SECRETORY ACTIVATION AND LACTOGENESIS - ARE ALL CELLS EQUAL?

The overarching goal of this project is to define the importance of a population of unique cells within the udder that have double the number of nuclei of so-called normal cells. These "binucleated" cells (BNC) were recently identified as being present in the mammary glands of lactating mice, raising the question of their role in the glands of other lactating domestic livestock. The potential significance of these cells for a range of animal industries relying on milk production cannot be overstated. A number of biological and physiological examples and arguments support our proposal that the recruitment and/or maintenance of BNC in the lactating MG are key drivers of milk output. Our overarching hypothesis is that the abundance of BNC in the lactating MG directs its lactational capacity. In Aim 1 we will define the BNC population within the MG of livestock and its relationship to lactational performance. Given a paucity of information regarding BNC distribution in species other than mice, we will first determine their abundance in the MG of pigs and dairy cattle during specific stages of lactation. We will then establish whether BNC abundance accounts for persistent alterations in the milk production capacity of cows and pigs after different interventions that persistently modify lactational output. In Aim 2 we will ask the question of whether binucleation directly affects milk production potential. While associations between BNC frequency and milk production potential will be established from Aim 1, we plan to directly test that relationship here. We will block mitosis while also tracing whether DNA that is replicated during lactogenesis. We will then use explant culture to test whether a blockade of mitosis impacts the responsiveness of MEC/BNC to lactogenic stimulation. In Aim 3 we will establish if epithelial cell populations within the lactating mammary glands are transcriptionally different. Here we will use cell sorting followed by RNASequencing and single cell RNASequencing to establish how these populations of MEC, and the cells within them, vary at the transcriptomic level. Combined, these experiments stand to clearly and collectively establish how the BNC population within the MG of domestic livestock is temporally-altered during lactogenesis, its role in the milk production potential of the MG, and the transcriptional differences that exist between BNC and MNC.