Expression of full-length Cochlin p63s is inner ear specific.
OBJECTIVE
The COCH gene mutated in DFNA9, murine an autosomal dominant hereditary hearing impairment, encodes Cochlin. Cochlin is also suggested to be the self-antigen of autoimmune sensorineural hearing loss. We previously reported that Cochlin constitutes 70% of the inner ear proteins and is classified into three types of isoform, p63s, p44s, and p40s. To study the specificity of expression of Cochlin isoforms in various organs, here we have investigated expression of the COCH gene at both the transcriptional and translational level.


METHODS
COCH gene expression was studied by RT-PCR and Southern blot analysis. Cochlin isoforms were studied by Western blot analysis using an isoform specific antibody.


RESULTS
At the transcriptional level, COCH mRNA was detected only in the inner ear by RT-PCR. Southern blot analysis of RT-PCR products detected a high level of COCH mRNA in the inner ear, lower level in spleen, and very low levels in the cerebrum, cerebellum/brain stem, eye, liver and kidney. At the translational level, Western blot analysis showed that a set of isoform, p63s, p44s, and p40s was detected at high levels only in the inner ear. In contrast, multiple proteins were detected at much lower levels in other organs tested. Notably, full-length Cochlin p63s was detected only in the inner ear.


CONCLUSIONS
Our findings demonstrate that the COCH gene is expressed preferentially in the inner ear and that expression of full-length Cochlin p63s is specific to the inner ear. These results will be central to understanding the function of Cochlin and its role in the pathophysiology of DFNA9.
Li
Lishu
L
Department of Otorhinolaryngology, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8603, Japan.
Ikezono
Tetsuo
T
Watanabe
Atsushi
A
Shindo
Susumu
S
Pawankar
Ruby
R
Yagi
Toshiaki
T
D000818:Animals; D001327:Autoimmune Diseases; D015153:Blotting, Western; D002417:Cattle; D007758:Ear, Inner / Q000378:metabolism*; D016326:Extracellular Matrix Proteins; D005260:Female; D015870:Gene Expression; D006319:Hearing Loss, Sensorineural / Q000235:genetics*; D006801:Humans; D009154:Mutation; D009928:Organ Specificity; D014176:Protein Biosynthesis; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D014158:Transcription, Genetic
C110668:COCH protein, human; D016326:Extracellular Matrix Proteins; D011506:Proteins; D012333:RNA, Messenger