Characterization of a divergent Sec61beta gene in microsporidia

The development of silk glands and transcriptome aberration induced by cyantraniliprole in Bombyx mori

Bombyx mori is an insect species of great economic importance, and its silk gland is a vital organ for the synthesis and secretion of silk protein. However, long-term artificial domestication of B. mori has resulted in high sensitivity to chemical toxins, especially insecticides. Cyantraniliprole (Cya), a second-generation ryanodine receptor modulator insecticide, is widely utilized in agriculture for pest control. In this study, the impact of Cya toxicity on the development of silk glands in the 5th instar larvae of B. mori was assessed using Cya LC5, LC10 and LC20, as well as a starvation treatment group for comparison. Short-term exposure (24 h) to different concentrations of Cya resulted in delayed development of silk glands in B. mori. Meanwhile, the body weight, silk gland weight, silk gland index and cocoon quality were significantly reduced in a concentration-dependent manner, except for the Cya LC5 treatment. Histopathological and ultrastructural analysis revealed that Cya LC10 induced disruption of the nuclear membrane and endoplasmic reticulum in the posterior silk gland (PSG) cells, leading to the formation of intracellular vacuoles. Transcriptome sequencing of PSGs identified 2152 genes that were differentially expressed after exposure to Cya LC10, with 1153 down-regulated genes and 999 up-regulated genes. All differentially expressed genes were subjected to functional annotation using gene ontology and Kyoto encyclopedia of genes and genomes database, and it was found that protein synthesis-related pathways were significantly enriched, with the majority of genes being down-regulated. Furthermore, the transcription levels of genes involved in "protein processing in endoplasmic reticulum", "protein export", "proteasome" and "DNA replication" were quantified using qRT-PCR. Our findings suggested that short-term exposure to Cya LC10 resulted in disruption of DNA replication, as well as protein transport, processing and hydrolysis in the PSG cells of B. mori. The results of this study provide a theoretical foundation for the safe utilization of Cya in sericulture production.

Proteasome Inhibition Is an Effective Treatment Strategy for Microsporidia Infection in Honey Bees

The microsporidia Nosema ceranae is an obligate intracellular parasite that causes honey bee mortality and contributes to colony collapse. Fumagillin is presently the only pharmacological control for N. ceranae infections in honey bees. Resistance is already emerging, and alternative controls are critically needed. Nosema spp. exhibit increased sensitivity to heat shock, a common proteotoxic stress. Thus, we hypothesized that targeting the Nosema proteasome, the major protease removing misfolded proteins, might be effective against N. ceranae infections in honey bees. Nosema genome analysis and molecular modeling revealed an unexpectedly compact proteasome apparently lacking multiple canonical subunits, but with highly conserved proteolytic active sites expected to be receptive to FDA-approved proteasome inhibitors. Indeed, N. ceranae were strikingly sensitive to pharmacological disruption of proteasome function at doses that were well tolerated by honey bees. Thus, proteasome inhibition is a novel candidate treatment strategy for microsporidia infection in honey bees.

Induction of ER stress, antioxidant and detoxification response by sublethal doses of chlorantraniliprole in the silk gland of silkworm, Bombyx mori

Sublethal doses of chlorantraniliprole (CAP) disrupt spinning disorder in the silkworm Bombyx mori (B. mori) and cause reduced cocoon production. In the present study, we investigated the effects of trace amounts of CAP on morphology and gene expression of the B. mori silk gland, found the posterior silk gland cells were possessed of disintegrated Endoplasmic reticulum (ER), unevenly distributed chromatin after exposure to CAP (0.01 mg/L). Gene expression analysis revealed that IRE1 and ATF6 ER stress-signaling pathways were inhibited, the PERK/CncC pathway was activated. Digital gene expression (DGE) analysis showed that detoxification-related genes, antioxidant genes and genes involved in ER protein processing pathway were expressed differentially in CAP-treated silkworm larvae. Notably, the transcript levels of the detoxification-related genes (CYP4M5, CYP6AB4, GSTD3 and GSTS1) and the antioxidant genes (CAT, TPX and SOD) were significantly increased, and the expression of ER protein processing-related genes (Sec61β, Sec61γ, Sec23α and ERGIC-53) was significantly decreased after CAP exposure. The results showed that sublethal doses of CAP exposure caused ER stress, oxidative damage to the silk gland and the perturbation of protein processing in ER, thereby probably leading to abnormal growth of the silk gland and triggering the spinning failure in silkworm.

From all to (nearly) none: Tracing adaptin evolution in Fungi

The five adaptor protein (AP) complexes function in cargo-selection and coat-recruitment stages of vesicular transport in eukaryotic cells. Much of what we know about AP complex function has come from experimental work using Saccharomyces cerevisiae as a model. Here, using a combination of comparative genomic and phylogenetic approaches we provide evolutionary context for the knowledge gained from this model system by searching the genomes of diverse fungi as well as a member of the sister group to all fungi, Fonticula alba, for presence of AP subunits. First, we demonstrate that F. alba contains all five AP complexes; whereas, similar to S. cerevisiae, most fungi retain only AP-1 to 3. As exceptions, the glomeromycete Rhizophagus irregularis maintains a complete AP-4 and chytrid fungi Spizellomyces punctatus and Batrachochytrium dendrobatidis retain partial AP-4 complexes. The presence of AP-4 subunits in diverse fungi suggests that AP-4 has been independently lost up to seven times in the fungal lineage. In addition to the trend of loss in fungi, we demonstrate that the duplication that gave rise to the β subunits of the AP-1 and AP-2 complexes in S. cerevisiae occurred before the divergence of F. alba and Fungi. Finally, our investigation into the AP complement of basal fungi (Microsporidia and Cryptomycota) demonstrates that while the cryptomycete Rozella allomyces contains an adaptin complement similar to other fungi, the extremely reduced Microsporidia retain, at most, a single cryptic AP complex in the absence of clathrin or any other putative AP-associated coat protein.

Inter-species complementation of the translocon beta subunit requires only its transmembrane domain

In eukaryotes, proteins enter the secretory pathway through the translocon pore of the endoplasmic reticulum. This protein translocation channel is composed of three major subunits, called Sec61alpha, beta and gamma in mammals. Unlike the other subunits, the beta subunit is dispensable for translocation and cell viability in all organisms studied. Intriguingly, the knockout of the Sec61beta encoding genes results in different phenotypes in different species. Nevertheless, the beta subunit shows a high level of sequence homology across species, suggesting the conservation of a biological function that remains ill-defined. To address its cellular roles, we characterized the homolog of Sec61beta in the fission yeast Schizosaccharomyces pombe (Sbh1p). Here, we show that the knockout of sbh1(+) results in severe cold sensitivity, increased sensitivity to cell-wall stress, and reduced protein secretion at 23 degrees C. Sec61beta homologs from Saccharomyces cerevisiae and human complement the knockout of sbh1(+) in S. pombe. As in S. cerevisiae, the transmembrane domain (TMD) of S. pombe Sec61beta is sufficient to complement the phenotypes resulting from the knockout of the entire encoding gene. Remarkably, the TMD of Sec61beta from S. cerevisiae and human also complement the gene knockouts in both yeasts. Together, these observations indicate that the TMD of Sec61beta exerts a cellular function that is conserved across species.

Genome sequence surveys of Brachiola algerae and Edhazardia aedis reveal microsporidia with low gene densities

BACKGROUND

Microsporidia are well known models of extreme nuclear genome reduction and compaction. The smallest microsporidian genomes have received the most attention, but genomes of different species range in size from 2.3 Mb to 19.5 Mb and the nature of the larger genomes remains unknown.

RESULTS

Here we have undertaken genome sequence surveys of two diverse microsporidia, Brachiola algerae and Edhazardia aedis. In both species we find very large intergenic regions, many transposable elements, and a low gene-density, all in contrast to the small, model microsporidian genomes. We also find no recognizable genes that are not also found in other surveyed or sequenced microsporidian genomes.

CONCLUSION

Our results demonstrate that microsporidian genome architecture varies greatly between microsporidia. Much of the genome size difference could be accounted for by non-coding material, such as intergenic spaces and retrotransposons, and this suggests that the forces dictating genome size may vary across the phylum.

Patterns of genome evolution among the microsporidian parasites Encephalitozoon cuniculi, Antonospora locustae and Enterocytozoon bieneusi

Background

Microsporidia are intracellular parasites that are highly-derived relatives of fungi. They have compacted genomes and, despite a high rate of sequence evolution, distantly related species can share high levels of gene order conservation. To date, only two species have been analysed in detail, and data from one of these largely consists of short genomic fragments. It is therefore difficult to determine how conservation has been maintained through microsporidian evolution, and impossible to identify whether certain regions are more prone to genomic stasis.

Principal Findings

Here, we analyse three large fragments of the Enterocytozoon bieneusi genome (in total 429 kbp), a species of medical significance. A total of 296 ORFs were identified, annotated and their context compared with Encephalitozoon cuniculi and Antonospora locustae. Overall, a high degree of conservation was found between all three species, and interestingly the level of conservation was similar in all three pairwise comparisons, despite the fact that A. locustae is more distantly related to E. cuniculi and E. bieneusi than either are to each other.

Conclusions/Significance

Any two genes that are found together in any pair of genomes are more likely to be conserved in the third genome as well, suggesting that a core of genes tends to be conserved across the entire group. The mechanisms of rearrangments identified among microsporidian genomes were consistent with a very slow evolution of their architecture, as opposed to the very rapid sequence evolution reported for these parasites.

A Complete Sec61 Complex in Nosema Bombycis and Its Comparative Genomics Analyses

We characterized a complete Sec61 complex in Nosema bombycis, which has been shown to consist of Sec61alpha, Sec61beta, and Sec61gamma genes. Comparing the genomic regions that harbor the respective subunit genes between N. bombycis, Encephalitozoon cuniculi, and Antonospora locustae, we found that microsporidian genomes have high degree of synteny in short genomic fragment, and that this gene synteny in general might exist throughout microsporidian genomes.