Figure 2.

mbl^−/− embryos harbor a mutation in the axin1 gene. (A) Mapping of mbl on linkage group 3 close to axin1 on the corresponding region of a radiation hybrid map. (B) Schematic representation of the Axin1 protein showing the amino-acid exchange (L³⁹⁹→Q) and underlying point mutation (T→A) within the predicted Gsk3 binding site in the mbl Axin1 allele. (C–F) Localization of axin1 transcripts in lateral (D,E) and animal pole (C,F) views of wild-type embryos at the 1 6 cell stage (C), sphere stage (D), 80% epiboly (E) and bud stage (F). axin1 transcripts are maternally provided and ubiquitously expressed in wild-type embryos. (G–L) Phenotypes of wild-type (G,J), mbl^−/− (H,K), and mbl^−/− embryos injected with axin1 RNA (I,L) stained for the expression of flh in the epiphysial region of the diencephalon (arrow,G) at bud stage (G–I) or stained with α-acetylated tubulin antibody at pharyngula stage (J–L). Injection of axin1 RNA at the one-cell-stage rescues the mbl^−/− mutant phenotype determined by the pattern of flh expression at bud stage and the presence of telencephalon (asterisks) and eyes (arrowheads) at pharyngula stage.