How array analysis can help us understand complex developmental switches: molecular regulation of the initiation of lactation

Abstract

Purpose of reviewThe purpose of this review is to describe recent results of global analyses that are beginning to provide a comprehensive picture of the complex biological switch that turns the quiescent mammary gland in the pregnant animal into an efficient milk secreting machine after birth of the young. This switch has been called secretory activation or lactogenesis II and is representative of developmental switches that initiate activity in a quiescent organ. Recent findingsMicroarray analysis of gene expression is a global approach that allows analysis of mRNA levels of thousands of genes simultaneously. Because of the massive data created a systematic approach is necessary, not only to identify changes in expression of genes that lead to the synthesis of milk components, but also to analyze changes in the tissue compartments within which the specialized proteins reside. The approach leads to generation of hypotheses about regulatory pathways and a framework for additional experiments targeted to protein interactions. While much more difficult, key studies are beginning to appear in this realm. Summary Global analysis of gene expression is a powerful tool for the generation of hypotheses about regulation of complex processes such as the initiation of lactation. When accompanied by structural and functional studies of specific genes and their products, it becomes possible to elucidate the role of specific molecular changes in activating milk secretion at parturition.