The prolactin gene hypersensitive sites are present early in development and are not induced by estrogen administration.

We have previously shown that two DNase I-hypersensitive sites are present upstream of the PRL gene in pituitary tumors of Fischer 344 rats. In this paper we present a method for examining hypersensitive sites in nontumorous pituitaries where PRL-producing lactotrophs comprise a small percentage of the total cell population. Using this method we are able to show that DNase I-hypersensitive sites in the PRL gene chromatin remain present even when estrogen is withdrawn from animals and PRL synthesis is markedly decreased. Furthermore, the hypersensitive sites appear before sexual development in female rats, and estrogen administration does not affect the appearance of the sites.