Experimental mouse genetics - answering fundamental questions about mammary gland biology

Contemporary gene-targeting techniques now make it possible to alter specif ic genes in the genome. As a result, a plethora of mouse models have been g enerated that allow researchers to dissect cell-signaling pathways involved in mammary gland development and in breast cancer. But what have we learne d so far? What do these models teach us? This review presents a global pict ure of how the analyses and comparison of individual knockout mouse models provide important insights into basic mammary gland biology. Particular emp hasis is placed upon what is currently known about the signaling pathways i nvolved in the establishment of the mammary ductal tree, and its subsequent proliferation at pregnancy and lactation. In addition to these well-establ ished pathways, we address recent data that describe the role of lesser-kno wn genes in the development of the mammary epithelium.