Expression of Ntl protein in ntl mutant embryos. (A-D) Immunostaining of wild-type (A,C), ntl^b160 (B), and ntl^b195 (D) embryos. (A,B) Vegetal pole view of 95% epiboly embryos. (C,D) Posterior trunk and tail region of 20-hour old embryos. Ntl protein was not detectable in whole-mount antibody preparations of mutant embryos.

Expression of ntl RNA in ntl mutant embryos. (A-D) Whole-mount in situ hybridizations detecting ntl mRNA. (A) Mutant ntl^b160 embryos (two embryos on the left) at the embryonic shield stage exhibit reduced levels of ntl transcript if compared to sibling embryos (two embryos on the right). Mutant embryos were identified by their lack of Ntl protein after antibody stainings. (B) Wild-type sibling of embryo shown in (C) at 100% epiboly. There is strong expression of ntl RNA in the axial mesoderm and the germ ring. (C) Mutant ntl^b195 embryo at 95% epiboly. Transcript levels are high in the germ ring, but hardly detectable in the presumptive notochord (arrowhead). Note the staining of dorsal marginal cells (see text for details). (D) Mutant ntl^b160 embryo at tailbud stage (10h), demonstrating that mutant embryos of both alleles behave indistinguishably with respect to ntl mRNA expression in cells of the presumprive notochord (arrowhead).