During larval stages, most Hox genes are broadly expressed in the ectoderm and developing VNC, largely share a common posterior boundary at the posterior growth zone, and have gene-specific anterior expression boundaries.
Furthermore, the patterning that we observe throughout the ectoderm generally corresponds to that of "head/anterior brain" patterning known for hemichordates and vertebrates, which share a common ancestor with the sea star.
The limbs of vertebrate animals emerge from the embryonic flank as buds of somatopleure-derived mesenchymal cells covered by an epithelial layer, the ectoderm, flattening into paddle shapes as they grow.
To further confirm the specificity of these treatments, we rescued the migration of Sdf1-Mo and Cxcr4-Mo-injected cells by respectively grafting a piece of ectoderm overexpressing Sdf1 or coinjecting Sdf1 mRNA in the ectoderm or Cxcr4 mRNA alongside the Morpholinos.
Nevertheless, this possibility was formally ruled out by a detailed analysis of Wnt family genes expressed by 10T1/2 fibroblasts, ectoderm and somite explants which revealed that none of the 84 genes tested was induced by EGF.
The caudal eminence has a bulb-like appearance and consists of a mass of loose mesenchyme covered by the ectoderm [ Fig. 4B; for a human description see O'Rahilly and Muller (O'Rahilly and Muller, 1989)].
Before this, cells pass initially through a primitive ectoderm (PE) stage, as shown by the expression of Fgf5 [20], [20], preceding the appearance of NP markers at day 3.
The vestibular canals are sculpted from the otic vesicle, a hollow ball of epithelial cells that is formed by invagination of ectoderm at the level of the hindbrain.
Outside the dentine is the enamel, secreted by the overlying ectoderm.
The gastrula consists of the archenteron lined by the digestive endoderm, surrounded by the locomotory ectoderm.
