GENOMIC REGULATION OF BOVINE MAMMARY EPITHELIAL CELL GROWTH AND DIFFERENTIATION

Abstract

The goal of this dissertation was to evaluate genomic regulation during bovine mammary epithelial cell (BMEC) growth and differentiation. To accomplish this goal, a collagen gel cell culture system was developed that was capable of mimicking the prepartum stages of epithelial development and differentiation. In addition, a 4,600-cDNA bovine microarray was developed in order to profile gene expression. Analysis of BMEC in collagen cultures using various lactogenic conditions highlighted the critical importance of both hormonal and structural signals. The objective of the first study utilizing the microarray was to evaluate the contribution of the two prominent lactogenic factors in vitro, 1) prolactin and 2) gel release. Collectively, lactogenic stimulation appears to turn off genes associated with structural progression and morphogenesis, and turn on genes involved in alveolar MEC differentiation such as cell polarization, milk protein synthesis and ER/Golgi transport. The objective of the second study utilizing these resources was to evaluate the direct effects of thermal stress on BMEC growth and development. The structural response to thermal stress was characterized by morphogenic inhibition and dramatic regression of the ductal branches. Microarray analysis revealed an overall up-regulation of genes associated with stress response, DNA repair, protein degradation and cell death. In contrast, genes associated with cellular and MEC-specific biosynthesis, metabolism, and morphogenesis, were generally down-regulated. Subsequent to the analysis of BMEC differentiation was a targeted effort focusing on two small molecules hypothesized to be involved in regulating the BMEC secretory response: serotonin and prostaglandin E2. A pilot study suggested that serotonin is produced by bovine MEC and a model was proposed that describes serotonin's role as a feedback inhibitor during milk synthesis and secretion. A second pilot study demonstrated that PGE2 had a consistently positive influence on lumen diameter of alveolar structures in vitro. Overall, this dissertation provides new resources for studying bovine functional genomics, particularly within the mammary gland, and it provides a strong foundation for understanding genomic regulation of mammary epithelial structure and function. Furthermore, it establishes potential roles for local regulation of milk production by serotonin and PGE2.