165. LOCATION OF ACTIVE TGFB1 IN THE MAMMARY GLAND DURING DIFFERENT STAGES OF DEVELOPMENT

Abstract

Development of the mammary gland involves complex interactions between epithelial and stromal cells under the influence of hormones and cytokines. Transforming growth factor beta 1 (TGFB1) is a multi-functional cytokine that we have reported to be essential for normal mammary gland development. TGFB1 is produced and secreted as part of a latent complex, and requires activation at the site of action to have biological effects. In situ hybridisation studies have shown mRNA encoding Tgfb1 is mainly expressed by mammary epithelium; however, the expression pattern of active TGFB1 in the mammary gland during different developmental stages is still unclear. Mammary gland tissue was collected from mice at puberty (5 weeks old), adult diestrus and late pregnancy (day 18 pc). Frozen sections were stained with antibody specifically reactive with active TGFB1 protein (not latent TGFB1 or other TGFB isoforms) for immunofluorescent analysis. Qualitative assessment of the staining revealed different patterns of active TGFB1 localisation depending on developmental stage. The strongest expression of active TGFB1 was observed in the mammary gland at diestrus compared to puberty and pregnancy. At diestrus, active TGFB1 was located around the surface of mammary epithelial cells. The staining was heterogeneous, with distinct zones of active TGFB1 accumulated around some but not all epithelial cells. During puberty, active TGFB1 was observed only within the lumen of the ducts. During late pregnancy, TGFB1 was homogenously distributed within the alveolar epithelium. The different patterns of active TGFB1 observed during puberty, diestrus and pregnancy suggest that TGFB1 has different roles in the mammary gland dependent on developmental stage.