Gene discovery in the auditory system: characterization of additional cochlear-expressed sequences.

To identify genes involved in hearing, 8494 expressed sequence tags (ESTs) were generated from a human fetal cochlear cDNA library in two distinct sequencing projects. Analysis of the first set of 4304 ESTs revealed clones representing 517 known human genes, 41 mammalian genes not previously detected in human tissues, 487 ESTs from other human tissues, and 541 cochlear-specific ESTs (http://hearing.bwh.harvard.edu). We now report results of a DNA sequence similarity (BLAST) analysis of an additional 4190 cochlear ESTs and a comparison to the first set. Among the 4190 new cochlear ESTs, 959 known human genes were identified; 594 were found only among the new ESTs and 365 were found among ESTs from both sequencing projects. COL1A2 was the most abundant transcript among both sets of ESTs, followed in order by COL3A1, SPARC, EEFY1A1, and TPTI. An additional 22 human homologs of known nonhuman mammalian genes and 1595 clusters of ESTs, of which 333 are cochlear-specific, were identified among the new cochlear ESTs. Map positions were determined for 373 of the new cochlear ESTs and revealed 318 additional loci. Forty-nine of the mapped ESTs are located within the genetic interval of 23 deafness loci. Reanalysis of unassigned ESTs from the prior study revealed 338 additional known human genes. The total number of known human genes identified from 8494 cochlear ESTs is 1449 and is represented by 4040 ESTs. Among the known human genes are 14 deafness-associated genes, including GJB2 (connexin 26) and KVLQT1. The total number of nonhuman mammalian genes identified is 43 and is represented by 58 ESTs. The total number of ESTs without sequence similarity to known genes is 4055. Of these, 778 also do not have sequence similarity to any other ESTs, are categorized into 700 clusters, and may represent genes uniquely or preferentially expressed in the cochlea. Identification of additional known genes, ESTs, and cochlear-specific ESTs provides new candidate genes for both syndromic and nonsyndromic deafness disorders.