The SOX9Y440X campomelic dysplasia mutation disrupts endolymph homeostasis

Abstract

The SOX9Y440X campomelic dysplasia mutation disrupts endolymph homeostasis. 1Irene.Y.Y. Szeto, 1Daniel Chu, 1Tiffany Au 2Yong-Heng Huang,1Sarah Wynn, 1Angel Mak, 1Y.S. Chan, 3Robin Lovell-Badge, 4Wood-Yee Chan, 2Ralf Jauch, 5Bernd Fritzsch 1Mai-Har Sham,1Kathryn.S.E. Cheah* 1School of Biomedical Sciences, The University of Hong Kong, Li Ka Shing Faculty of Medicine, 21 Sassoon Rd, Hong Kong, China.2Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences, 190 Kai Yuan Avenue, Science Park, Guangzhou, China 3Francis Crick Institute, Mill Hill Laboratory, The Ridgeway, Mill Hill, London, NW7 1AA, UK. 4School of Biomedical Sciences, The Chinese University of Hong Kong, Lo Kwee-Seong Integrated Biomedical Science Building, Area 39, Shatin, Hong Kong, China 5 Department of Biology, College of Liberal Arts & Sciences, University of Iowa, Iowa City, IA 52242, USA Mutations in SOX9 result in the skeletal malformation syndrome campomelic dysplasia (CD); deafness is found in some affected individuals but the molecular mechanisms underlying the hearing deficiency is unknown. We generated a mouse mutant carrying a conditional human campomelic dysplasia SOX9Y440X mutation which results in a truncated protein lacking the transactivation domain. The adult heterozygous Sox9Y440X/+ mice that express the mutation in the developing inner ear display sensorineural deafness and a lack of endocochlear potential. We show abnormal expansion of the endolymphatic compartment of the Sox9Y440X/+ mutant cochlea from E15.0 accompanied with overexpression of the water channel Aqp3 in the cochlea, out of a screen for candidate targets of the mutation. In addition to the cochlea, pendrin-expressing cells in the endolymphatic sac were also affected. These together upset the endolymph homeostasis in the inner ear, causing deafness.