The use of transplanted mammary gland to study cancer signalling pathways

Mammary epithelium can be genetically manipulated by reconstituting a mammary gland, in an animal, from epithelium and a mammary fat pad from which the endogenous epithelium has been removed at 3 weeks of age. Genes can be introduced into the epithelium before transplantation using retrovirus vectors. To remove genes from the epithelium at present requires epithelium to be transplanted from knockout donor mice, but this is a valuable extension of knockout technology, as (a) it creates knockout epithelium in a normal stromal and systemic environment, or vice versa, and (b) where the knockout mouse does not survive into adulthood, epithelium can be rescued from embryos after about 12 days of gestation, and grown to form mature mammary epithelium in a normal recipient mammary fat pad.