Figure 3.

Coherent Feedforward Regulation of Maternal Wnt/β-Catenin Target Genes in Late Blastula

(A) siamois1, siamois2 (also known as twin) and double Morpholino (MO) knockdown causes reduced expression of maternal Wnt/β-catenin target genes (at late blastula stage 9) (see also Figures S4A–S4F).

(B) Rescue of siamois1 and siamois2 knockdown with constitutively activating siamois construct (which is not targeted by either MO) re-instates expression of maternal Wnt/β-catenin target genes (nodal3, goosecoid, noggin).

(C) Stage-specific sampling of gene expression reveals that direct maternal Wnt/β-catenin target genes of the first class (siamois1 and nodal3) remain unaffected (st. 8), whereas expression of direct maternal Wnt/β-catenin target genes of the second class (goosecoid, noggin) is reduced (st.9). Also note that expression of zygotic Wnt8/β-catenin target genes (hoxd1, msx1) is not reduced but may be increased presumably owing to indirect mechanisms.

(D) Coherent feedforward regulation of some direct maternal Wnt/β-catenin target genes of the second class (e.g., goosecoid) involves siamois genes, which are among direct maternal Wnt/β-catenin target genes of the first class. Control Morpholino (control MO-injected embryos); Uninjected Control (uninjected embryos); sia1 MO, sia2 MO (embryos injected with Morpholino targeting siamois1 or siamois2 [also known as twin], respectively; VP16-sia RNA (Xenopus tropicalis embryos injected with Xenopus laevis constitutively active siamois mRNA [Kessler, 1997]). Data are from one representative of three independent experiments; error bars represent mean ± SEM of three technical replicates with p ≤ 0.05.