A tyrosine kinase screen of mouse vestibular maculae.

Receptor tyrosine kinases allow extracellular signals to influence intracellular events, while other tyrosine kinases are involved in intracellular signalling. They may therefore be involved in the development, maintenance and repair of the sensory epithelia of the inner ear, since these are believed to be affected by inter- and intracellular signalling. In order to analyse possible tyrosine kinases expressed in sensory areas of the inner ear, a reverse transcription polymerase chain reaction screen of microdissected sensory epithelia was undertaken, using primers targeted at conserved sequences in tyrosine kinase domains. Tissue was taken from the maculae of the mouse vestibular organs, and consisted mainly of hair cells and their supporting cells. Of 80 clones sequenced, 49 coded for tyrosine kinases, and 11 for other known molecules. Further analysis of one of the sequences, for FGF receptor 4, showed a novel variant, expressed in the inner ear and elsewhere, with a variation in the intracellular domain which suggests differential activation of known signalling pathways. Other clones coded for tyrosine kinases expected to be involved in cell surface and intracellular signalling. The technique forms a powerful tool for analysing a range of the tyrosine kinases expressed, and provides a starting point for the analysis of cell-cell signalling in the inner ear.