Loss of Chd7 function in gene-trapped reporter mice is embryonic lethal and associated with severe defects in multiple developing tissues

CHD7 is a novel chromodomain gene mutated in 60%-80% of humans with CHARGE syndrome, a multiple congenital anomaly condition characterized by ocular coloboma, heart defects, atresia of the choanae, retarded growth and development, genital hypoplasia, and characteristic ear abnormalities including deafness. Phenotypic features of CHARGE are highly variable and incompletely penetrant. To explore developmental roles of CHD7, we generated mice carrying the Chd7 Gt allele from a Chd7-deficient, gene-trapped lacZ reporter ES cell line. RT-PCR of embryo RNA demonstrated significantly reduced levels of wild-type transcript in Chd7 Gt/Gt embryos. Chd7 Gt/Gt embryos survive only up to embryonic day 10.5 (E10.5). Chd7 Gt/⁺ male and female mice are viable, small, and exhibit variable degrees of head-bobbing and circling, consistent with vestibular dysfunction. Paint-filling of E16.5 heterozygous inner ears revealed defects of the semicircular canals. The pattern of β-galactosidase activity in Chd7 Gt/⁺ embryos mimics Chd7 mRNA expression in wild-type embryos, confirming the fidelity of the lacZ reporter. We observed tissue-specific β-galactosidase in the E12.5 and E14.5 Chd7 Gt/⁺ brain, pituitary, ear, heart, and craniofacial structures, indicating survival of Chd7 Gt/⁺ cells in CHARGE-relevant organs. These studies demonstrate the utility of Chd7 Gt as a reporter-tagged loss-of-function allele for future studies exploring developmental mechanisms of Chd7 deficiency.