Fig. 6. Dynamic expression of LvTbx2/3 in the skeletogenic mesenchyme cells (PMCs). (A) Expression in PMCs begins at mid-late gastrula stage in all PMCs. (B,C) Two views of the same early-prism stage embryo. (B) Superficial view of the PMCs under the ectoderm. At this stage, asymmetric distribution of LvTbx2/3 is observed in the PMC lineage. (C) Deeper, cross-sectional view of the embryo in B co-stained for LvTbx2/3 (red) and EctoV (green). LvTbx2/3 localization in PMCs is in the aboral territory of the embryo. Note the clear, asymmetric distribution in the endoderm. (D) An oblique view of a late prism-stage embryo stained for LvTbx2/3 (red) and 5a7 (green). Distribution of LvTbx2/3 protein is limited to the aboral PMCs and is not present in the ventrolateral clusters that have begun to form triradiate spicules. Animal (E) and vegetal (F) cross-sectional views of early-pluteus stage embryos. LvTbx2/3 protein persists in the aboral PMCs and is not observed in the oral PMCs.