A model of ventral otic patterning in the zebrafish.

<p>(A,B) At otic placode stages, FGF3 from the hindbrain patterns anterior otic regions, while RA signalling is required for the expression of <i>tbx1</i> and subsequent non-neural development (based on <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1004858#pgen.1004858-Radosevic1" target="_blank">[2]</a>, <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1004858#pgen.1004858-Hammond2" target="_blank">[12]</a>. (C–E) At OV stages, FGF and RA signalling pathway members contribute to maintenance of otic patterning. It is likely that both otic and pharyngeal <i>fgf3</i> expression sources influence otic patterning, although our experiments have not distinguished these. In addition, expression of <i>otx1b</i> in the OV starts from around 18S. (F) FGF signalling is required for the expression of <i>aldh1a3</i> and <i>otx1b</i> in the OV. (G) Cells expressing <i>aldh1a3</i> in the OV itself provide a local source of RA. RA signalling acts in a negative feedback loop to restrict <i>fgf</i>-expressing cells anteriorly. In addition, RA signalling prevents <i>otx1b</i> expression from spreading into anteroventral neurogenic regions of the OV and promotes the maturation of otic neuroblasts. Abbreviations: a, anterior otic placode; hb, hindbrain.