| RNA interference(RNAi) is the processs of sequence- specific post-transcriptional gene silencing initiated by double-stranded RNA(dsRNA) that is homologous in sequence to the silenced gene. Many experiments have shown that RNAi is a powerful tool of studying the gene function in animals and plants.Consequently RNA interference was observed in C.elegans, It is extremely useful for those genes or organisms in which mutants are not easily obtained. In Bombyx mori, Quan G.X(GX.Quan et al,2002), Insect Biotechnology and Sericology Department, National institute of Agrobiological Sciences, Ibaraki, Japan, used silkworm Bombyx mori white gene (Bmwh3), approved that the RNA interference can be applied as a tool for the analysis of the gene function in Bombyx mori.The egg colour of wild-type is dark brown and white egg is mutant-type in Bombyx mori. Injection of double-stranded RNA (dsRNA) corresponding to the silkworm white gene (Bmwh3) into preblastoderm eggs of the wild-type silkworm induced phenotypes similar to those observed with mutants of the white egg 3 locus (10-19.6). The induced phenotypes were characterized by the presence of white eggs and translucent larval skin. To construct effective RNAi analysis technology in embryo of bombyx mori basing on predecessor, this article reviews the effect of RNA interference in different breeds and different methods of dsRNA mediated used the Bmwh3 gene, and researches the suitable dosage and stage of injecting dsRNA. We have discovered from the results that the dosage of 9.2nl(5.9ug/ul) injected dsRNA of Bmwh3 in embryo at 8h after oviposition by the method of microinjection can be induced mutant phenotype of White egg3. The preliminary results are the followings:1. In this work, we conclude from the results that the mechanism of sequence-specific degradation by dsRNA exists in the silkworm and that the injection of the dsRNA into eggs can be used to analyse gene function in the silkworm, injection of Bmwh3 dsRNA into preblastoderm eggs caused silencing of the Bmwh3 gene and induction the formation of the white eggs and translucent larvae phenotypes which were similar to white egg 3(w3)mutations.However, injection of plasmid of BmwhS gene and ddH2O did not depress the expression of the Bmwh3 gene. In the wild-type silkworm, the colour of eggs and eyes is dark brown. This colour is caused by the accumulation of ommochrome pigments. The introduction of dsRNA of BmwhS gene into the cells degraded mRNA of the corresponding gene.Accordingly, the protein can't express and the precursor of ommochrome pigment can't transport. Therefore, reduction of the accumulation of ommochrome pigments in the serous membrane may result in the formation inducted of white egg as well as brown and white mosaic eggs.2. G. X.Quan(GX.Quan et al,2002), the doctor of Insect Biotechnology and Sericology Department, National institute of Agrobiological Sciences, Ibaraki, Japan,used the bivoltine silkworm strain 200 as awild-type. The egg colour of the strain 200 is dark brown .They used the RNAi technique and succeeded to induce the mutants of the white egg 3.Its egg colour is light yellow and the larval skin is white and opaque.a.In this work,we used the bivoltine silkworm strain "da zhao"and succeeded as well.So,the RNAi worked effectively as a tool for the analysis of the gene function in the different breeds of Bombyx mori.3. In this work, we used microinjection and sperm mediated to inject dsRNA in embryos of Bombyx mori.The finding demonstrated that the microinjection can be applied for the induction of the Bmwh3 gene and induced sufficient dsRNA in embryos . But the sperm mediated cannot be induced mutant phenotype. Analysis on quantity of dsRNA, we injected the dsRNA of 5ul of 0.12ug/ul solution in spermatotheca of the female moth. We supposed that all of the dsRNA was entered into every embryo averagely, the corresponding molecules is roughly 2X106. This number is 2 multiple compare to G.X Quan et al (GX.Quan et al,2002) and it can be induced mutant of W3 enough.
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