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Fig. 7 Tectal cell death in apc mutants is not caused by ectopic Fgf8 signalling. All embryos at 48 hpf (A, B, E–N) Dorsal view, anterior to the left. (C–D;O–P) Transversal sections of the midbrain, dorsal up. (A, B) Transmission images showing the collapsed ventricles (asterisk) and the opaque tectum (arrowhead) in apc mutants (B). Dashed lines indicate OT outline, MHB, cerebellum and otic vesicle. otx2 (C, D) and emx2 (C′, D′) expression in optic tectum of apc mutants (D, D′) is abolished. Note the reduction in tectal tissue in mutants. Dashed line indicates dorsal/ventral midbrain boundary. (E–H) Tunel assay shows that blocking ectopic Fgf8 signalling by 8 μM SU5402 treatment (G, H) does not rescue cell death in the mutant tectum (H). (I–L) otx2 expression is mainly unaltered in wild-type (K) and mutant embryos (L) upon SU5402 treatment. Dashed lines indicate OT outline. (M, N) Tectum and MHB morphology of apc embryo at 48 hpf with wild-type cells transplanted into MHB is similar to untransplanted apc embryo (compare to A, B). (N) Overlay with fluorescence to show location of transplanted wild-type cells (green) in MHB (right panel — magnification of boxed area). Dashed lines indicate the MHB and cerebellum. (O–P) Transverse sections of mutant embryos with transplanted WT cells (brown), stained for otx2 (blue). otx2 is restored in wild-type cells transplanted into apc mutant tectum (boxes in panels O, O′ magnified in panels P, P′. Arrowheads indicate single transplanted cells. Dashed line indicates dorsal/ventral midbrain boundary. ce, cerebellum; ot, optic tectum; vm, ventral midbrain. Scale bar 125 μm.
Reprinted from Developmental Biology, 331(2), Paridaen, J.T., Danesin, C., Elas, A.T., van de Water, S., Houart, C., and Zivkovic, D., Apc1 is required for maintenance of local brain organizers and dorsal midbrain survival, 101-112, Copyright (2009) with permission from Elsevier. Full text @ Dev. Biol.