GATA mRNA expression during development in A. queenslandica . Late blastulae (A; sensu Leys and Degnan ), mid-stage embryos with a pigment spot (ps) (B), late-stage embryos with a pigment ring (pr) (C), a free-swimming larva (D), a settlement stage postlarva (E), and a juvenile (F-I) were labelled with the antisense riboprobe AqGATA. The juvenile in I is labelled with DAPI and an anti-tyrTub antibody. In B-D, the specimens are viewed from the lateral side with the posterior pigmented structures (ps and pr) placed up in each panel. In E and F, the specimens are viewed from the top of postlarva. Medial optical sections exposing the internally localised subepithelial cells are shown. Insets in B and C show GATA expression in individual subepithelial cells (arrowheads), and an inset in D shows the demarcation between the GATA-negative epidermal layer (ep) and the strongly GATA-positive subepithelial domain (su). An inset in E shows the downregulation of GATA expression in the subepithelial domain (su) relative to the outer layer epithelium at settlement. Arrowheads in F indicate the internal spicule-forming tent-pole-like structures in the juvenile that strongly express GATA. In G, an inset shows a GATA-expressing choanocyte with a cilium (ci) and a basal nucleus (nu). An arrowhead in H shows a cluster of GATA-expressing spicule (sp)-forming cells at the apex of the tent-pole-like structures shown in F; note in I that their cell bodies (arrowhead) are situated basal to the pinacoderm (pi). Scale bars: 100 μm (A-F), 50 μm (H, I, and insets in B-E), 10 μm (G). DAPI, 4',6-diamidino-2-phenylindole.