Embryological manipulations in the developing Xenopus inner ear reveal an intrinsic role for Wnt signaling in dorsal–ventral patterning

Background: The inner ear develops from an ectodermal thickening known as the otic placode into a complex structure that is asymmetrical along both the anterior–posterior (A-P) and dorsal–ventral (D-V) axes. Embryological manipulations in Xenopus allow us to test regenerative potential along specific axes and timing of axis determination. We explore the role of Wnt signaling with gain and loss of function experiments. Results: In contrast to A or P half ablations, D or V half ablations almost never result in mirror duplications or normal ears. Instead there is a loss of structures, especially those associated with the ablated region. Rotation experiments inverting the D-V axis reveal that it is determined by stage 24–26 which is just before expression of the dorsal otic marker Wnt3a. Conditional blocking of canonical Wnt signaling results in reductions in the number of sensory organs and semicircular canals which could be placed in one of three categories, the most common phenotypes being similar to those seen after dorsal ablations. Conclusions: There is less regenerative potential along the D-V axis. Wnt3a protein alone is sufficient to rescue the severe loss of inner ear structures resulting from dorsal but not ventral half ablations