A spatially-resolved blueprint of the developing human lung reveals a WNT-driven niche for basal stem cells

Organs are composed of diverse cell types that change across space and time during development. To interrogate this diversity, we micro-dissected developing human lungs along the proximal-distal axis during the late pseudoglandular stage and generated an integrated analysis of single-nucleus sequencing and spatial transcriptomics, creating a cellularly-resolved atlas of the lung. These rich datasets revealed positional niches and cellular heterogeneity along the proximal-distal axis, including the identification of a unique population of TP63 ⁺ basal cells, the primary stem cell of the airway, marked by expression of LGR5 and LGR6 . Analysis of the LGR5+ basal cell niche and functional experiments with primary organoid models suggest a tonic level of WNT pathway activity in LGR5 ⁺ basal cells that is potentiated by mesenchyme-derived R-SPONDIN. We found that basal cell self-renewal is enhanced by WNT activity, suggesting that the WNT pathway plays a previously unappreciated but critical role in airway stem cell maintenance during human development. These results enhance our fundamental understanding of the positional and cellular heterogeneity in the developing human lungs and begin to reveal unique niches that maintain homeostasis throughout the lung.