IDENTIFICATION OF GENES EXPRESSED AFTER NOISE EXPOSURE IN THE CHICK BASILAR PAPILLA

We used differential display of mRNA, a method based on reverse transc riptase-PCR, to identify genes whose expression increases in response to acoustic trauma in the chick basilar papilla. Identifying these gen es would provide insight into processes involved in repair of the dama ged epithelium or in hair cell regeneration. We compared mRNA from the basilar papilla of normal chicks, from chicks exposed to an octave ba nd noise (center frequency: 1.5 kHz) presented at 118 dB for 6 h, and from chicks exposed to noise and allowed to recover for 2 days. Thus f ar, we have identified 70 bands that appear to be differentially displ ayed on DNA sequencing gels; approximately 40 of these bands have been subcloned and sequenced. DNA sequences were compared with sequences i n the GenBank database to identify genes with significant (70-85%) seq uence identity to known genes. Chick cDNAs identified included: the pa rathyroid hormone-related protein, an immediate early gene; the delta- subunit of the neuronal-specific Ca2+/calmodulin-regulated protein kin ase II; and the GTP-binding protein CDC42, a member of the ras superfa mily of G proteins. A fourth cDNA had 84% sequence identity to an unch aracterized human cDNA (expressed sequence tag), indicating that this is a novel gene. Slot-blot hybridization analysis of these cDNAs probe d with labeled DNA generated from mRNA from each experimental group in dicated higher levels of mRNA for each of these four genes after noise exposure. These results indicate the potential involvement of both Ca 2+/calmodulin-mediated signaling and GTPase cascades in the response t o noise damage and during hair cell regeneration in the chick basilar papilla.