Reconstruction of Dynamic Mammary Mini Gland in vitro for Normal Physiology and Oncogenesis

Organoid culture has been extensively exploited for normal tissue reconstruction and disease modeling, however, it is still challenging to establish physiologically relevant architecture, size and functions in homeostasis. Here, we describe the development of a long-term adult stem cell derived mammary mini-gland culture system that supports robust 3D outgrowths recapitulating the morphology, cellular context, transcriptional heterogeneity of the normal mammary gland. The self-organization ability of stem cells and the stability of the outgrowths were determined by a coordinated combination of extracellular matrix, environmental signalings and dynamic physiological cycles. These mini glands are hormone responsive and reproduce the entire postnatal mammary development including puberty, estrous cycle, lactation and involution. Most intriguingly, these mini glands maintained the mammary stem cells and represented the fate transition from embryonic bipotency to postnatal unipotency in lineage tracing assays. In addition, induced oncogene expression in the mini glands drove the clinically relevant cancer initiation that can be monitored chronologically. Together, this study provides an experimental system fostering a dynamic organ miniature that can be studied chronologically and spatially for physiologically relevant biological processes with complexity. Single cell RNA profiles of mammary gland basal cells and luminal cells from primary mammary gland and mammary mini gland