Transferrin and Prolactin Transcytosis in the Lactating Mammary Epithelial Cell

The mammary epithelial cell ferries constituentsoriginating from blood and from stromal cells, intomilk, by transcytosis. Morphological analysis of amembrane marker of transcytosis in the lactating mammary epithelial cell showed that very rapidendocytosis of surface membrane occurs from both thebasolateral and the apical side of the cell. In bothcases, membrane trafficking between endosomes and theGolgi complex allows communication between theendocytic and the biosynthetic pathways. Transferrin andprolactin are internalized in mammary cells andtransported through multivesicular bodies and Golgistacks. They are released into milk via different typesof secretory vesicles, prolactin being carried insecretory vesicles containing casein micelles.Consequences of the intracellular transport of theseproteins and physiological benefits for cell functionare discussed.