The supporting-cell antigen: A receptor-like protein tyrosine phosphatase expressed in the sensory epithelia of the avian inner ear

After noise- or drug-induced hair-cell loss, the sensory epithelia of the a vian inner ear can regenerate new hair cells. Few molecular markers are ava ilable for the supporting-cell precursors of the hair cells that regenerate , and little is known about the signaling mechanisms underlying this regene rative response, Hybridoma methodology was used to obtain a monoclonal anti body (mAb) that stains the apical surface of supporting cells in the sensor y epithelia of the inner ear. The mAb recognizes the supporting-cell antige n (SCA), a protein that is also found on the apical surfaces of retinal Mul ler cells, renal tubule cells, and intestinal brush border cells. Expressio n screening and molecular cloning reveal that the SCA is a novel receptor-l ike protein tyrosine phosphatase (RPTP), sharing similarity with human dens ity-enhanced phosphatase, an RPTP thought to have a role in the density-dep endent arrest of cell growth. In response to hair-cell damage induced by no ise in vivo or hair-cell loss caused by ototoxic drug treatment in vitro, s ome supporting cells show a dramatic decrease in SCA expression levels on t heir apical surface. This decrease occurs before supporting cells are known to first enter S-phase after trauma, indicating that it may be a primary r ather than a secondary response to injury. These results indicate that the SCA is a signaling molecule that may influence the potential of nonsensory supporting cells to either proliferate or differentiate into hair cells.