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Fig. 3. Fgf signalling is required for the initiation of heart specification. Expression of both nkx2.5 and isl1 is readily detectable in the cardiac crescent of stage 20 embryos (A and C). Embryos treated with SU5402 to inhibit fgfr1 activity show a loss of nkx2.5 expression (B), and a down regulation of isl1 expression (D). In both cases, the anterior pole of the embryo is viewed, with dorsal folds visible toward the top of the image. The total number of embryos examined for each panel is indicated in the lower left hand corner. |
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Fig. 8. Retinoic acid and fgf are opposing signalling molecules in patterning the LPM. Embryos were treated at stage 12 with either RA, SU5402 or both RA and SU5402 and assayed by whole mount in situ hybridization for expression of nkx2.5 (arrowhead a), isl1 (arrowhead b) and foxf1. Treating embryos with RA reduces the expression domain of both nkx2.5 (B) and isl1 (F) compared with controls (A and E). Significantly reduced domains of nkx2.5 and isl1 were also present in SU5402 treated embryos (C), however when embryos are treated with both RA and SU5402 neither marker is detectable (D and H). The expression domain of foxf1 was expanded in both the RA (J) and SU5402 (K) treatments when compared to controls (I), however when embryos were treated with both RA and SU5402, foxf1 expression was detectible across the entire LPM although expression was still graded. Ant: anterior view with dorsal at top of image. Pos: posterior view with dorsal at top of image. Llv is left lateral view. The total number of embryos examined for each panel is indicated in the lower left hand corner. |
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Fig. 9. Loss of retinoic acid signalling partially rescues effects of loss of Fgf signalling on the domains of isl1 and Xbra. Decreasing RA signalling in SU5402 treated embryos had little effect on the nkx2.5 domain (D) as it was still present in a highly restricted domain similar to the SU5402 treatment (C). However, a loss of Fgf signalling leads to a loss of isl1 (H) and Xbra (T), while neither domain is changed when RA signalling is lost (F and R). However, when Fgf signalling is decreased in conjunction with reduced RA signalling both isl1 and Xbra expression is detectable in their normal domains (H and T). However, the restriction of the hand1 expression domain under reduced RA condition (J and N) seems to be dominant to the extended domain seen in the SU5402 treated embryos (K and O) as losing both RA and Fgf signalling (L) leads to a restricted domain similar to the RA antagonist alone.
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Fig. 4. Fgf signalling is necessary for heart patterning and morphogenesis. Embryos were treated with SU5402 during different developmental windows to determine when Fgf signalling is necessary for heart development and assayed for expression of nkx2.5 (A–D and I–L) or tnni3 (E–H and M–P). Fgf signalling was inhibited at successively later stages (top panel: A–H) and compared to control embryos (A and E). Embryos treated with SU5402 at either stage 12.5 (B and F) or stage 20 (C and G) demonstrate a complete loss of heart marker expression by stage 32, while embryos treated at stage 24 (D and H) show expression of both nkx2.5 and tnni3 but no discernable heart tube. Fgf signalling was also inhibited at stage 12.5 and restored at later stages by removing the inhibitor (bottom panel: I–P) and compared to control embryos (I and M). When Fgf signalling is restored by either stage 20 (J and N) or stage 22 (K and O), both heart markers are expressed however a normal heart tube is not formed. If signalling is not restored until stage 26 (L and P), neither nkx2.5 or tnni3 are detectable. White arrows mark the heart region. The total number of embryos examined for each panel is indicated in the lower left hand corner. |
