R-SPONDIN²+ Mesenchymal Cells Form the Bud Tip Progenitor Niche during Human Lung Development

Functional experiments using organoid models, explant cultures, and FACS-isolated RSPO2+ mesenchyme showed that RSPO2 wass a critical niche cue that potentiated WNT signaling in bud tip progenitors to support their maintenance and multipotency.