A. Rusch et al., Thyroid hormone receptor beta-dependent expression of a potassium conductance in inner hair cells at the onset of hearing, P NAS US, 95(26), 1998, pp. 15758-15762
Citations number
39
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
To elucidate the role of thyroid hormone receptors (TRs) alpha 1 and beta i
n the development of hearing, cochlear functions have been investigated in
mice lacking TR alpha 1 or TR beta. TRs are ligand-dependent transcription
factors expressed in the developing organ of Corti, and loss of TR beta is
known to impair hearing in mice and in humans. Here, TR alpha 1-deficient (
TR alpha 1(-/-)) mice are shown to display a normal auditory-evoked brainst
em response, indicating that only TR beta, and not TR alpha 1, is essential
for hearing. Because cochlear morphology was normal in TR beta(-/-) mice,
we postulated that TR beta regulates functional rather than morphological d
evelopment of the cochlea. At the onset of hearing, inner hair cells (IHCs)
in wild-type mice express a fast-activating potassium conductance, I-K,I-f
,I- that transforms the immature MC from a regenerative, spiking pacemaker
to a high-frequency signal transmitter. Expression of I-K,I-f was significa
ntly retarded in TR beta(-/-) mice, whereas the development of the endococh
lear potential and other cochlear functions, including mechano-electrical t
ransduction in hair cells, progressed normally. TR alpha 1(-/-) mice expres
sed I-K,I-f normally, in accord with their normal auditory evoked brainstem
response. These results establish that the physiological differentiation o
f IHCs depends on a TR beta-mediated pathway. When defective, this may cont
ribute to deafness in congenital thyroid diseases.