Abnormal craniofacial and spinal bone development with col2a1a depletion in a zebrafish model of CHARGE syndrome

CHARGE syndrome patients commonly display craniofacial abnormalities. Furthermore, most patients show features of idiopathic scoliosis, reduced bone mineral density and in a few cases osteopenia. While several clinical cases and studies have documented the skeletal deformities in CHARGE syndrome bearing CHD7 mutations, the underlying mechanisms of the disorder remain elusive. Here, we detect and quantitatively analyze skeletal abnormalities in larval and adult chd7 -/- zebrafish. We show that young chd7 -/- larvae present with abnormal craniofacial development, especially related to cartilage. We also observe scoliosis-like spinal deformations at 9 dpf. Gene expression analysis confirmed the reduction of osteoblast markers and Pparγ targets. MicroCT analyses identified abnormal craniofacial structures, Weberian apparatus and vertebral body morphology in chd7 -/- mutants, with highly mineralized inclusions, along with significant variances in bone mineral density and bone volume. Notably, we detect a specific depletion of Col2a1a in the cartilage of craniofacial regions and vertebrae, in line with a significantly reduced number of chondrocytes. Our study is the first to elucidate the mechanisms underlying morphological changes in craniofacial structure and vertebrae of adult chd7 -/- zebrafish. The chd7 -/- mutant zebrafish will be beneficial in future investigations of the underlying pathways of both craniofacial and spinal deformities commonly seen in CHARGE syndrome. ### Competing Interest Statement The authors have declared no competing interest.