Characterization of primary cilia distribution and morphology during lactation, stasis, and involution in the bovine...

Primary cilia are small, sensory organelles projecting from virtually all cells and are vital for cellular and tissue function. Their distribution in bovine mammary tissue has not previously been assessed, despite the potential for these organelles to provide specialized perceptive and regulatory functions to this acutely responsive and adaptive gland. The research objectives were to assess ciliary distribution and morphology during active lactation, milk stasis, and early involution using tissue samples obtained following the abrupt cessation of milk removal in nonpregnant, Friesian dairy cows at mid-lactation. Routinely processed tissue sections were obtained at intervals from 6 to 192 hr after the last milking (N = 3 animals per group) and assigned to active lactation (6-12 hr), milk stasis (18-36 hr), and early involution (72-192 hr). Primary cilia were observed in luminal secretory epithelial cells (SECs), myoepithelial cells, and stromal cells following fluorescent immunohistochemistry and confocal microscopy. In SECs, some primary cilia appeared deflected against the apical cell membrane. The proportion of those deflected was greater during milk stasis than active lactation. Data show that primary cilia were suitably placed in three important cell types to potentially coordinate various forms of signal transduction relying on both mechanosensation and chemosensation, according to the physical and physiological state of the gland. Their cell-type distribution and morphology provide new directions in the study of mammary regulation to enhance the understanding of how various mammary-specific cellular responses may be initiated by biochemical or local biophysical factors.