Single-cell organogenesis captures complex breast tissue formation in three dimensions

Current breast organoid models, primarily based on self-assembly, face limitations in accurately mimicking the complex stages of tissue development, notably in replicating detailed tissue architectures and cellular diversity. Here, we demonstrate that a solitary human breast stem cell can, within a controlled hydrogel extracellular matrix environment, autonomously generate niche signals that drive directed organogenesis, producing organoids with mesenchymal and parenchymal components. This system surpasses traditional models by forming complex, heterogeneous ductal-lobular structures akin to those in native human breast tissue with the emergence of mesenchyme-like stroma. Using long-term, high-resolution live imaging, we quantitatively analyze the dynamic tissue development and morphogenesis, capturing cellular behaviors crucial for understanding both development and disease. The inclusion of patient-derived cells from diverse biological backgrounds, including pre- and post-menopausal donors, significantly enhances the applicability of the model. Our findings underscore that this controlled organogenesis approach represents a major leap over existing methods, offering a robust platform for probing the intricacies of human breast tissue development and its responses to environmental cues.