LOXHD1b knockout alters swimming behavior in zebrafish

Since human inner ear hair cells do not regenerate, the current treatments of hereditary deafness depend on hearing aids or cochlear implant. However, uncovering the functions of genes responsible for hereditary hearing loss is not only useful for their diagnosis but also for developing therapies. The pathogenetic mechanism of human non-syndromic deafness DFNB77 without morphological defects in the inner year caused by LOXHD1 mutations is not fully understood. We introduced zebrafish because the lateral line hair cells are structurally and physiologically similar to the human inner ear hair cells and mutations involved in non-symptomatic hearing loss can be assessed by their swimming behavior. The knock-out (KO) of LOXHD1b gene which is expressed in the lateral line hair cells was generated using the CRISPR-Cas9 system in zebrafish, and its morphological and functional changes were evaluated. As with human patients the LOXHD1b KO zebrafish larvae did not exhibit detectable morphological defects, but showed prolonged water flow sensing time. These results suggest that LOXHD1b plays pivotal roles for the hair cell neural activity and its KO zebrafish mutant serves as a useful model for revealing the molecular mechanisms linking LOXHD with hair cell function and for a drug screening to rescue the swimming phenotype.