Regulation of terminal hypertrophic chondrocyte differentiation in Prmt5 mutant mice modeling infantile idiopathic scoliosis

Idiopathic scoliosis (IS) is the most common type of musculoskeletal defect effecting children and is classified by age of onset, location, and degree of spine curvature. Although rare, the onset of IS during infancy is the more severe and rapidly progressive form of the disease, leading to increased mortality due to significant respiratory compromise. The pathophysiology of IS, in particular for infantile IS, remain elusive. Here, we show that PRMT5 is critical for the regulation of terminal hypertrophic chondrocyte differentiation in the spine and models infantile IS in mouse. Conditional ablation of PRMT5 in osteochondral progenitors led to impaired terminal hypertrophic chondrocyte differentiation and asymmetric defects of endochondral bone formation in the perinatal spine. Analysis of several markers of endochondral ossification revealed increased COLX and Ihh expression and a dramatic reduction of Mmp13 and RUNX2 expression in the intervertebral disc and vertebral growth plate. Furthermore, we demonstrate that PRMT5 function in committed chondrogenic lineages is required for regulation of COLX expression in the adult spine. Together, our results establish PRMT5 as a critical regulator of hypertrophic chondrocyte differentiation and endochondral bone formation in spine development and maintenance.