Fig. 3

Expression of Ciona intestinalis TCF/Lef. In situ hybridization of Ci-TCF/Lef mRNA. Expression begins in mesenchymal and neural plate cells (a, e), before becoming more widespread in the neural plate (white arrow heads) and head/lateral trunk mesenchyme (black double arrowheads) (b, c, d, f, g, h), with possibly some staining also in the endoderm (g, h). In tailbud stages staining becomes more refined in the head/lateral trunk mesenchyme and weakly throughout the nerve cord (black arrow). Weak staining can also be seen in the endodermal strand in initial and early tailbud stages (i, j, m, n). From early tailbud onwards, a strong domain of expression exists within the centre of the sensory vesicle (black single arrowhead) (j, k, l, n, o, p), which remains even when staining becomes weaker in the rest of the CNS in the mid-late tailbud (k, l, o, p). q i-v Schematic showing cell and tissue fates through developing embryos. Schematics are made from traces of the embryos in (e, f, m, o), though numbers of cells displayed may not be absolutely accurate due to cell membranes not being visible in different focal planes. q v Represents a transverse section through the plane shown by the dotted line in (q iv). Presumptive notochord cells are shown in red, endoderm yellow, muscle orange, epidermis gray, nerve cord dark blue and sensory vesicle light blue. a-d and i-l represent dorsal views, whilst e-h and m-p represent lateral views. Lower case lettering refers to the stage of development; g, gastrula; en, early neurula; n, neurula; ln, late neurula; itb, initial tailbud; etb, early tailbud; mtb, mid tailbud; ltb, late tailbud. Scale bars represent 100 μm