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Fig. 2. Bipolar differentiation of the midbrain roof plate.
(A-A'') BMP signaling is required for RP differentiation later
than stage HH10. Lateral (A), posterior (A') and dorsal (A'') views
of the same embryo fixed 2 days after insertion of a noggin-soaked bead in the
midbrain and labeled for Gdf7 transcripts. The midbrain RP is mostly
missing (A, arrowhead) except for a faint labeling at its caudal (A',
arrowhead) and rostral (A'', arrowhead) ends. (B,C) Local
and distant effects of FGF8 beads. Lateral views of embryos labeled for
Wnt1 2 days after implantation of FGF8 beads. In most cases, the
induced RP extends from the dorsal midline to the bead (B, arrowhead). In
cases where the FGF8 bead induces locally a small RP segment (C, arrow), a
small deflection of the endogenous RP also points in the direction of the bead
(C, arrowhead).