Plays an important role in bone formation and normal bone mineralization (PubMed:26207632, PubMed:22416756, PubMed:20025746). Promotes the differentiation of myoblasts into osteoblasts (PubMed:22416756, PubMed:20025746, PubMed:22579779). May induce the commitment and differentiation of myoblasts into osteoblasts through an enhancement of BMP2 production and interaction with the BMP-RUNX2 pathway (PubMed:21239498, PubMed:22579779). Up-regulates the expression of ATF4 which plays a central role in osteoblast differentiation (PubMed:24362451). Essential for normal spermatogenesis and late testicular differentiation (PubMed:26207632). Interacts with SMAD1, SMAD5 and RUNX2. Expressed in spermatocytes and spermatids in the developing testis (at protein level). Expressed in the brain, heart, lung, spleen, skeletal muscle, ovary, testis and epididymis (PubMed:26207632). Predominantly expressed in osteoblasts (PubMed:20025746). Highly expressed in early and late stage osteoblasts of developing embryos (at protein level). By parathyroid hormone (PTH) in osteoblasts (at protein level). Mice show a significant decrease in bone formation and bone mineralization and the mineralization defect is independent of calcium and phosphate metabolisms. Testis is smaller, sperm number is significantly decreased and testicular differentiation is perturbed (PubMed:26207632). Significantly reduced cortical thickness in the mid-shaft of the femur at postnatal day 14 (P14), and progressive bone hypoplasia after 8 weeks (PubMed:22416756).