Hox genes in the adult skeleton: Novel functions beyond embryonic development.

Hox genes encode evolutionarily conserved transcription factors that control skeletal patterning in the developing embryo. They are expressed in regionally restricted domains and function to regulate the morphology of specific vertebral and long bone elements. Recent work has provided evidence that Hox genes continue to be regionally expressed in adult tissues. Fibroblasts cultured from adult tissues show broadly maintained Hox gene expression patterns. In the adult skeleton, Hox genes are expressed in progenitor-enriched populations of mesenchymal stem/stromal cells (MSCs), and genetic loss-of-function analyses have provided evidence that Hox genes function during the fracture healing process. This review will highlight our current understanding of Hox expression in the adult animal and its function in skeletal regeneration. Developmental Dynamics 246:310-317, 2017.