PgmNr Z548: Assembling the MET complex in sensory hair cells: Tomt regulates the trafficking of Tmc proteins to the site of mechanotransduction.

Authors:
Timothy Erickson 1 ; Elisabeth Busch-Nentwich 2 ; Jennifer Olt 3 ; Katherine Hardy 3 ; Reo Maeda 1 ; Rachel Clemens-Grisham 1 ; Alex Nechiporuk 1 ; Walter Marcotti 3 ; Teresa Nicolson 1


Institutes
1) Oregon Health and Science University, Portland, OR; 2) Wellcome Trust Sanger Institute, Cambridge, UK; 3) University of Sheffield, Sheffield, UK.


Abstract:

The mechanoelectrical transduction (MET) complex is a multimeric transmembrane protein assembly that allows sensory hair cells to convert mechanical stimuli into electrical signals. Members of the complex include the tip link proteins PCDH15 and CDH23, as well as MET channel subunits LHFPL5, TMIE and TMC1 / 2. Although the identity of the ion channel that mediates MET is controversial, genetic and molecular evidence shows that Transmembrane channel-like proteins (TMC1 and TMC2) play an essential role in the MET complex, possibly acting as the pore-forming subunits of the channel. How the TMCs and other MET proteins assemble into a functional unit is a major outstanding question in the field of hearing research.

Transmembrane O-methyltransferase (TOMT / LRTOMT) is a human deafness gene responsible for non-syndromic deafness DFNB63. However, the specific role that TOMT plays in hair cells is not known. We found the zebrafish ortholog of tomt (mercury) in a mutagenesis screen for deafness and balance mutants in zebrafish. Tomt-deficient hair cells have normal morphology, but do not have functional mechanotransduction. GFP-tagged Tomt is enriched in the Golgi, and excluded from the site of MET in the apical hair bundle of hair cells. Since Tomt is not a part of the MET complex itself, we reasoned that it functions in the Golgi to regulate the trafficking of other MET components to the hair bundle. Tomt is not required for the normal trafficking of Pcdh15a, Lhfpl5a, or Tmie. However, we found that GFP-tagged Tmc1 and Tmc2b proteins are specifically excluded from the hair bundle in Tomt mutants. Transgenic expression of Tomt is sufficient to restore MET to mutant hair cells, and to restore Tmc localization in the hair bundle. Thus, we propose a model of MET complex assembly where Tomt methyltransferase activity is required for the correct trafficking of Tmc proteins in sensory hair cells.



ZFIN Genetics Index
1. mrc
2. tmc1
3. tmc2a
4. tmc2b
5. lhfpl5a
6. tmie
7. pcdh15a
8. cdh23