Figure 2. Requirements for otic induction from primitive ectoderm.
The figure depicts a consensus scheme of otic induction for amniotes. For each step, the necessary signaling factors for the otic pathway are shown. The alternative pathway is chosen in the absence of the specific combination of signaling and/or with additional signals. Gene expression defining tissue identity for individual steps are indicated. X represents the requirement for an inhibitor of a signaling pathway, such as BMP or Wnt inhibitors.