Fig. 4

Ct-msi is broadly expressed in the developing brain and VNC. a–q Ct-msi transcripts were detected across stages 3–6 using WMISH. Images are to the same scale as in Figs. 2 and 3. Arrows in panels (a) and (b) indicate Ct-msi expression in the anterior neuroectoderm, while arrowheads indicate Ct-msi ⁺ cells around the blastopore. White arrowheads in panels (g), (h), (k), and (m) indicate expression in the mesoderm. Black arrowheads in (m) and (h) indicate expression in the presumptive VNC. Arrows in (i) and (m) indicate expression near the circumesophageal connectives. The white arrowhead in the inset in (q) indicates a longitudinal row of Ct-msi ⁺ cells positioned between the mesoderm and endoderm. In each panel, the stage of the animal is indicated in the lower left, and the view is indicated in the lower right (lat lateral, vlat ventrolateral, vent ventral, ant anterior). In all lateral and ventrolateral views, anterior is to the left and ventral down; in all ventral views, anterior is to the left; and in all anterior views, ventral is down. Panels (f), (j), and (o) are cropped images of the episphere from a ventral view. Panel (l) is a cropped image of the episphere from a ventrolateral view. Panels (k) and (p) are cropped images of the trunk. An asterisk marks the position of the mouth, and the prototroch (pt) and telotroch (tt) are labeled with dashes. In (j) the prototroch is denoted with a dash. STBP, stage 3 blastopore; ST3mo, stage 3 mouth