Figure 5

Prevention of the contact between r4 and its boundaries results in sustained FGF3 expression in r4. (A-C): Diagram and photographs of embryos with a unilateral slit between r4 and the r3/r4 boundary (B, arrow) and insertion of a barrier into the gap (A, C arrows) in 12ss embryos. (D-H): Flat-mounted hindbrains of in situ hybridized embryos stained for FGF3 at 28 ss. FGF3 remains expressed in r4 following insertion of a non-permeable barrier between r4 and r3/r4 boundary (D, E) or r4/r5 boundary (F) (asterisks), compared to the absence of FGF3 in r4 of the contra-lateral side. Barrier insertion between r3 and r3/4 boundary reveals no effect on FGF3 expression in either r3 or r4 (G, asterisk). Insertion of a permeable membrane between r3/r4 boundary and r4 results in FGF3 downregulation from r4 (H). (I): Flat-mounted hindbrain in situ hybridized with follistatin probe at 36 ss. Follistatin is expressed at higher levels in r4 following insertion of a non-permeable barrier between r4 and the r3/r4 boundary (I, asterisk), compared to the control side. In all images, anterior is at the top, grey lines and black arrows mark the barrier position, and r4 is marked.