Title

Runx2 protein expression utilizes the Runx2 P1 promoter to establish osteoprogenitor cell number for normal bone formation

UMMS Affiliation

Department of Cell Biology; Department of Orthopedics and Physical Rehabilitation

Date

8-26-2011

Document Type

Article

Medical Subject Headings

Animals; Bone Diseases, Developmental; Bone Diseases, Metabolic; Bone Regeneration; Calcification, Physiologic; Core Binding Factor Alpha 1 Subunit; Gene Expression Regulation; Mice; Mice, Transgenic; Osteoblasts; Osteogenesis; Promoter Regions, Genetic; Stem Cells

Disciplines

Cell Biology | Orthopedics

Abstract

The Runt-related transcription factor, Runx2, is essential for osteogenesis and is controlled by both distal (P1) and proximal (P2) promoters. To understand Runx2 function requires determination of the spatiotemporal activity of P1 and P2 to Runx2 protein production. We generated a mouse model in which the P1-derived transcript was replaced with a lacZ reporter allele, resulting in loss of P1-derived protein while simultaneously allowing discrimination between the activities of the two promoters. Loss of P1-driven expression causes developmental defects with cleidocranial dysplasia-like syndromes that persist in the postnatal skeleton. P1 activity is robust in preosteogenic mesenchyme and at the onset of bone formation but decreases as bone matures. Homozygous Runx2-P1(lacZ/lacZ) mice have a normal life span but exhibit severe osteopenia and compromised bone repair in adult mice because of osteoblastic defects and not increased osteoclastic resorption. Gene expression profiles of bone, immunohistochemical studies, and ex vivo differentiation using calvarial osteoblasts and marrow stromal cells identified mechanisms for the skeletal phenotype. The findings indicate that P1 promoter activity is necessary for generating a threshold level of Runx2 protein to commit sufficient osteoprogenitor numbers for normal bone formation. P1 promoter function is not compensated via the P2 promoter. However, the P2 transcript with compensatory mechanisms from bone morphogenetic protein (BMP) and Wnt signaling is adequate for mineralization of the bone tissue that does form. We conclude that selective utilization of the P1 and P2 promoters enables the precise spatiotemporal expression of Runx2 necessary for normal skeletogenesis and the maintenance of bone mass in the adult.

Rights and Permissions

Citation: J Biol Chem. 2011 Aug 26;286(34):30057-70. Epub 2011 Jun 15. Link to article on publisher's site

Related Resources

Link to Article in PubMed

PubMed ID

21676869