Figure 4

Sensory epithelium fails to develop in absence of BMP signaling. (A,B) Blockade of BMP signaling with 0.5 μg/ml noggin robustly decreased the number of hair cell antigen-expressing hair cells (HCA shown in red) that were detectable after seven days in culture. It appears that Pax-2 expression (shown in green) is not affected by noggin. (C,D) In noggin-treated otocysts, islet-1-positive sensory epithelia (visualized in green) were evidently diminished, but not completely absent (arrowheads), as shown in this representative set of images. The images shown are not representative for the neural domains where we observed that the overall number of islet-1-positive neurons (arrows in C and D) did not differ between noggin-treated and control otocysts (no significant difference, n = 5). The inset in (C) shows a higher magnification of the islet-1-positive sensory epithelia (see also Li et al., 2004b).