The tissue-specific regulation of the carboxyl ester lipase gene in exocrine pancreas differs significantly between mouse and human.

The carboxyl ester lipase (CEL) gene is highly expressed in exocrine pancreas and expression of the human CEL gene is mediated by a strong tissue-specific enhancer, which is absolutely necessary for high-level expression. The mouse promoter, on the other hand, does not contain a corresponding enhancer element, but instead is totally dependent on another pancreas-specific element. This element is identified as a pancreatic transcription factor 1 (PTF 1)-binding site. The human CEL promoter also contains a putative PTF 1 element located at a position corresponding to the essential PTF 1 site in the mouse promoter. However, nucleotide changes in the human promoter 5' flanking this PTF 1 site have created an overlapping CCAAT/enhancer-binding protein (C/EBP)-like binding motif, interfering with the binding of PTF 1. Hence, our findings provide an example of genetic divergence between species not accompanied by difference in function.