Preliminary Study Of The Role Of CIB1 And CIB2 In The Auditory System Using Knockout Mice

Calcium and integrin-binding protein 2(CIB2)belongs to a protein family with four members,CIB1 through CIB4,which are characterized by multiple calcium-binding EF-hand domains.Most studies about this protein family were focused on CIB1,which was found to play important roles in various cellular and physiological processes such as cell proliferation,apoptosis,angiogenesis and cytoskeleton organization.In addition,some studies showed that mutations in the human CIB2 gene are associated with nonsyndromic deafness DFNB48 and syndromic deafness USH1J.Our studies also showed that among the family members the Cibl and Cib2 genes are expressed in mouse cochlear hair cells.To further explore the function of CIB1 and CIB2 in hearing,we established Cibl and Cib2 knockout mice using the clustered regularly interspaced short palindromic repeat-(CRISPR)-associated Cas9 nuclease(CRISPR/Cas9)genome editing technique.Our results showed that the Cibl knockout mice have normal hearing while the Cib2 knockout mice show profound hearing loss.Further investigation revealed that hair cell stereocilia development is affected by knocking out of Cib2.Stereociliary bundle fragmentation was observed and the second row stereocilia are over-grown in many Cib2-/-outer hair cells(OHCs).The kinocilia of inner hair cells(IHCs)are not retracted properly in P20 Cib2 knockout mice.Furthermore,loss of CIB2 abolishes mechanoelectrical transduction(MET)currents in OHCs.In conclusion,we show that although both CIB1 and CIB2 are detected in mouse cochlea,only loss of CIB2 results in hearing loss.CIB2 plays indispensable role in stereocilia development and auditory hair cell MET.