Fig. 5. LvTbx2/3 protein is asymmetric throughout embryonic development. Cross-section images (A,C,E,G,I,K) and surface projections (B,D,F,H,J). LvTbx2/3 expression first appears at the mesenchyme blastula stage and is distributed asymmetrically in the presumptive endoderm and ectoderm, as viewed in cross-section (A) and in a vegetal-surface view (B). Early-gastrula stage embryos in cross-section (C) and a vegetal view (D) maintain asymmetric distribution of LvTbx2/3 in the presumptive endoderm and ectoderm, whereas the endoderm and mesoderm that have invaginated into the blastocoel do not express protein. (E,F) Mid-gastrula stage embryo (cross-section and surface projection of the same embryo). LvTbx2/3 expression is maintained asymmetrically in the presumptive endoderm and ectoderm and is not present in invaginated endoderm or mesoderm. (G,H) Late gastrula distribution of LvTbx2/3 protein (cross-section and surface projection of the same embryo). Asymmetric expression is observed in the invaginated endoderm, the ectoderm and in all of the skeletogenic mesenchyme cells at this stage (also see Fig. 6). (I) Animal view of early pluteus embryo optically sectioned to remove the most superficial layers of ectoderm and expose the archenteron and stomodaeum. LvTbx2/3 is distributed asymmetrically in the surface ectoderm and the length of the archenteron. (J) Vegetal surface view. Distribution of LvTbx2/3 protein is asymmetric in the aboral ectoderm nuclei. High concentrations of LvTbx2/3 are also observed in the distal most nuclei of the extending pluteus arms. (K) Vegetal cross-section of a late pluteus embryo. Asymmetric distribution is maintained in cells of the ectoderm, endoderm and skeletogenic mesoderm.