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Fig. 1
At the shield stage, the PPR cells have distinct preference to adopt the otic fate along the A-P axis. A: A diagram of animal pole view of a shield stage embryo (6 hpf) (adopted from Streit, Kozlowski et al., 1997). It illustrates the neural ectoderm (grey shaded area), the preplacodal region (the partially overlapped color-areas between two black lines), which could be presumptively called the PPR and pointed by an arrow, and the belly ectoderm (pink shaded area). The red arrow indicates where Fgf8 soaked beads (circled asterisks) are implanted. Cells of the colored areas give rise to distinct placodal fates (indicated in A). B: An Fgf8 bead is implanted in the presumptive PPR. Arrowhead indicates the shield. The scale bar does not apply. C: An Fgf8 bead implanted into the presumptive PPR (intermediate) induces ectopic ear (blue arrow) as indicated by cldna expression. A black arrow indicates the endogenous ear. D: The endogenous ear fails to form in an fgf8-/- mutant injected with fgf3MO (black arrow), but implantation of an Fgf8 bead induces an ectopic ear (blue arrow in the inlet) in the intermediate PPR. E: Ectopic ear (blue arrow) is induced caudally to the endogenous ear (black arrow) by an Fgf8 bead implanted in the posterior PPR. F: Percentage of Fgf8-beads that induce ectopic ears in the anterior (beads anterior to endogenous eyes, aPPR), intermediate (beads between endogenous eyes and ears, iPPR) and posterior (beads caudal to endogenous ears, pPPR) implants. G: An Fgf8 bead implanted just outside the presumptive PPR induces a pair of ectopic ears (blue arrows). One of the ectopic ears is seen fused to the endogenous ear (black arrow). H: An Fgf8 bead implanted in the anterior neural ectoderm fails to induce any cldna expression. The black arrow points to the endogenous otic placode. Unless indicated at the lower left corner of each panel, all are the wild-type embryos. A,B: Animal pole views. C–E and G,H: Side views with anterior to the left. A,B: 6 hpf; C: 36 hpf; D–G: 24 hpf; H: 14.5 hpf. Scale bar = 200 µm in D,E, G,H; 50 µm in C.