbons are also transported through the hemolymph by lipophorin, and in social insects they play important roles not only in water proofing the cuticle but also in nestmate recognition. High-density lipophorin (HDLp), isolated from Reticulitermes flavipes plasma by KBr gradient ultracentrifugation, contains 66.2% protein and 33.8% lipids; hydrocarbons constitute its major neutral lipid (20.4% of total lipids). Anti-lipophorin serum was generated in rabbit and its specific association with lipophorin, and not with any other plasma proteins, was verified with Western blotting. Immunoprecipitation also confirmed that this antibody specifically recognizes lipophorin, because all hemolymph hydrocarbons of the termites R. flavipes and R. lucifugus and the cockroach Supella longipalpa, which associate only with lipophorin, were recovered in the immunoprecipitated protein. Cross-reactivity of the antiserum with lipophorin from related species was investigated by double immunodiffusion with 10 termite species in the genera Reticulitermes, Coptotermes, Zootermopsis, and Kalotermes, and with five cockroach species. Involvement of lipophorin in hydrocarbon transport was shown by injecting HDLp antiserum into Zootermopsis nevadensis and then monitoring the de novo biosynthesis of hydrocarbons and their transport to the cuticular surface; the antiserum significantly disrupted hydrocarbon transport. ELISA revealed a gradual increase in the lipophorin titer in successively larger R. flavipes workers, and differences among castes in lipophorin titers were highest between nymphs and first instar larvae.

Aligned 18S and Insect Phylogeny

The nuclear small subunit rRNA (18S) has played a dominant role in the estimation of relationships among insect orders from molecular data. In previous studies, 18S sequences have been aligned by unadjusted automated approaches (computer alignments that are not manually readjusted), most recently with direct optimization (simultaneous alignment and tree building using a program called "POY"). Parsimony has been the principal optimality criterion. Given the problems associated with the alignment of rRNA, and the recent availability of the doublet model for the analysis of covarying sites using Bayesian MCMC analysis, a different approach is called for in the analysis of these data. In this paper, nucleotide sequence data from the 18S small subunit rRNA gene of insects are aligned manually with reference to secondary structure, and analyzed under Bayesian phylogenetic methods with both GTR+I+G and doublet models in MrBayes. A credible phylogeny of Insecta is recovered that is independent of the morphological data and (unlike many other analyses of 18S in insects) not contradictory to traditional ideas of insect ordinal relationships based on morphology. Hexapoda, including Collembola, are monophyletic. Paraneoptera are the sister taxon to a monophyletic Holometabola but weakly supported. Ephemeroptera are supported as the sister taxon of Neoptera, and this result is interpreted with respect to the evolution of direct sperm transfer and the evolution of flight. Many other relationships are well-supported but several taxa remain problematic, e.g., there is virtually no support for relationships among orthopteroid orders. A website is made available that provides aligned 18S data in formats that include structural symbols and Nexus formats.

Molecular phylogeny of Asian termites (Isoptera) of the families Termitidae and Rhinotermitidae based on mitochondrial COII sequences

The families Termitidae and Rhinotermitidae are the most evolved and diverse groups of the social insects, termites (Order Isoptera), showing elaborated morphology and complex behavior. Molecular phylogeny of termites with the emphasis on these families was examined by Bayesian and maximum-likelihood analyses based on DNA sequence of mitochondrial cytochrome oxidase II (COII) gene of 31 genera sampled in Asia (mainly Thailand and Japan) along with those reported previously. Termitidae was monophyletic and originated from within polyphyletic Rhinotermitidae. Among the four subfamilies of Termitidae, Macrotermitinae was monophyletic suggesting a single common origin of fungus-growing habit characteristic for this subfamily, and was placed in the basal position in the family. A group consisting of other subfamilies Termitinae and Nasutitermitinae, though some important groups were still untouched, was the most apical but neither Termitinae nor Nasutitermitinae formed a monophyletic lineage. It was implied that, as defense systems of the soldier castes, the appearance of snapping mandibles has occurred at a single event, but the development of nasus for chemical secretion has probably not. Our tree provides some evidence concerning contradictions in the previously proposed phylogeny of termites.

Molecular phylogeny and biogeography of the Korean woodroaches Cryptocercus spp

Phylogenetic relationships and biogeography of Northeast Asian Cryptocercus were inferred based on the DNA sequences of mitochondrial COII and 16S rRNA genes and nuclear 18S rRNA gene. The results suggest that two clades exist in Korean populations. The southwestern population (Cryptocercus from Jiri-san) was more closely related to the populations from Northeast China and eastern Russia than to all the other Korean Cryptocercus. According to molecular-based estimated divergence times, the divergence event occurred between Cryptocercus in Jiri-san, Northeast China and eastern Russia and those in the remaining South Korea during the Miocene (7.5-17.4Myr ago), and then the divergence event between Cryptocercus in Jiri-san and those in Northeast China and eastern Russia occurred 0.8-1.9Myr ago. In the Korean Peninsula, Jiri-san is located in the most southwestern region among the high mountains surveyed. The location is the farthest from Northeast China and eastern Russia among sampling localities in South Korea. Thus, it was unexpected that the southwestern populations are more closely related to those from Northeast China and eastern Russia rather than to the other Korean Cryptocercus. Based on Korean topography and estimated divergence times, possible scenarios are proposed for the current geographical distribution of Korean Cryptocercus.

Action pattern, specificity, lytic activities, and physiological role of five digestive beta-glucanases isolated from Periplaneta americana

Three laminarinases (LAM, LIC 1, and LIC 2) and two cellulases (CEL 1 and CEL 2) were purified to homogeneity from Periplaneta americana midguts. These beta-glucanases are secreted by salivary glands, stabilized by calcium ions, and have pH optima around 6. LAM (46 kDa) is active only on laminarin, native or with oxidized ends, and so it is an endo-beta-1,3-glucanase (EC 3.2.1.39). It processively releases mainly glucose from laminarin and shows lytic activity on fungal cells. LIC 1 (25 kDa) is an endo-beta-1,3(4)-glucanase (EC 3.2.1.6.), because it cleaves internal bonds on both laminarin and lichenin. LIC 1 lyses fungal cells and apparently have high affinity for sequences of cellotetraoses linked by beta-1,3 links, releasing cellotetraose from lichenin. The reaction catalyzed by LIC 1 is not in rapid equilibrium, as suggested by activity-pH data. These data also showed that a group in LIC 1 with pK=4.9 is necessary for substrate binding. LIC 2 (23 kDa) seems to be similar to LIC 1. The laminarinases are inactivated by carbodiimide, suggesting the presence of a carboxyl group involved in catalysis. LAM and LIC 2 are inhibited by excess laminarin as substrate. CEL 1 (72 kDa) and CEL 2 (73 kDa) quickly decrease the molecular weight of lichenin used as substrate. Therefore, they are endo-beta-1,4-glucanases (EC 3.2.1.4). Both CEL 1 and CEL 2 are also active on crystalline cellulose. The specificities of P. americana beta-glucanases agree with the omnivorous detritus-feeding habit of this insect, as they are able to attack plant (CEL 1, CEL 2, LIC 1 and LIC 2) and fungal (LIC 1 and LAM) cell walls.

Evidence for the presence of a cellulase gene in the last common ancestor of bilaterian animals

Until recently, the textbook view of cellulose hydrolysis in animals was that gut-resident symbiotic organisms such as bacteria or unicellular eukaryotes are responsible for the cellulases produced. This view has been challenged by the characterization and sequencing of endogenous cellulase genes from some invertebrate animals, including plant-parasitic nematodes, arthropods and a mollusc. Most of these genes are completely unrelated in terms of sequence, and their evolutionary origins remain unclear. In the case of plant-parasitic nematodes, it has been suggested that their ancestor obtained a cellulase gene via horizontal gene transfer from a prokaryote, and similar suggestions have been made about a cellulase gene recently discovered in a sea squirt. To improve understanding about the evolution of animal cellulases, we searched for all known types of these enzymes in GenBank, and performed phylogenetic comparisons. Low phylogenetic resolution was found among most of the sequences examined, however, positional identity in the introns of cellulase genes from a termite, a sea squirt and an abalone provided compelling evidence that a similar gene was present in the last common ancestor of protostomes and deuterostomes. In a different enzyme family, cellulases from beetles and plant-parasitic nematodes were found to cluster together. This result questions the idea of lateral gene transfer into the ancestors of the latter, although statistical tests did not allow this possibility to be ruled out. Overall, our results suggest that at least one family of endogenous cellulases may be more widespread in animals than previously thought.

The evolution of soil-burrowing cockroaches (Blattaria: Blaberidae) from wood-burrowing ancestors following an invasion of the latter from Asia into Australia

Morphologically similar cockroaches in the subfamilies Panesthiinae and Geoscapheinae (Blattaria: Blaberidae) display contrasting feeding habits, behaviour and biogeographical distributions. Panesthiinae, found throughout Asia and Australia, all live in and feed on decaying wood that they burrow into. Geoscapheinae are restricted to Australia and construct and live in burrows in the soil, where they feed on dry leaves taken from the surface. A lack of knowledge about phylogenetic relationships among these cockroaches hinders an understanding of the factors that have shaped the evolution of their diverse lifestyles and biogeography. To address this issue, we sequenced three genes from representatives of nine of the 10 genera in the two subfamilies, and performed phylogenetic analyses. The well-supported topology revealed the Panesthiinae to be paraphyletic with respect to the Geoscapheinae. Soil-burrowing cockroaches appear to have evolved from a lineage of wood burrowers that invaded Australia from the north some time after the merging of the Asian and Australian tectonic plates ca. 20 Myr ago. The main factor promoting the evolution of soil burrowing is likely to have been one of the periods of strong aridity that Australia has experienced since the Miocene period.

Termite symbiotic systems: efficient bio-recycling of lignocellulose

Termites thrive in great abundance in terrestrial ecosystems and play important roles in biorecycling of lignocellulose. Together with their microbial symbionts, they efficiently decompose lignocellulose. In so-called lower termites, a dual decomposing system, consisting of the termite's own cellulases and those of its gut protists, was elucidated at the molecular level. Higher termites degrade cellulose apparently using only their own enzymes, because of the absence of symbiotic protists. Termite gut prokaryotes efficiently support lignocellulose degradation. However, culture-independent molecular studies have revealed that the majority of these gut symbionts have not yet been cultivated, and that the gut symbiotic community shows a highly structured spatial organization. In situ localization of individual populations and their functional interactions are important to understand the nature of symbioses in the gut. In contrast to cellulose, lignin degradation does not appear to be important in the gut of wood-feeding termites. Soil-feeding termites decompose humic substances in soil at least partly, but little is known about the decomposition. Fungus-growing termites are successful in the almost complete decomposition of lignocellulose in a sophisticated cooperation with basidiomycete fungi cultivated in their nest. A detailed understanding of efficient biorecycling systems, such as that for lignocellulose, and the symbioses that provide this efficiency will benefit applied microbiology and biotechnology.

A unique mushroom body substructure common to basal cockroaches and to termites

The mushroom bodies of the cockroach Periplaneta americana are made up of intrinsic neurons (class I and class II Kenyon cells) with dendrites in a dorsal calyx and axons that bifurcate into medial and vertical lobes. Here, we describe a substructure of the cockroach mushroom bodies composed of a previously unrecognized class of Kenyon cells with distinct morphologies. The embryonically produced class III Kenyon cells form a separate accessory calyx below the calyx proper. The medial branches of class III Kenyon cell axons form the previously described "gamma bulb," whereas the vertical branches leave the vertical lobe to form a toroidal "lobelet" around the posterior surface. Taking advantage of the morphologically and immunochemically distinct nature of the lobelet, we have attempted to determine the distribution of this unique structure in other insects of the taxon Dictyoptera (cockroaches, mantises, and termites). Our data indicate that the lobelet is present only in basal cockroaches and in termites, supporting existing theories of a close phylogenetic relationship between these groups. Higher termites possess a duplicated lobe structure due to immense elaboration of the processes of class III Kenyon cells. The degree of complexity in the mushroom body lobes of termites agrees with current taxonomic arrangements of the Isoptera based on non-neural morphological and DNA sequence analyses. It thus appears that the evolution of the Dictyoptera has been accompanied by increasing complexity of the mushroom bodies, achieved in part through the further specialization and elaboration of a subset of Kenyon cells.

The draft genome of Ciona intestinalis: insights into chordate and vertebrate origins

The first chordates appear in the fossil record at the time of the Cambrian explosion, nearly 550 million years ago. The modern ascidian tadpole represents a plausible approximation to these ancestral chordates. To illuminate the origins of chordate and vertebrates, we generated a draft of the protein-coding portion of the genome of the most studied ascidian, Ciona intestinalis. The Ciona genome contains approximately 16,000 protein-coding genes, similar to the number in other invertebrates, but only half that found in vertebrates. Vertebrate gene families are typically found in simplified form in Ciona, suggesting that ascidians contain the basic ancestral complement of genes involved in cell signaling and development. The ascidian genome has also acquired a number of lineage-specific innovations, including a group of genes engaged in cellulose metabolism that are related to those in bacteria and fungi.

Molecular cloning of lysozyme-encoding cDNAs expressed in the salivary gland of a wood-feeding termite, Reticulitermes speratus

Two kinds of PCR-product cDNAs that encode premature lysozyme peptides (Rs-Lys1 and Rs-Lys2) were cloned from workers of a Japanese damp-wood termite, Reticulitermes speratus. The Rs-Lys1 and Rs-Lys2 cDNAs encoded deduced sequences of 170 and 164 amino acids, respectively. Alignment of these sequences with those of other insect lysozymes showed that the cDNAs encode lysozyme homologues with putative signal peptides, insertions eight amino acids long, and a relatively long C-terminus (13-17 amino acids). A maximum likelihood tree, constructed using the cDNA sequences, indicated that the termite lysozymes are related to those of mosquitoes and lepidopterans. Southern-blotting analysis identified single copies of these lysozyme genes in the termite. Reverse transcript (RT)-PCR and in situ hybridization experiments showed that Rs-Lys1 and Rs-Lys2 are expressed in the salivary glands of worker termites. Here, we discuss the possible digestive function of these lysozymes.

A digestive beta-glucosidase from the salivary glands of the termite, Neotermes koshunensis (Shiraki): distribution, characterization and isolation of its precursor cDNA by 5'- and 3'-RACE amplifications with degenerate primers

beta-Glucosidase activity [EC 3.2.1.21] was measured in the salivary glands and the gut of wood-eating termite, Neotermes koshunensis (Shiraki). 75% of the activity was detected in the salivary glands, whereas 15% of the activity was present in the hindgut, where numerous symbiotic flagellates reside. The salivary beta-glucosidase was partially purified by ion-exchange and gel filtration chromatography. The molecular weight of the salivary beta-glucosidase was 60 kDa, and the K(m) value on cellobiose was 2.5 mM. Its optimal pH was 5.6 and the activity was stable from 20 degrees C up to 45 degrees C. In addition to cellobiose, p-nitrophenyl-beta-D-fucopyranoside and laminaribiose were efficiently hydrolyzed by the salivary beta-glucosidase. Degenerate PCR using primers designed from N-terminal amino acid sequences of the salivary beta-glucosidase resulted in a cDNA fragment of 1730 bp, encoding 498 amino acids and with sequence similarity to glycosyl hydrolase family 1. Reverse-transcription (RT)-PCR showed that this beta-glucosidase is produced only in the salivary glands.

Evolution and phylogenetic information content of the ribosomal DNA repeat unit in the Blattodea (Insecta)

The organization, structure, and nucleotide variability of the ribosomal repeat unit was compared among families, genera, and species of cockroaches (Insecta:Blattodea). Sequence comparisons and molecular phylogenetic analyses were used to describe rDNA repeat unit variation at differing taxonomic levels. A reverse similar 1200 bp fragment of the 28S rDNA sequence was assessed for its potential utility in reconstructing higher-level phylogenetic relationships in cockroaches. Parsimony and maximum likelihood analyses of these data strongly support the expected pattern of relationships among cockroach groups. The examined 5' end of the 28S rDNA is shown to be an informative marker for larger studies of cockroach phylogeny. Comparative analysis of the nucleotide sequences of the rDNA internal transcribed spacers (ITS1 and ITS2) among closely related species of Blattella and Periplaneta reveals that ITS sequences can vary widely in primary sequence, length, and folding pattern. Secondary structure estimates for the ITS region of Blattella species indicate that variation in this spacer region can also influence the folding pattern of the 5.8S subunit. These results support the idea that ITS sequences play an important role in the stability and function of the rRNA cluster.

Dual cellulose-digesting system of the wood-feeding termite, Coptotermes formosanus Shiraki

The distribution of endo-beta-1,4-glucanase (EG) components in the digestive system of the wood-feeding termite, Coptotermes formosanus Shiraki, was investigated by zymogram analysis using polyacrylamide gel electrophoresis, followed by N-terminal protein sequencing. EG components similar to glycoside hydrolase family (GHF) 9 members were restricted to the salivary glands, the foregut, and the midgut, whereas components similar to GHF7 members were confined to the hindgut where numerous cellulolytic flagellates were harbored. RT-PCR experiments revealed that five GHF9 EG mRNAs (1348 bp) homologous to other termite EGs were expressed in the salivary glands and the midgut. The crude extract prepared from the midgut as well as that from the hindgut produced glucose from crystalline cellulose. These data suggest that C. formosanus has two independent cellulose-digesting systems: one in the midgut where cellulose digestion is accomplished by endogenous cellulases and the other in the hindgut which makes use of other cellulases possibly from symbiotic flagellates.

Comparative social biology of basal taxa of ants and termites

Lacking a comprehensive fossil record, solitary representatives of the taxa, and/or a definitive phylogeny of closely related insects, comparison of the life history and social biology of basal, living groups is one of the few available options for developing inferences regarding the early eusocial evolution of ants and termites. Comparisons of a select group of basal formicid and isopteran taxa suggest that the reproductive organization of colonies and their patterns of division of labor were particularly influenced, in both groups, by nesting and feeding ecology. Opportunities for serial inheritance of the nest structure and colony population by kin may have been significant in the evolution of multiple reproductive forms and options. Disease has been a significant factor in the evolution of social organization in ants and termites, but the adaptive mechanisms of infection control differ. Evaluations of the convergent and divergent social biology of the two taxa can generate novel domains of research and testable hypotheses.

Cleavage of the xylosyl serine linkage between a core peptide and a glycosaminoglycan chain by cellulases

We previously found that endo-beta-xylosidase from Patinopecten is an endo-type glycosidase that cleaves the xylosyl serine linkage between a glycosaminoglycan chain and its core protein (Takagaki, K., Kon, A., Kawasaki, H., Nakamura, T., Tamura, S., and Endo, M. (1990) J. Biol. Chem. 265, 854-860). Screening for endo-beta-xylosidase activity in several cellulases detected this activity in the enzymes from Aspergillus niger, Penicillium funiculosum, Trichoderma reesei, Trichoderma viride, and Irpex lacteus. The cellulase derived from A. niger was purified, and its molecular weight was determined to be 26,000 by SDS-PAGE. Examination of the specificity of the cellulase revealed that 1) the enzyme acts on the linkage region (xylosyl serine) between a core peptide and a glycosaminoglycan chain; 2) enzymatic activity is greater with shorter glycosaminoglycan chains; 3) the enzyme readily hydrolyzes the linkage in glycosaminoglycan peptides, but intact proteoglycan is cleaved only slowly; and 4) the activity is unaffected by the glycosaminoglycan component (chondroitin sulfate, dermatan sulfate, and heparan sulfate). Judging from these enzymatic characteristics, this cellulase is different from the endo-beta-xylosidase of Patinopecten. We believe that this cellulase will become a useful tool in the further development of glycotechnology, because, like the endo-beta-xylosidase of Patinopecten, it enables the release of intact glycosaminoglycans from glycosaminoglycan peptides.

An insect molecular clock dates the origin of the insects and accords with palaeontological and biogeographic landmarks

A unified understanding of >390 Myr of insect evolution requires insight into their origin. Molecular clocks are widely applied for evolutionary dating, but clocks for the class Insecta have remained elusive. We now define a robust nucleotide and amino acid mitochondrial molecular clock encompassing five insect orders, including the Blattaria (cockroaches), Orthoptera (crickets and locusts), Hemiptera (true bugs), Diptera, and Lepidoptera (butterflies and moths). Calibration of the clock using one of the earliest, most extensive fossil records for insects (the early ancestors of extant Blattaria) was congruent with all available insect fossils, with biogeographic history, with the Cambrian explosion, and with independent dating estimates from Lepidopteran families. In addition, dates obtained from both nucleotide and amino acid clocks were congruent with each other. Of particular interest to vector biology is the early date of the emergence of triatomine bugs (99.8-93.5 MYA), coincident with the formation of the South American continent during the breakup of Gondwanaland. More generally, we reveal the insects arising from a common ancestor with the Anostraca (fairy shrimps) at around the Silurian-Ordovician boundary (434.2-421.1 MYA) coinciding with the earliest plant megafossil. We explore Tilyard's theory proposing that the terrestrial transition of the aquatic arthropod ancestor to the insects is associated with a particular plant group (early vascular plants). The major output of the study is a comprehensive series of dates for deep-branching points within insect evolution that can act as calibration points for further dating studies within insect families and genera.

Spirochete and protist symbionts of a termite (Mastotermes electrodominicus) in Miocene amber

Extraordinary preservation in amber of the Miocene termite Mastotermes electrodominicus has led to the discovery of fossil symbiotic microbes. Spirochete bacteria and wood-digesting protists were identified in the intestinal tissue of the insect. Fossil wood (xylem: developing vessel-element cells, fibers, pit connections), protists (most likely xylophagic amitochondriates), an endospore (probably of the filamentous intestinal bacterium Arthromitus = Bacillus), and large spirochetes were seen in thin section by light and transmission electron microscopy. The intestinal microbiota of the living termite Mastotermes darwiniensis, a genus now restricted to northern Australia, markedly resembles that preserved in amber. This is a direct observation of a 20-million-year-old xylophagus termite fossil microbial community.

A new and independently evolved case of xylophagy and the presence of intestinal flagellates in the cockroach Parasphaeria boleiriana (Dictyoptera, Blaberidae, Zetoborinae) from the remnants of the Brazilian Atlantic forest

Parasphaeria boleiriana is a new example of a xylophagous and subsocial cockroach with intestinal flagellates, which was observed in remnants of the Brazilian semideciduous Atlantic forest. Parasphaeria boleiriana formed galleries by burrowing into the rotten trunks of softwood trees in the forest understory. Females stayed in chambers in the wood with their neonate nymphs for 12.4 ± 6.2 days (mean ± SD), but trophallaxis was not yet observed. According to multiseasonal sampling, nymphal development took longer than 1 year, but adults appeared to be short-lived. Nymphs did not disperse within the trunk during their development but remained relatively aggregated. Parasphaeria boleiriana fed on wood, and their digestive tract harboured five species of flagellates belonging to the order Trichomonadida. All these characteristics contrast with those of other known wood-feeding cockroaches, especially the low adult longevity and short period of brood care, associated with a high prevalence of intestinal flagellates.