IDENTIFICATION OF PREFERENTIALLY EXPRESSED COCHLEAR GENES BY SYSTEMATIC SEQUENCING OF A RAT COCHLEA CDNA LIBRARY

107 expressed sequence tags (ESTs) from a rat cochlea cDNA Library wer e identified by systematic sequencing coupled to database selection an d RT-PCR analysis of novel sequences. This approach led us to select a clone, pCO8, showing no significant homology with any database sequen ce, that corresponds to a mRNA whose expression is restricted to the c ochlea, except for traces detected in brain. Additional clones with no vel sequences enriched in the cochlea were also found. ESTs bearing si gnificant homologies with database sequences (63 out of 107) were clas sified according to the putatively encoded protein. They include tissu e-specific genes not previously described in the cochlea as well as kn own genes from other species. We performed in situ hybridization in co chlear tissues to localize the pCO8 mRNA and that of clone pCO6 which is 100% homologous to the delayed rectifier potassium channel drk1. We found that both mRNAs were exclusively expressed in the cellular body of the primary auditory neurons from the spiral ganglion of the cochl ea. These results indicate that this approach is an efficient way to i dentify novel genes that could be of importance in cochlear function. (C) 1997 Elsevier Science B.V. All rights reserved.