Pancreatic amylase, chymotrypsin B, and trypsin I genes are specifically expressed in the exocrine pancreas. The 5'-flanking regions of these genes direct preferential expression of a linked reporter function (chloramphenicol acetyltransferase) in the pancreatic exocrine cell line AR4-2J. The sequences upstream of the amylase and chymotrypsin genes that are required for this cell specific activity possess the characteristics of transcriptional enhancers. We have mapped the regions responsible for enhancer activity by deletion analysis. Modification of specific nucleotide sequences within these regions can alter or eliminate enhancer function. Comparison of the 5'-flanking regions of nine genes expressed in the exocrine pancreas identifies a family of short related sequences. These sequences are located within the enhancer regions that we have mapped and may play a role in the regulation of the expression of pancreatic exocrine-specific genes.During cellular differentiation, different cell types acquire the ability to stably express characteristic sets of genes. The molecular mechanisms by which this occurs are poorly understood. The results of experiments involving transfection of exogenous genes into appropriate differentiated cells suggest that genes whose expression is restricted to a specific cell type contain cis-acting sequences that are required for efficient transcription in those cells (1-7). These elements resemble viral enhancers: they act in conjunction with separate promoter elements and can function in either orientation at a variable distance from the transcription initiation site. Unlike viral enhancers that can act in a variety of cell types, however, the activity ofthese cis-acting sequences appears to be restricted to a particular cell type. We have proposed that differentiated cells contain trans-acting proteins (differentiators) that interact with the specific cis-acting sequences to stimulate expression ofthe associated genes (1).We have used a linked reporter function, the bacterial enzyme chloramphenicol acetyltransferase (CAT) to conveniently distinguish expression of exogenous genes from that of the endogenous cognate gene in transient transfection assays. When recombinants containing the 5'-flanking regions of the insulin and chymotrypsin genes fused to the CAT coding region were transfected into various cells, high level CAT expression was observed only in (insulin-producing) endocrine B cells or (chymotrypsin-producing) pancreatic exocrine cells, respectively (1). In this report, we examine the upstream regions of the set of genes that is expressed specifically in pancreatic exocrine cells. We demonstrate that the amylase, chymotrypsin, and trypsin I genes possess upstream elements that direct preferential expression in the pancreatic exocrine cell line AR4-2J. The elements of the amylase and chymotrypsin genes, which have been mapped in detail, exhibit the properties of cell type-specific enhancers. Further, sequences within the 5'-flanking regions of seven other pancreatic ...

No abstract

No abstract

No abstract