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Fig. 8. Individual role of Wnt and FGF signaling in the positioning of the
wavefront. (A) RT-PCR analysis of dorsal explants treated with
SU5402 or WIF1. Dorsal explants were dissected at stage 14 from the normal
embryos and cultured for 1.5 or 3 hours with 0.1% BSA in LCMR containing
SU5402 or WIF1. (B) Western blot analysis of MAPK phosphorylation. The
dorsal explants were treated with the indicated drug/protein for 1.5 or 3
hours. MAPK phosphorylation was analyzed by anti-dp-ERK Ab (upper panel) and
total MAPK by anti-ERK Ab (lower panel). MAPK phosphorylation was reduced by
1.5-3 hours of SU5402 treatment (lanes 2, 5) or 3 hours of WIF1 treatment
(lanes 3, 6). (C-C'') Whole-mount in situ hybridization of
Arp-A probe. The dorsal explants were isolated from the neural stage
normal embryos and treated with SU5402 (C') or with WIF1 (C'') for
1.5 hours. Reduced Arp-A expression; BSA, 0/20; SU5402, 0/20; WIF1,
14/20. (D-D'') Wholemount in situ hybridization of Thy1
probe. The dorsal explants of the stage 14 normal embryos were treated with
SU5402 (D') or with WIF1 (D'') for 1.5 hours. Upper and lower
dashed line indicates S-II/Thy1 and S-III/Thy1 stripes,
respectively. (E) Bar graph shows the effect of SU5402, WIF1 and
SU5402/WIF1 treatment on the relative distance between S-II/Thy1 and
S-III stripes. Gray bar and black dots indicate the average distance and
individual distance, respectively. Data are represented as fold change,
compared with the average distance of BSA/DMSO-treated explants (=1.0).
(F) Summary of the role of Shisa2 in segmentation. The caudorostrally
decreasing gradients of Wnt and FGF signal control the maturation of PSM and
determine the position where cells transit to the definitive segmental fate
(TP: transition point). Shisa2 is expressed strongly in the region
covering the TP, but its expression gradually decreases in the caudal PSM.
Shisa2 positions the TP by the individual inhibition of the Wnt and FGF
signaling. RA positions the TP at least in part by the indirect inhibition of
FGF signaling.
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