Figure 6.

Looping model for CFTR gene. In CFTR-expressing cell types, such as primary epididymis cells, elements in the CFTR 3' flanking region are in close proximity with the CFTR promoter. This 3' flanking region includes the tissue-specific +6.8-kb DHS, shown here to bind CTCF, as well as other previously described DHS (13,6). Protein factors bound at each of these sites interact with the promoter-bound transcription machinery, thus forming an active chromatin hub (ACH) and helping regulate expression of the CFTR gene. In addition to DHS from the 3' flanking region, intronic DHS such as the intestine-specific intron 1 element (31,42,43) and others (represented by the elements marked ‘?’), may contribute to the CFTR ACH in a tissue-specific manner.