Hi all -
I have a general question about induction of otic vesicles in
amphibia. It appears that all vertebrates (at least that I've seen)
have the otic vesicle adjacent to rhombomere 5 of the hindbrain. This
includes mouse, chick, and zebrafish. In contrast the Xenopus otic
vesicle lies more anteriorly, adjacent to rhombomeres 3/4. Is this
generally true of amphibia? or is Xenopus unique? Is there an
evolutionary basis for this difference?
This difference suggests that the inductive capacity of the hindbrain is
different along the A/P axis in Xenopus relative to other vertebrates.
It has been suggested that fgf3 plays a role in ear induction, and it
has been shown that fgf3 expression in Xenopus is adjascent to the
otocyst (D. Tannahill, H. V. Isaacs, M. J. Close, G. Peters & J. M.
Slack. Development 115: 695-702 (1992)). This suggests to me that there
may be some initial difference in the patterning of the Xenopus
hindbrain relative to other vertebrates.
Does anyone have any thoughts on the issue?
kolm at wi.mit.edu