Fig. 2

Canonical Wnt signaling affects tailbud notochord progenitor fate through sox2 repression. (A-H) Heat shock-inducible transgenic lines were used to manipulate canonical Wnt signaling or sox2 expression after gastrulation at the 12-somite stage, and stained for ntla or flh expression 3 h after the heat shock. Loss of Wnt signaling causes a reduction in ntla expression specifically in the notochord progenitor domain (A,B, yellow dashed line indicates the progenitor domain), as well as a reduction in the notochord progenitor marker flh (E,F). Activation of Wnt signaling has the opposite effect on notochord progenitors (C,G). (I,J) sox2 is normally expressed in regions directly adjacent to the notochord progenitor domain (I) and expands dramatically into the notochord progenitor domain 2h after loss of Wnt signaling at the 12-somite stage (J, arrowhead). Heat shock induction of sox2 expression phenocopies Wnt loss of function with respect to ntla (D, dashed yellow line) and flh (H) expression. A sox2 reporter line shows weak fluorescence in notochord cells at the 16-somite stage (K,K′, arrowheads), indicating that notochord cells were once sox2 positive. The number of embryos showing the illustrated phenotype among the total number examined is indicated.