A distal region, hypersensitive to DNase I, plays a key role in regulatingrabbit whey acidic protein gene expression

The aim of the present study was to identify the functional domains of the upstream region of the rabbit whey acidic protein (WAP) gene, which has bee n used with considerable efficacy to target the expression of several forei gn genes to the mammary gland. We have shown that this region exhibits thre e sites hypersensitive to DNase I digestion in the lactating mammary gland, and that all three sites harbour elements which can bind to Stat5 in vitro in bandshift assays. However, not all hypersensitive regions are detected at all stages from pregnancy to weaning, and the level of activated Stat5 d etected in the rabbit mammary gland is low except during lactation. We have studied the role of the distal site, which is only detected during lactati on, in further detail. It is located within a 849 bp region that is require d to induce a strong expression of the chloramphenicol acetyltransferase re porter gene in transfected mammary cells. Taken together, these results sug gest that this region, centred around a Stat5-binding site and surrounded b y a variable chromatin structure during the pregnancy-lactation cycle, may play a key role in regulating the expression of this gene in vivo. Furtherm ore, this distal region exhibits sequence similarity with a region located around 3 kb upstream of the mouse WAP gene. The existence of such a distal region in the mouse WAP gene may explain the differences in expression betw een 4.1 and 2.1 kb mouse WAP constructs.