Figure 9.

Transcriptional control of stomodeal bra expression. A) Endodermal and stomodeal expression of bra during blastula stage. While endodermal bra can be seen at early blastula, stomodeal bra expression (marked by “*”) starts later and can be observed at 20h early mesenchyme blastula stage. B) Diagram of assay protocol testing for direct nodal targets by temporarily blocking Nodal signaling. Nodal signaling pathway inhibitor SB-431542 (SB) was added to cultures of sea urchin embryos at 24h, and gene expression was analyzed at 28h. C, QPCR assessment of effects of temporary SB treatment at indicated concentrations. This treatment significantly reduced the expression levels of nodal and not, but had small effects on bra levels. D, WMISH observations of effects of treatment with SB. Stomodeal bra expression is wiped out by 4h SB treatment, but endodermal bra expression is not affected; foxa stomodeal expression is diminished and endodermal expression is not affected. E) Effect of ets4 plus sip1 MASO on early bra expression. WMISH shows that ets4 and sip1 are required for proper timing expression of stomodeal bra expression; ets4/sip1 MASOs resulted in abnormal ectodermal bra expression during the early blastula stage. lv—lateral view; av— apical view. * marks stomodeal bra or foxa. All embryos in lateral or vegetal views were shown with the oral ectoderm facing left.