Fig. 3

Developmental expression of Sp-fat1, Sp-fat4, Sp-pcdh9, and Sp-dchs2 analyzed by whole mount in situ hybridization. All four genes show strikingly similar patterns of expression. Prior to the mesenchyme blastula stage, faint signal is seen in all cells and is highest in the basal cytoplasm (arrowhead, A’’’). By the late mesenchyme blastula (MB) stage, signal is enriched in the apical plate (arrowhead, B) and vegetal plate (arrowhead, B’’) but is absent from migrating primary mesenchyme cells (arrowhead, B’). At the early gastrula (EG) and mid-gastrula (MG) stages, intense signal is seen at the margin of the blastopore (arrowhead, C’’) and in the apical plate, but ingressing non-skeletogenic mesenchyme cells at the tip of the archenteron are unlabeled (arrowhead, D’). At the early prism (EP) stage, expression is detected primarily in the apical plate, the prospective foregut, and at the margin of the blastopore (arrowheads, E). At the pluteus (PL) stage, expression is elevated in the apical plate (arrowhead, G’), the portion of the ciliary band overlying the postoral arms (arrowhead, G), and in the gut (arrowhead, F’). FP- focal plane. PHB- pre-hatching blastula (16 hpf). MB- mesenchyme blastula (24 hpf). EG- early gastrula (28 hpf). MG- mid-gastrula (30–32 hpf). EP- early prism (44 hpf). PL- pluteus (72 hpf). Each pluteus was imaged in two different focal planes (FP1 and FP2). Scale bar = 50 μm