Mouse xanthine dehydrogenase gene: structure and regulation in the mammary gland myoepithelial cell

The first part of the presentation is devoted to the discussion of the structural features of the mouse xanthine dehydrogenase gene (XD ). The exon/intron organization of XD gene is compared to that of the human aldehyde oxidase (AO) counterpart, whose product is another member of the molybdoflavoprotein family. In the second part of the talk, data on the tissue- and cell-distribution of the mouse XD protein and mRNA are presented. Attention is focussed on the fact that XD tissue-specific gene expression is different from that of AO. Finally, results on the molecular mechanisms regulating the expression of XD in the mouse mammary gland during pregnancy and lactation, are discussed. In the whole mouse, the cell type responsible for the expression of XD in the mammary tissues is the same one expressing β-casein, the prototype of milk proteins. In the HCl1 myoepithelial cell line, an excellent model in which to study the effects of lactogenic hormones, XD gene expression is under tight control by glucocorticoids and, to a lesser extent, by prolactin. The molecular mechanisms underlying XD expression in HCl1 cells show similarities as well as differences relative to what is observed for β-casein in the same experimental system.