Biology Reference
In-Depth Information
FIGURE 5.11. Ideogram of human chromosome
3, showing the loci of four human hearing dis-
orders for which the responsible genes remain
to be identified: DFNB6 , DFNA18 , DFNB15 ,
and Usher syndrome type 3. Arrows indicate
the approximate positions of human cochlear
expressed sequence tags (ESTs) (Skvorak et al.
1999) that map to chromosome 3. Map loca-
tions for these and additional cochlear ESTs
can be found at http://hearing.bwh.harvard.edu .
libraries from these animals' inner ears are directly useful for investigating
genes involved in hearing and hearing loss in these animals. In several cases,
the human orthologs of genes first identified in mouse have been shown to
cause hearing loss in humans. Second, although rodent and bird cochleae
are small and difficult to dissect, there is a plentiful supply and the tissue
can be dissected immediately after the animal is sacrificed. This is in stark
contrast to human cochlear tissue, which is extremely difficult to obtain and
is often partially degraded due to postmortem autolysis.
The rodent and chick cochlear cDNA libraries that have been con-
structed to date have mostly been made in an effort to isolate genes that
are uniquely expressed in the inner ear. The first reported was a guinea pig
organ of Corti cDNA library (Wilcox and Fex 1992). Since then, at least
four rat inner ear libraries have been described, including one from mRNA
extracted exclusively from outer hair cells (Harter et al. 1999). The remain-
der were made from whole cochleae (Ryan et al. 1993; Beisel and Kennedy
1994; Soto-Prior et al. 1997). In each case, several hundred cochleae were
used as starting material. Two chicken cochlear cDNA libraries have been
Search WWH ::




Custom Search