Mechamisms of gene expression and physiological function of bombyxin

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1. Bombyxin genes of the silkmoth Bombyx mori encode insulin-related peptides and are expressed in four pairs of the neurosecretory cells in pars intercerebralis of brain. We identified two transcription elements for the cell-specific expression of bombyxin F1 gene. One of the elements, BOSE, was essential for the cell-specific expression and localized in the region from -170 to -159 bp upstream of the translation start site of the F1 gene. The other element, activator element, was responsible for increasing the expression level and located in the region from -185 to -181 bp.2. The expression of bombyxin genes showed a gene-arrangement-dependent manner. The family A and C genes expressed are located exclusively in the gene pairs but not in the gene triplets. The family B genes belonging to the gene triplets are expressed. In the gene pairs, some family B genes are expressed, whereas the other family B genes are not expressed. By reporter gene analysis using various bombyxin gene promoters, we confirmed the gene-arrangement-dependent manner of the expression of the bombyxin family A and C genes. The expression manner of bombyxin genes are unique but the mechanisms of the expression remains to be elucidated.3. We examined the silkworm baculovirus expression vector system for the in vivo expression of the GFP gene under the control of several gene promoters, including the bombyxin promoter and the prothoracicotropic hormone (PTTH) gene promoter. Depending on the neurohormone gene promoters used, the GFP gene is correctly and specifically expressed in the neurosecretory cells of the brain. This result indicates that thesilkworm baculovirus expression vector system can serve as an efficient system permitting gene delivery into neural tissues in insects.