Loss of Runx3 in osteoblasts provokes severe congenital osteopenia

Murine Runx3 is expressed in developing bone osteoblasts (OBLs) and its deletion in these cells culminates in severe congenital osteopenia. We demonstrate that Runx3 is non-redundantly involved in the proliferation of early pre-committed OBL progenitor cells, a critical step in the generation of adequate numbers of bone-forming OBLs. Thus, in the absence of Runx3 in cells of this lineage, the number of mature/active OBLs is significantly diminished, providing a mechanistic explanation to the observed osteopenia. This experiment was aimed at identifying genes that are likely regulated by Runx3 along osteoblastogenesis. To elucidate the Runx3-mediated transcriptional program along OBL differentiation, we compared gene expression profile in WT and Runx3f/f/Col1a1-cre calvarial OBLs. Progenitor cells were purified and RNA extracted, reverse-transcribed, fragmented, labeled and hybridized to GeneChip® Mouse Gene 2.0 ST Array.