Changes of endoplasmic reticulum and mitochondria in mammary epithelial cells during mammogenesis in Chinese Holstein dairy cows

The objective of the research was to study the changes of the major organelles, endoplasmic reticulum (ER) and mitochondria, in mammary epithelial cells of the Chinese Holstein dairy cow during mammogenesis. For this purpose, a mammary epithelial cell bank was established from 9 selected Chinese Holstein dairy cows using collagenase I digestion and attachment culture biotechniques. This cell bank included 9 samples at stages of pregnancy, lactation and involution. The changes of ER and mitochondria in the mammary cells were observed at the subcellular level using living cell fluorescent labeling and laser confocal microscopy. Subsequently, the area of integrated optical density of each sample was calculated to determine changes of ER and mitochondria in the mammary epithelial cells. The results showed clear differences in the epithelial major organelles during the various mammary gland development stages. The ER and mitochondria, as an indicator of lactogenic activity of alveolar secretory cells, increased in number from pregnancy to lactation by an average 37.32% and 18.44%, respectively, which was followed by a reduction at involution by an average 38.04% and 22.91% compared to lactation. Our study shows that the stages of mammogenesis are accompanied by changes in activity of the major organelles of the mammary epithelial cells.