A Proteomic Analysis of Differentiation in the Mammary EpitheliumLaura Therese Strand While a great deal is known about the changing hormonal environment and the structural development of the mammary gland from pregnancy to lactation, very little is known about the molecular mechanisms governing differentiation of the mammary epithelium into a milk-secreting phenotype. It is important to acknowledge the diversity among the mammary glands of different species in order to better understand applications in human health and the dairy industry. In this study, we examined global protein expression during two states of differentiation in mammary epithelial cells from two species: in vitro proliferating and differentiated MAC-T cells (a bovine immortal cell-line), and primary mammary epithelial cells isolated from pregnant and lactating mice. When comparing the lists of proteins that differed in abundance in the two experiments, we observed many similarities in proteins related to structural dynamics and mRNA processing within these two mammary epithelial cell types. Intriguingly, we observed several differences in the regulation of metabolic proteins, highlighting the distinct pathways by which different species probably metabolize energy and synthesize milk components.v ACKNOWLEDGEMENTS