Characterization Of IIM Genes In The Silkworm, Bomby Mori

Peritrophic membrane(PM) is the first defense barrier in the insect peroral infection. It can protect the midgut epithelium from abrasive food particles, being damaged chemical materials, and pathogens infection. It also can compartmentalize digestive processes, allowing for efficient nutrient acquisition and reuse of hydrolytic enzymes. The insect intestinal mucin(IIM) is a major protein constitute of PM. It can maintain the dense microstructure of PM and lubricate digestive tracts. It also has an important role in protecting midgut epithelium from being damaged by ingestd pathogens, physical and chemical injury. Meanwhile, it has attracted a wide spread attention that it is the target of insecticides.The finite researchs about IIMs have contrasted strongly with their importance. Researchs about them have been very limited and it’s hard to isolate, which is due to their complicated structure. At present, all of the known IIMs are obtained by constructing cDNA library construction and antibody screening. However, the genomic data provides a new research angle in this filed.Based on the genomic data, this research identified IIM genes in the silkworm genome, and studied the alternative splicings of IIM genes and the expression of different splicing forms after per os inoculation of BmNPV. RNAi provided experimental proof for of understanding the functions of IIM genes. Not only this study could supply the knowledge for the IIM genes, but also it could offer new ideas for protecting the PM in silkworm. The main results were as follows:1. Identification of IIM genes in the silkwormWe predicted 4 IIM genes in the silkworm genome by bioinformatics method. All of the deduced genes expressed in midgut, which could further confirm the deduced genes were IIM genes.2. Alternative splicing analysis of IIM genes in the silkwormBased on the genomic data and transcriptome data, this research prediced and confirmed that the alternative splicing of BmIIM2 gene and BmIIM4 gene generated 5 and 4 splicing forms, respectively. Nevertherless, there were no splicing forms beween BmⅡM1 gene and BmIIM3 gene. Compared the expression of different splicing forms after per os inoculation of BmNPV, we found that the expression of BmIIM2-5 was not affected by BmNPV infection, but other 8 splicing forms were both affected by BmNPV infection. Both the splicing forms of BmIIM2 gene and BmIIM4 gene might be divided into two types. BmIIM2 gene had both induced expression splicing forms and stable expression splicing forms. BmIIM4 gene had both normal types, which were up-regulated expression at early stage of BmNPV infection and down-regulated expression in the late stage. It also had anomaly types, which were down-regulated expression at early stage of BmNPV infection and up-regulated expression in the late stage. This research showed that different IIM genes and different splicing forms had different roles in resisting to BmNPV.3. The effect on the survival rates by interference IIM genesAfter per os infection by BmNPV, BmIIM2,BmIIM3,BmIIM4 genes were up regulated or down regulated. The survival rates after per os inoculation of BmNPV by interference BmIIM1,BmIIM3,BmIIM4 genes were no significant differences compared with control. However, the survival rates after per os inoculation of BmNPV by interference BmIIM2 gene decreased significantly, it indicated that this gene had an important role in resistance to BmNPV in the silkworm.From all the results shown above, we found that although the IIM genes were few in number, they existed alternative splicings in the silkworm. Different IIM genes and different splicing forms had different roles in resisting to BmNPV. Meanwhile, RNAi confirmed preliminarily that only BmIIM2 gene had an important role in resistance to BmNPV in the silkworm.