Abstract: Maintenance of insect immune homeostasis requires prompt activation and down-modulation of the key transcriptional factors： Dorsal/Dif in Toll signaling pathway or Relish in IMD signaling pathway. Several regulatory molecules which modulate the stability or activity of the transcriptional factors in immune response have been identified in Drosophila and some other insects. Mutation or silencing of these molecules leads to over activation of immune system. So far there is no report about the regulatory molecules limiting immune signaling in the silkworm, Bombyx mori. In this study, several molecules which are predicted to be involved in immune homeostasis, including Wnt family members, Ubc9, FAF and POSH, were identified in the silkworm genome by comparative genomic analysis. The expression patterns of these molecules in multiple tissues after microbial infection were recorded, and the results showed that their expression levels generally decreased after microbial infection. Although an increase of more than 1.5-folds in expression level was observed in certain tissues, a rapid decrease followed and the high level was not maintained. Interestingly, the correspondence between the expression patterns of these molecules and the particular signaling pathway that microbes induced varied in different tissues. This is the first report of the regulatory molecules involved in silkworm immune homeostasis, which provides reference for further investigation on the molecular mechanism of immuno-negative modulation in the silkworm.

Key words: Silkworm, immune homeostasis, regulatory molecules, pathogen infection, expression pattern