Bilaterian anterior marker genes are expressed at the aboral pole of <i>Nematostella.</i>

<p>(A1–E7) In situ hybridizations, probes are indicated on the left; developmental stages above the images. (A–E2, A–E3, A–E5, and A–E6) are lateral views, from planula stage on with the aboral pole to the left. At the blastula stage, embryos are oriented with the assumption that the staining is continuous between the blastula and gastrula stage. Note that the future oral and aboral sides cannot be distinguished morphologically prior to gastrulation. (A–E4 and A–E7) are aboral views. Expression domains of <i>NvSix3/6</i>, <i>NvFoxQ2a</i>, <i>NvIrx</i>, and <i>NvFGFa1</i> are highly similar until the gastrula stage and then segregate into mutually exclusive domains. <i>NvFoxJ1</i> expression becomes detectable only after gastrulation. (F1 and F2) Double in situ hybridization with <i>NvSix3/6</i> (red) and <i>NvFGFa2</i> (blue) probes, showing the early restriction of the <i>NvFGFa2</i> expression from the gastrula stage on. (G–I) Schematic representation of the three types of aboral expression patterns: (G) “ring genes,” (H) “spot genes,” and (I) “late genes.” Synexpression groups are indicated on the right side; genes that have been described previously are shown in gray. Note that <i>NvSoxB(1)</i>, <i>NvHoxF/Anthox1</i>, and <i>NvFGF8a</i> have additional expression domains not indicated in the cartoon.