4.4 Article

Ablation studies on the developing inner ear reveal a propensity for mirror duplications

Journal

DEVELOPMENTAL DYNAMICS
Volume 236, Issue 5, Pages 1237-1248

Publisher

WILEY
DOI: 10.1002/dvdy.21144

Keywords

enantiomorph; Xenopus; regeneration; inner ear; hedgehog; placode; otocyst; mirror image; hair cell; organogenesis

Funding

  1. NIDCD NIH HHS [R01 DC004061] Funding Source: Medline

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The inner ear develops from a simple ectodermal thickening known as the otic placode. Classic embryological manipulations rotating the prospective placode tissue found that the anteroposterior axis was determined before the dorsoventral axis. A small percentage of such rotations also resulted in the formation of mirror duplicated ears, or enantiomorphs. We demonstrate a different embryological manipulation in the frog Xenopus: the physical removal or ablation of either the anterior or posterior half of the placode, which results in an even higher percentage of mirror image ears. Removal of the posterior half results in mirror anterior duplications, whereas removal of the anterior half results in mirror posterior duplications. In contrast, complete extirpation results in more variable phenotypes but never mirror duplications. By the time the otocyst separates from the surface ectoderm, complete extirpation results in no regeneration. To test for a dosage response, differing amounts of the placode or otocyst were ablated. Removal of one third of the placode resulted in normal ears, whereas two-thirds ablations resulted in abnormal ears, including mirror duplications. Recent studies in zebrafish have demonstrated a role for the hedgehog (Hh) signaling pathway in anteroposterior patterning of the developing ear. We have used overexpression of Hedgehog interacting protein (Hip) to block Hh signaling and find that this strategy resulted in mirror duplications of anterior structures, consistent with the results in zebrafish. Developmental Dynamics 236.-1237-1248, 2007. (C) 2007 Wiley-Liss, Inc.

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