Single cell RNA sequencing shows that cells expressing Sox9 postnatally populate most skeletal lineages in mouse bone.

In growing bones of mice, multiple cell types contribute to the osteoblast lineage, including growth plate chondrocytes, perichondrial cells and CXCL12-abundant reticular (CAR) marrow stromal cells. Here we use single-cell RNA sequencing and lineage tracing to show that all these osteoblast precursors, even postnatally, derive from Sox9-expressing progenitors. We also characterize a distinct group of chondrocytes located between the perichondrium and the columns of growth plate chondrocytes that contribute to the osteoblast lineage.