Figure 2.

Sustained BMP activity is critical for lens development. (a) Specification maps of gastrula stage chick embryos; lens (blue circles) and olfactory (orange circles) placodal progenitors are situated in the rostral neural plate border. (a,b) Blue/orange, green, orange and blue boxes indicate regions of explants. (a) Gastrula stage lens/olfactory explants (blue/orange box) generate cells of lens and olfactory character when cultured alone, and cells of neural character if cultured together with Noggin. Gastrula stage forebrain explants (green box) generate cells of lens and olfactory character when cultured together with BMP4. (b) Neural fold stage lens explants (blue box) generate cells of lens character when cultured alone, and cells of olfactory character if cultured together with Noggin. Neural fold stage olfactory explants (orange box) generate cells of lens character when cultured together with BMP4. Modified from [19]. E, epidermal; B, neural plate border; N, neural plate; NF, neural fold. See text for more details.