The mammary gland is a highly dynamic organ that undergoes waves of proliferation, cell death and regeneration throughout female reproductive life. This activity requires the support of adult tissue stem/progenitor cells. The branched mammary epithelium is comprised of a basal cell layer surrounding an inner luminal cell layer. Lineage tracing studies have demonstrated that lineage-restricted progenitor cells maintain the luminal and basal compartments postnatally under physiological conditions. However, ’reprogramming’ of these cells causing the reacquisition of multipotency and generation of cells of the opposing lineage is triggered by certain conditions, including genotoxic (DNA) damage. This process, termed plasticity, is thought to play an important role in breast cancer. Thus, understanding how genotoxic damage affects mammary epithelial cell plasticity has the potential to improve breast cancer chemo-prevention and treatment. Here, I established 3D organoid cultures from transgenic lineage tracing mouse models that enable basal and luminal epithelial cell fate mapping to investigate genotoxic damage-induced fate plasticity. I showed that organoids faithfully recapitulate the in vivo structure and behaviour of mammary epithelial cells and confirmed their suitability for in vitro lineage tracing. Using 3D organoid culture, I demonstrated that cisplatin-induced DNA damage does not generate plasticity in basal or luminal cells in vitro. Interestingly, administration of cisplatin in vivo led to basal cell plasticity. This suggests that genotoxic damage-induced plasticity may be mediated by signals from the mammary microenvironment. Investigation of two candidate mediating factors, namely Interleukin-1ß and the TNF inhibitor Adalimumab that have previously been implicated in epithelial cellular plasticity, revealed that while IL-1ß failed to induce plasticity in basal or luminal cells in vitro, subtle evidence of basal cell plasticity was seen with Adalimumab treatment. Alongside, I interrogated available RNA sequencing data to identify novel putative microenvironmental factors mediating mammary cell plasticity that could be investigated in future studies.
The impact of genotoxic damage on mammary epithelial cell fate
Watson, E. O. (Author). 24 Jan 2023
Student thesis: Master's Thesis › Master of Science by Research (MScR)