Fig 4. Expression in S. kowalevskii of Orthologs of Chordate Genes Important in Dorsoventral Patterning of the Neural Tube.

All embryos are shown as optical sections, and oriented in a similar manner as in Figure 2 with anterior to the top and left of each panel and dorsal in the top right of each panel, unless otherwise specified. (A) Hh expression in the apical tip of a day 3 embryo, and (B) at day 5 at the same location. (C) Endodermal expression of nk2–2 (also called nkx2.2) in the late gastrula, with a sharp delineation between presumptive proboscis mesoderm and definitive endoderm, and with reduced expression in the posterior endoderm, and (D) endodermal expression of nk2-2 at day 3.5, with left-right lateral patches in the pharyngeal endoderm ventral to the site of gill pore formation and with expression down-regulated in other regions of the endoderm. (E) Expression of msx in the late gastrula, and (F) at day 3. Expression occurs exclusively in the ectoderm of the metasome and is down-regulated in the telotroch, the cilated band, as marked (white arrowhead).