Modeling human limb skeletal development using human pluripotent stem cell-derived skeletal assembloids [ATAC-seq]
Despite recent advances in pluripotent stem cell-based approaches to induce skeletal cells, recapitulating human limb skeletal development in terms of structure and longitudinally oriented growth remains an unresolved challenge. Here, we report a method to differentiate human pluripotent stem cells into region-specific skeletal organoids harboring GDF5+PRG4+ interzone/articular chondrocyte progenitors (IZ/ACPs) and SP7+ growth plate chondrocytes (GPCs) via PRRX1? limb-bud mesenchymal cells. Comparative analysis demonstrated marked similarities of IZ/ACP and GPC organoids to the human embryonic limb, and graft fate and regenerative capacity in vivo were further characterized. We also mimicked the limb skeletal developmental process in a spatially structured manner by vertically positioning two IZ/ACP organoids at both ends of a GPC organoid to generate a human skeletal assembloid. Notably, this human skeletal assembloid recapitulated endochondral ossification with longitudinal skeletal growth upon transplantation. In summary, our study provides a novel research platform for human limb skeletal development and disease. Overall design: cells: hiPSC, LPM, LBM, ExpLBM, GPC organoids from hiPSCs (no TP), IZ/ACP organoids from hiPSCs (no TP).  ExpLBM and GPC organoids from hiPSCs (no TP)are triplicate. Other samples are each duplicate.