Expression and function of Dlx genes in the osteoblast lineage

AbstractOur laboratory and others have shown that overexpression of Dlx5 stimulates osteoblast differentiation. Dlx5−/−/Dlx6−/− mice have more severe craniofacial and limb defects than Dlx5−/−, some of which are potentially due to defects in osteoblast maturation. We wished to investigate the degree to which other Dlx genes compensate for the lack of Dlx5, thus allowing normal development of the majority of skeletal elements in Dlx5−/− mice. Dlx gene expression in cells from different stages of the osteoblast lineage isolated by FACS sorting showed that Dlx2, Dlx5 and Dlx6 are expressed most strongly in less mature osteoblasts, whereas Dlx3 is very highly expressed in differentiated osteoblasts and osteocytes. In situ hybridization and Northern blot analysis demonstrated the presence of endogenous Dlx3 mRNA within osteoblasts and osteocytes. Dlx3 strongly upregulates osteoblastic markers with a potency comparable to Dlx5. Cloned chick or mouse Dlx6 showed stimulatory effects on osteoblast differentiation. Our results suggest that Dlx2 and Dlx6 have the potential to stimulate osteoblastic differentiation and may compensate for the absence of Dlx5 to produce relatively normal osteoblastic differentiation in Dlx5 knockout mice, while Dlx3 may play a distinct role in late stage osteoblast differentiation and osteocyte function

THE USE OF AN ETHIDIUM ANALOGUE IN THE DYE-BUOYANT DENSITY PROCEDURE FOR THE ISOLATION OF CLOSED CIRCULAR DNA: THE VARIATION OF THE SUPERHELIX DENSITY OF MITOCHONDRIAL DNA

The separation between open and closed circular DNA in buoyant CsCl gradients containing intercalating dyes depends on the superhelix density of the closed form. These separations are about 1.8 times larger with propidium iodide than with ethidium bromide. The superhelix densities of mitochondrial DNA from HeLa cells and Lytechinus pictus eggs appear to be about two thirds that of mitochondrial DNA from rat and rabbit liver