Analysis of DNase I-hypersensitive sites in the chromatin of the chicken C/EBPbeta gene reveals multiple cis-regulatory elements

CCAAT box/enhancer binding protein beta (C/EBPbeta), a member of the basic region-leucine zipper (bzip) class of transcription factors, plays important roles during differentiation of certain cell types, such as liver cells, fat cells and myelomonocytic cells. C/EBPbeta is highly expressed in these cell types, and activates specific genes during their differentiation. In the hematopoietic system, C/EBPbeta expression is restricted to the myelomonocytic lineage. To investigate the molecular basis of the cell-type specific expression of the C/EBPbeta gene in hematopoietic cells we have cloned the chicken C/EBPbeta gene and mapped DNase I hypersensitive sites (DHS) in the vicinity of the gene, using myelomonocytic as well as other cell types. We show that there are multiple nuclease-sensitive sites, most of which are cell-type specific, suggesting that they might act as cell-type specific cis-regulatory DNA elements. To study the possible function of these elements we have constructed reporter genes containing these sequences and analyzed their activity in different cell types. Our results show that several of the nuclease-sensitive regions act as cis-acting stimulatory elements in myelomonocytic but not in other cells. Taken together, our data suggest that the expression of the C/EBPbeta gene in myelomonocytic cells is controlled by multiple cell-type specific cis-acting sequences located both upstream and downstream of the gene.