Regulation of Mammary Gland Development by Tissue Interaction

Development of the mammary glands is initiatedin the embryo but the major part of their developmentoccurs in the adult. While development in puberty andpregnancy is dependent on hormones, prenatal and early postnatal development appear to progressautonomously. Mutual and reciprocalepithelial-mesenchymal interactions are critical forboth phases of development. Specific steps such as theformation of the bud, the first appearance of hormonereceptors, formation of the primary sprout and ductalelongation have been shown to be governed byepithelial-mesenchymal signaling. In recent years, someof the signaling molecules that are required in theseprocesses have been identified through geneinactivation. We discuss the potential role of thesefactors in mediating growth and differentiation. Inaddition we provide evidence that mammary epithelialcells from late embryonic stages are already capable ofsynthesizing milk proteins when subjected to appropriatehormonal stimulation.