Expression of ectoderm markers in normal, lithium-treated, and zinc-treated embryos. Shown are whole-mount in situ hybridizations (WISHs) of ectodermal marker genes on blastula stage (columns 1, 3, and 5) and gastrula stage (columns 2, 4, and 6) sea urchin embryos. The genes under considerations are indicated on the right hand side. Expression of apical plate marker genes (hpf4, FoxQ2, and secreted frizzled protein 1/5 [sFRP1/5]) is lost in lithium-treated embryos (columns 3 and 4) and expanded in zinc-treated embryos (columns 5 and 6). Expression of the oral ectoderm marker chordin is shifted to the 'new' animal pole region in lithium-treated embryos (columns 3 and 4) but lost in blastula stage zinc-treated embryos (column 5). However, ectodermal differentiation does appear to take place in zinc-treated embryos if they are left to recover for a longer period of time (column 6). The ciliated band marker gene onecut exhibits wild-type-like expression in lithium-treated embryos, with a ring of expression around the animal pole (columns 3 and 4). The apical expression domain of onecut co-expands like the other apical organ markers in zinc-treated embryos (panels 5 and 6). Strikingly, the expression of aboral ectoderm markers (IrxA, Nkx2.2, and tbx2) is lost in blastula stage lithium-treated embryos (panel 3), whereas it is enhanced in zinc-treated blastula stage embryos, in which the expression appears to be quite uniformly distributed. Tbx2 is expressed in mesodermal cells and in the aboral ectoderm in normal embryos (columns 1 and 2). Strikingly, the ectodermal expression only is lost in lithium-treated embryos, whereas the mesodermal domain remains (compare with Figure 4).