Deletion of Dock7 Exons 3 and 4 Results in Reduced Trabecular Microarchitecture and a Decrease in Mineralization

Dedicator of Cytokinesis 7 (DOCK7) has recently emerged as a regulator of skeletal homeostasis, but existing Dock7 mutant models harbor only global mutations and are incompatible with tissue-specific deletion studies. We previously generated a Dock7-floxed allele in which exons 3-4 are flanked by LoxP sites. To validate the utility of this allele for future conditional strategies, we globally deleted exons 3-4 to generate Dock7em2/em2mice and characterized their skeletal phenotype. Dock7em2/em2mice exhibited a diluted coat color and white belly spot, consistent with spontaneous Dock7 mutations. Bone microarchitecture was assessed in 21-week-old males and females. Global deletion of Dock7 exons 3-4 resulted in a 30-37% reduction in trabecular bone volume in the distal femur and L5 vertebrae. Cortical bone thickness was unchanged in both sexes; however, male Dock7em2/em2mice displayed reduced total femoral area, whereas females showed increased medullary area. These data suggest altered appositional bone growth with mutation of Dock7. To assess osteoblast function, bone marrow stromal cells (BMSCs) were differentiated in vitro. Dock7em2/em2 BMSCs exhibited reduced mineralization and decreased Bglap expression, indicating attenuated osteoblast differentiation. These findings demonstrate that Dock7 exons 3-4 are required for normal trabecular bone acquisition and osteoblast function. Loss of these exons disrupts DOCK7 activity, supporting the Dock7em2/em2 line as a valid loss-of-function model. The Dock7em2/em2 mouse provides a foundation for future tissue-specific deletion studies to define the cellular roles of DOCK7 in regulating bone formation and trabecular architecture.