Fig. 6.

Lineage tracing in Tbx6 homozygous mutant embryos of a cohort of cells that expressed Tbx6-creERT2 between E6.5 and E7. Cre-reporter females heterozygous for a Tbx6 null allele were crossed with Tbx6 heterozygous males and were injected with tamoxifen at E6.5; embryos were recovered at E9.5 and stained for lacZ. (A-C) Whole-mount embryos of different developmental stages with lacZ-positive cells in the head region (arrows in B,C), in the irregular anterior somites, in the trunk corresponding to the ectopic neural tubes characteristic of the Tbx6 homozygous phenotype and in the expanded tail bud. The exaggerated twisting of the torso is a feature of the mutant phenotype. (D-H) Representative transverse sections showing lacZ-positive cells in the head mesenchyme (D,E), heart (E), ectopic neural tubes (F-H), notochord (1/7 embryos; arrow in F), lateral body wall (G), mesenchyme surrounding the gut (G) and throughout the mesenchyme of the expanded tail bud (H). ba, branchial arch; bp, branchial pouch; da, dorsal aorta; ec nt, ectopic neural tube; g, gut; h, heart; hg, hindgut; lbw, lateral body wall; nt, neural tube; p, pharynx; tb, tailbud. Scale bars: 100 μm.