Fig. 4.

ECR5^KO mice have HBM due to reduced number of Sost-expressing osteocytes. ECR5 was replaced by a neo cassette, which was subsequently removed by Cre recombinase to generated ECR5^KO mice (A). ECR5 targeting was confirmed by Southern blot (B). μCT analysis showed significant differences between ECR5^KO mice and WT control littermates (C–H) consistent with ECR5^KO mice having HBM. Fewer osteocytes expressed Sost in ECR5^KO mice (L) compared with WT (I); (Upper) protein signal (green channel); (Lower) the same section visualizing nuclei with DAPI (blue channel). Quantitative assessment of the number of cortical osteocytes expressing Sost in ECR5^KO relative to WT identified a ∼30% reduction in Sost-positive cells, in ECR5^KO mice (K). Yellow arrows point to Sost-positive cells; white arrows point to Sost-negative osteocytes.