Effect of deletion of the DNase I hypersensitive sites on the transcription of chicken Ig-β gene and on the maintenance of active chromatin state in the Ig-β locus

The role of DNase I hypersensitive sites (DHSs) in transcription of the B cell-specific Ig-β gene and in maintenance of active chromatin state in the Ig-β locus were examined. A total of 10 DHSs were divided into four regions, and each region was deleted separately in chicken B lymphocyte-derived DT40 cells. Deletion of three DHSs located between the Ig-β promoter and its upstream Na channelgene, resulted in the absence of Ig-β mRNA. Three regions except the region in the Na channel gene were involved in the transcription of Ig-β gene. The enhancing activity of DHSs as determined by transient transfection assays did not always correlate with the effect of DHS deletion on the expression level of Ig-β mRNA. In each deletion, cells contained the same DHSs as observed in the predeletion cells, indicating that deleted DHSs did not participate in the maintenance of DT40-specific DHSs. Enhanced acetylation of H3 and H4 histones at the Ig-β promoter and at DT40-specific DHSs was observed in cells in which DHSs between the Na channel gene and Ig-β promoter were deleted; therefore, these DHSs are prerequisite for transcription of the Ig-β gene but not required for the maintenance of active chromatin state in the Ig-β locus. Thus, epigenetic factors required for the maintenance of the active chromatin state are suggested to reside in other regions than those deleted in this study.