1: J Neurocytol. 1999 Oct-Nov;28(10-11):795-807. 

Expression of Pax2 and patterning of the chick inner ear.

Hutson MR, Lewis JE, Nguyen-Luu D, Lindberg KH, Barald KF.

Department of Cell and Developmental Biology, The University of Michigan Medical
School, Ann Arbor Michigan 48109, USA.

Early regionalized gene expression patterns within the otocyst appear to
correlate with and contribute to development of mature otic structures. In the
chick, the transcription factor Pax2 becomes restricted to the dorsal and entire
medial side of the otocyst by stage 16/17. The dorsal region of the otocyst
forms the endolymphatic duct and sac (ED/ES), and the cochlear duct is derived
from the ventromedial region. In the mouse, however, Pax2 expression is reported
only in the ventromedial and not the dorsal otocyst. In Pax2 null mice, the
cochlea is missing or truncated, but vestibular structures differentiate
normally. Here we demonstrate that in the chick, the emerging ED/ES express high
levels of Pax2 even when the position of the emerging ED is altered with respect
to its environment, either by 180 degrees otocyst rotations about the
anterior/posterior axis or transplantation of the otocyst into the hindbrain
cavity. However, the Pax2 expression pattern is plastic in the rest of the otic
epithelium after 180 degrees rotation of the otocyst. Pax2 is upregulated on the
medial side (formerly lateral), and downregulated on the lateral side (formerly
medial and expressing Pax2) indicating that Pax2 expression is influenced by the
environment. Although Pax2 is upregulated in the epithelium after 180 degrees
rotations in the region that should form the cochlear duct, cochlear ducts are
truncated or absent, and the ED/ES emerge in a new ventrolateral position.
Ablation of the hindbrain at the placode or early otic pit stage alters the
timing of regionalized Pax2 expression in the otocyst. The resulting otocysts
and ears are generally smaller, vestibular structures are abnormal, ED/ES are
missing but cochlear ducts are of normal length. The hindbrain and dorsal
periotic mesenchyme provide unique trophic and patterning information to the
dorsal otocyst. Our results demonstrate that the ED is the earliest structure
patterned in the inner ear and that the hindbrain is important for its
specification. We also show that, although normal Pax2 expression is required
for cochlear duct development, it is downstream of ventral otocyst patterning
events.

PMID: 10900085 [PubMed - indexed for MEDLINE]


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