The Role Of RNA Binding Protein Rbm24 In Maintenance Of Auditory And Motor Coordination Functions Of Inner Ear

In eukaryotes,the most prominent feature of the genome is the split arrangement of the gene coding sequence.The precursor mRNA needs to go through a series of cutting,splicing,and modification processes to finally form mature mRNA.These processes enable the production of multiple isoforms of mRNA from single genes,which greatly enriches the gene diversity.Alternative splicing is thought to play important roles in the development of tissues and organs and the process of biological evolution.The inner ear is an important organ for humans and higher animals to sense sound and maintain the balance of body movement.It functions in converting mechanical signals of sound and movement into electrical signals,which depend on hair cells.Up to now,studies on the mechanism of the development and function regulation of inner ear hair cells have mainly focused on the transcriptional level,while studies on the posttranscriptional regulation,especially the alternative splicing,have rarely been reported.In our early wholemount in situ hybridization experiment on mouse embryos,we found that an alternative splicing factor Rbm24 was highly expressed in the inner ear,which attracted our attention and prompt us to speculated whether Rbm24 could affect the inner ear function as a post-transcriptional regulator.Therefore,we studied the function of Rbm24 in the inner ear and constructed Rbm24 induced knockout mice.Since Rbm24 knockout mice were embryos lethal,we knocked down Rbm24 expression by injection of TMXF after birth.About one month after Rbm24 knockout,we found that Rbm24 knockout mice developed significant vestibular dysfunction,showing involuntary nodding and circling-like behaviors,and the motor coordination function of the mouse defected.In addition,the auditory function of mice were also lost,as measured by the auditory brainstem response(ABR)test.Further,we studied the pathological changes of the inner ear and found that a large amount of both cochlea and vestibular hair cells were apoptotic,and the degeneration of hair cells were more serious with the prolongation of time.In particular,in all types of inner ear hair cells,we found the stereocilia of hair cells were significantly lost and disorganized.Through high throughout RNA sequence,we studied the transcriptome changes in response to Rbm24 knockout in inner ear hair cells and found the alternative splicing of a large number of stereocilia-related genes were significant changes.In addition,we also found significant alterations in alternative splicing of many genes related to inner ear hair cell survival,including potassium channel proteins KCNQ4 and calcium channel proteins ATP2B2.Further,we verified that the alternative splicing events regulated by Rbm24 are inner ear specific by RT-PCR,suggesting that Rbm24 is also an inner ear specific alternative splicing regulator.In addition to alternative splicing changes,we found that mRNA expression levels of synaptic related genes were significantly changed in the inner ear,suggesting that Rbm24 knockout may also affect inner ear synaptic structure.In conclusion,our study revealed that Rbm24 plays an important role in the maintainance of auditory and motor coordination functions of the inner ear,and the alternative splicing events regulated by Rbm24 play an important role in the survival of inner ear hair cells and maintenance of stereocilia morphology.Given the important role of Rbm24 in inner ear function,this suggests that RBM24 may be a mutation site in human congenital deafness.