Early responses of silkworm midgut to microsporidium infection--A Digital Gene Expression analysis.

Host-pathogen interactions are complex processes, which have been studied extensively in recent years. In insects, the midgut is a vital organ of digestion and nutrient absorption, and also serves as the first physiological and immune barrier against invading pathogenic microorganisms. Our focus is on Nosema bombycis, which is a pathogen of silkworm pebrine and causes great economic losses to the silk industry. A complete understanding of the host response to infection by N. bombycis and the interaction between them is necessary to prevent this disease. Silkworm midgut infected with N. bombycis is a good model to investigate the early host responses to microsporidia infection and the interaction between the silkworm and the microsporidium. Using Digital Gene Expression analysis, we investigated the midgut transcriptome profile of P50 silkworm larvae orally inoculated with N. bombycis. At 6, 12, 18, 24, 48, 72, and 96 h post-infection (hpi), 247, 95, 168, 450, 89, 80, and 773 DEGs were identified, respectively. KEGG pathway analysis showed the influence of N. bombycis infection on many biological processes including folate biosynthesis, spliceosome, nicotinate and nicotinamide metabolism, protein export, protein processing in endoplasmic reticulum, lysosome, biosynthesis of amino acids, ribosome, and RNA degradation. In addition, a number of differentially expressed genes involved in the immune response were identified. Overall, the results of this study provide an understanding of the strategy used by silkworm as a defense against the invasion by N. bombycis. Similar interactions between hosts and pathogens infection may exist in other species.

Identification of sumoylated proteins in the silkworm Bombyx mori.

Small ubiquitin-like modifier (SUMO) modification (SUMOylation) is an important and widely used reversible modification system in eukaryotic cells. It regulates various cell processes, including protein targeting, transcriptional regulation, signal transduction, and cell division. To understand its role in the model lepidoptera insect Bombyx mori, a recombinant baculovirus was constructed to express an enhanced green fluorescent protein (eGFP)-SUMO fusion protein along with ubiquitin carrier protein 9 of Bombyx mori (BmUBC9). SUMOylation substrates from Bombyx mori cells infected with this baculovirus were isolated by immunoprecipitation and identified by LC-ESI-MS/MS. A total of 68 candidate SUMOylated proteins were identified, of which 59 proteins were functionally categorized to gene ontology (GO) terms. Analysis of kyoto encyclopedia of genes and genomes (KEGG) pathways showed that 46 of the identified proteins were involved in 76 pathways that mainly play a role in metabolism, spliceosome and ribosome functions, and in RNA transport. Furthermore, SUMOylation of four candidates (polyubiquitin-C-like isoform X1, 3-hydroxyacyl-CoA dehydrogenase, cyclin-related protein FAM58A-like and GTP-binding nuclear protein Ran) were verified by co-immunoprecipitation in Drosophila schneide 2 cells. In addition, 74% of the identified proteins were predicted to have at least one SUMOylation site. The data presented here shed light on the crucial process of protein sumoylation in Bombyx mori.

Detection of Nosema bombycis by FTA cards and loop-mediated isothermal amplification (LAMP).

We successfully established a detection method which exhibited a markedly higher sensitivity than previously developed detection methods for Nosema bombycis by combining glass beads, FTA card, and LAMP. Spores of N. bombycis were first broken by acid-washed glass beads; the DNA was subsequently extracted and purified with the FTA card, and LAMP was performed using primers (LSU296) designed based on the sequence of the LSU rRNA of N. bombycis. The minimum detection concentration was 10 spores/mL. When this method was used to detect pebrine disease in silkworm egg, the detection rate for 500 silkworm eggs, in which only one egg was infected with N. bombycis, was 100 % under our optimized conditions. If the number of eggs in the sample increased to 800 or 1,000, the sample was divided into two equal portions, and the eggs were smashed with glass beads after the addition of 1 mL of TE buffer. The liquid in two tubes was later mixed and applied to the FTA card, and the detection rates were 100 %. Furthermore, the LAMP method established in our study could detect N. bombycis infection in silkworm 24 h earlier than microscopy.