Fig. 3. Cell-autonomous defect of convergent extension in the Lp mutant as demonstrated in chimeras. (A-C) +/+ +/+ and (D-F) +/+ Lp/Lp chimeras at E8, produced by injecting wild-type ES cells into Lp blastocysts that are also homozygous for the ROSA26 ß-gal marker. After X-Gal staining and Eosin counterstaining, all blastocyst-derived cells are blue, while ES-derived cells are pink. Sections at the level of the notochordal plate (A,D), mid-trunk neural folds (B,E) and cranial neural folds (C,F) all show an apparently random admixture of blue and pink cells in +/+ +/+ chimeras (A-C) whereas +/+ Lp/Lp chimeras (D-F) exhibit increased numbers of pink (wild-type) cells in the midline of both neural plate (arrows) and notochordal plate (asterisk in D). More lateral regions show a more even mixture of blue and pink cells. Inset: low magnification view of +/+ Lp/+ chimera showing boxed areas in which cell counts were made. (G) Quantitative analysis of relative cell numbers in midline and lateral neural plate regions of different chimera genotypes. Difference in % ß-gal-negative (i.e. wild-type) cells between midline and lateral regions gives values close to zero at all axial levels of +/+ +/+ chimeras whereas +/+ Lp/Lp chimeras show values deviating markedly from zero along the entire body axis. +/+ Lp/+ chimeras show a wide range of values, encompassing the extremes of the other two genotypes. Scale bar: in A, 0.05 mm for A-F.