Physiology of lactation: Old questions, new approaches

One of the major advances in the study of endocrine regulation of the mammary gland has been the development of techniques to obtain defined mutations in mice. The use of mice deficient in hormones, growth factors, receptors or transcription factors now allow to dissect hormonal pathways and to elucidate the specific role of the epithelium and the stroma. The study of temporal changes of global gene expression at each physiological stage is now possible by microarrays or proteomic analyses to profile gene or protein expressions, respectively. These approaches have been successful in demonstrating the huge number of genes that are differentially expressed in the murine and bovine mammary epithelial cells during pregnancy, lactation and involution. The next step to get the temporal and spatial assignement of gene function necessitate now the coordination of these technologies with accurate cellular biology approaches through in vivo and dynamic studies.