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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).
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