Optimization of 3D organoid culture to study the effects of pregnancy hormones on the epigenome and transcriptional output of mammary epithelial cells

Abstract: The use of mouse derived mammary organoids can provide a unique strategy to study mammary gland development through a normal life cycle, as well as offering insights into how malignancies form and progress. Substantial cellular and epigenomic changes are triggered in response to pregnancy hormones, a reaction that engages molecular and as well as transform the mammary epithelial cells into milk producing machines. Such epigenomic alterations remain stable in post-involution mammary epithelial cells and control a reactivation of gene transcription in response to re-exposure to pregnancy hormones. Thus, a system that tightly controls exposure to pregnancy hormones, epigenomic alterations and activation of transcription would allow for a better understanding of such molecular switches. In addition, such system may provide a valuable resource to expand our understanding of pregnancy-induced development to other model systems, including humans. Here, we describe the optimization of ex vivo cultures to mimic the response of mammary organoid cultures to pregnancy hormones, and to understand gene regulation and epigenomic reprogramming on consecutive hormone exposure. Our finding suggest that this system yields similar epigenetic modifications to those reported in vivo, thus representing a suitable model to track closely epigenomic rearrangement and to define unknown players of pregnancy-induced development.