Fig. 6. BMP family members and RP autoinduction. Whole embryos treated for the detection of Gdf7 transcripts (A,D,E,G,H) or WNT1 (purple) and TTR (black) (B,C) 3 (A), 5 (B,B',C,C') and 1 (D-I) day(s) after implantation of beads soaked in BMP7, noggin, GDF7 or a mixture of GDF7+FGF8 recombinant proteins (see color code). Dorsal (A-C) or posterior (D,E,G,H) views. (B',C') Transverse sections through B and C, respectively. The inset in B' shows a comparable section through a control embryo. (F,I) Longitudinal sections through the midbrain of embryos similar to D and G, respectively. The sections were immunostained for active caspase 3 (^*caspase). (A,B,B') BMP7 beads did not induce RP markers locally. They affected RP patterning on the host midline, inducing the formation of a sheet of cells between the two widened Gdf7 (A) or Wnt1 (B,B') positive RP halves. This cell sheet expressed neither the roof-plate marker WNT1 nor the choroid plexus marker TTR (B,B'). (C,C') Noggin beads induced the formation of a dome-shaped tectum that lacked both WNT1 and TTR expression. (D,E; 13/16) GDF7 beads induced Gdf7 expression in a cell patch isolated from the midline (D) or through widening the midline Gdf7 domain (E). Cell death was not markedly increased by GDF7 overexpression: ^*caspase immunoreactive cells were barely detectable (F, a single immunoreactive cell at most per section in one out of five embryos). Beads releasing GDF7 and FGF8 together induced a widely scattered expression of Gdf7 (G,H) and impaired the condensation of Gdf7 expression into the characteristic structure of the FGF8-induced ectopic RP. Cell death was increased near the midline (I) in all cases (7/7, at least three sections containing more than four ^*caspase immunoreactive cells).