Localization patterns of claudins in lactating goat mammary glands

Tight junctions (TJs) are crucial multiprotein complexes composed of occludin and claudin families between epithelial cells. TJs contribute to maintaining tissue barriers and cell polarity and regulating paracellular transport of water, ions and molecules. The claudin families determine permeability through paracellular pathways. The localization patterns of claudins differ depending on their structure or role. Herein, we examined the localization patterns of claudins in mammary glands of Tokara goats during lactation. Claudin localization in mammary alveoli, mammary ducts, and gland and teat cisterns was observed via immunofluorescence and claudin expressions were confirmed via western blotting of proteins from mammary glands, cultured goat mammary epithelial cells (GMECs), milk somatic cells, and blood leukocytes. TJ function was evaluated using the count of somatic cells and concentration of blood-derived components and ions in milk. Claudin-3 was localized at TJ regions in all structures. Claudin-4, -8, -10, and -16 were often localized at TJ regions. Localization patterns of several claudins differed between the teat cistern and other tissues, although concentrations of ions or blood-derived components did not differ. Conversely, somatic cell counts were highest in the last fraction of collected milk. Leukocytes in the lumen of mammary alveoli positively reacted against claudin-2, -12, and -15. Moreover, claudin-8 and -15 were detected in all samples (mammary glands, cultured GMECs, milk somatic cells, and blood leukocytes). Thus, the passive movement of ions or blood-derived components was appropriately regulated primarily through claudin-3 in each mammary gland structure while several claudins like claudin-8 and claudin-15 may be involved in controlling migration across the TJs of mammary epithelial cells.