Generation of Ext1 Gene-Edited Mice Model Via Dual sgRNAs/Cas9 System and Phenotypic Analyses

Hereditary multiple exostoses (HME) is an autosomal dominant skeletal disease. Genetic linkage analyses have identified that mutations in the exostosin glycosyltransferase (EXT)1 and EXT2 genes are linked to HME pathogenesis, with EXT1 mutation being the most frequent. The aim of this study was to generate a mice model with Ext1 gene editing to simulate human EXT1 mutation and investigate the genetic pathogenicity of Ext1 through phenotypic analyses. We designed a pair of dual sgRNAs targeting exon 1 of the mice Ext1 gene for precise deletion of a 46 bp DNA fragment, resulting in frameshift mutation of the Ext1 gene. The designed dual sgRNAs and Cas9 proteins were injected into mice zygotes cytoplasm. A total of 14 mice were obtained via embryo transfer, among which two genotypic chimera mice had a deletion of the 46 bp DNA fragment in exon 1 of the Ext1 gene. By hybridization and breeding, we successfully generated heterozygous mice with edited Ext1 gene (Ext^+/-). Off-target effect analysis did not reveal off-target mutations in Ext^+/- mice caused by the two sgRNAs used. Compared to wild-type mice, Ext^+/- mice exhibited lower body weights. X-ray imaging showed hyperplastic bone near caudal vertebrae only in male Ext^+/- mice, with computed tomography values approximately at 200 HU for hyperplastic bone between ribs and spine regions. Furthermore, immunohistochemical analysis revealed fewer articular chondrocytes expressing EXT1 in edited mice compared to wild-type ones. Pathological section analysis demonstrated no structural or morphological abnormalities in heart, liver, lung, or kidney tissues from Ext^+/- mice. In conclusion, we successfully generated an accurate DNA deletion model for studying Ext1 using dual sgRNAs/Cas9 systems. In conclusion, we successfully generated precise DNA deletions in the Ext1 mice model using the dual sgRNAs/Cas9 system. In conclusion, we observed significant phenotypic changes in Ext^+/- mice, particularly bone hyperplasia in male individuals; however, no exostosis was detected in the gene-edited mice. The introduction of a frameshift mutation into the Ext1 gene through CRISPR/Cas9 technology resulted in novel phenotypic alterations, highlighting the genetic pathogenicity of Ext1. Therefore, our Ext^+/- mice serve as a valuable model for further biomedical investigations related to the Ext1 gene.