Abstract
Idiopathic scoliosis (IS) is the deformation and/or abnormal curvature of the spine that develops progressively after birth. It is a very common condition, affecting approximately 4% of the general population, yet the genetic and mechanistic causes of IS are poorly understood. Turner syndrome (TS) is caused by haploinsufficiency for a subset of genes within the pseudoautosomal region (PAR) at the tip of the short arm of the X chromosome thereby defining a critical interval for TS pathogenesis. Patients with TS present with a number of clinical features that individually represent common diseases, including an increased risk of developing IS and other skeletal symptoms. It is therefore important to assign genes within the TS critical interval to each of these disorders. Here, we focus on one gene within this interval, PPP2R3B, which encodes a protein phosphatase 2A regulatory subunit that interacts with the origin of replication component, CDC6. We found that PPP2R3B is expressed at sites of chondrogenesis within human foetuses, including the vertebrae and Meckel’s cartilage. As there is no rodent orthologue of PPP2R3B, we used CRIPSR/Cas9-mediated gene-editing to generate a frameshift mutation in zebrafish ppp2r3b. Adolescent zebrafish that were homozygous for this mutation exhibited a fully penetrant kyphoscoliosis phenotype which became progressively worse over time, mirroring IS in humans. These defects were associated with reduced mineralisation of vertebrae, resembling osteoporosis. Collectively, our data support a role for PPP2R3B haploinsufficiency in human IS pathogenesis in TS, establish a new animal model of this condition and provide a basis to investigate the underlying mechanisms.
Author Summary Abnormal curvature of the spine is extremely common, often developing as people age. The causes of this are not well understood and a major focus of active research is to identify the underlying genetic causes of this. In this study, we used gene-editing to create zebrafish carrying a mutation in the gene PPP2R3B. This is a gene linked to Turner syndrome in which patients develop spinal curvature, however, it has never been implicated in skeletal tissue maintenance before. Adolescent mutant zebrafish developed spinal curvature which became progressively worse, mirroring the human condition. This was associated with reduced formation of mineralised bone including an osteoporosis-like presentation within vertebrae. This work provides an experimental starting point to investigate the molecular and cellular mechanisms underlying spinal tissue integrity in future.