The Importance of Epithelial-Stromal Interaction in Mammary Gland Development

The fact that two dissimilar tissues influence each other in their developmental behaviour is known to embryologists for a long time. The first experiments of Spemann, eventually establishing the phenomenon of “embryonic induction” were done some 80 years ago (1). Originally, the term was coined for events when two dissimilar tissues or blastemas come into close contact and, when as a result of this association, at least one of the two partners becomes determined for a new developmental pathway. A large number of such inductive events has been discovered since but, quite disappointingly, despite much effort not one system so far has yielded a biochemical or molecular factor that could be identified as mediator of induction.