Changes of DNaseI Sensitivity of the Fibroin and Sericin Genes during the Silkworm Development. (DNaseI sensitivity/gene expression/silk gland/chromatin structure)

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Abstract
DNasel sensitivity assay of the fibroin gene and the sericin gene in different tissues along developmental stages have revealed unique patters of regulation. In the posterior silk gland the fibroin gene was more sensitive to DNaseI at the larval feeding stages, when the gene is transcriptionally active, than at the larval molting stages, when the gene is inactive. In the middle silk gland and the ovarian tissue where the fibroin gene is suppressed throughout development, the gene was found to be resistant to DNaseI. On the other hand the sericin gene remained rather DNaseI sensitive in the middle silk gland through larval development, where transcription activity of the gene changes drastically. Disappearance of DNaseI sensitivity of the fibroin gene at the fourth molting stage takes place earlier than the decline of the fibroin gene transcription. However, in the fifth feeding stagereappearance of DNaseI sensitivity occurs synchronously with resumption of the fibroin gene transcription. Thus a constitution of the DNaseI sensitivity may be required, but not sufficient to support an active state of genes.