Figure 1. Activation of
ttx-3 Expression by POP-1 and Repression by SYS-1(A) Classic target genes are activated by TCF associated with b-catenin when the Wnt pathway is active and repressed by TCF when the Wnt pathway is inactive. Opposite target genes are activated by TCF when the Wnt pathway is inactive and repressed by the TCF:b-catenin complex when the Wnt pathway is active.(B) Expression of the POP-1::GFP (qIs74) and SYS-1::VENUS (qIs95) fusion proteins in the NBSMDD/AIY (Ant.) and NBSIAD/SIBV (Post.) neuroblasts identified with thehlh-16p::his::mCherry transgene (promoter of the
hlh-16 gene driving an histone fused to mCherry, stIs10546) at epidermal enclosure.(C) Effect of
pop-1 and
sys-1 loss-of-function mutants on the initiation of
ttx-3 expression (
ttx-3p::gfp, otIs173) at epidermal enclosure. As
pop-1(
q772)and
sys-1(
q736) homozygote mutants are lethal (at later embryonic stages), we scored the progeny of heterozygote mothers. Around one-fourth of theprogeny displays a phenotype as expected from Mendelian segregation (n = number of lineages analyzed). Note that in
sys-1 mutants the ectopic expressionin NBSIAD/SIBV is always weaker than the endogenous expression in NBSMDD/AIY (see picture). This may be due to the fact that
sys-1 loss of function is only partial(due to maternal contribution) and/or to the fact that NBSIAD/SIBV has a lower nuclear concentration of POP-1 than NBSMDD/AIY. See also Figure S1.(D) Expression of a POP-1 version lacking the SYS-1 interaction domain (
hlh-16p::DNpop-1) but not a full-length version (
hlh-16p::fullpop-1) ectopically activatesttx-3 expression (
ttx-3p::gfp, mgIs18) in the NBSIAD/SIBV neuroblast. The
hlh-16 promoter that drives expression in NBSMDD/AIY and NBSIAD/SIBV is used as a driver.Six independent lines were analyzed for
hlh-16p::DNpop-1 and eight for
hlh-16p::fullpop-1 (none: control without any
pop-1 transgene). The percentage ofembryos showing ectopic expression in each of the
hlh-16p::DNpop-1 lines is low but statistically significant (p < 0.01, Fisher's exact test; n = 50; error bars showSE of proportion). Note that the ectopic expression in NBSIAD/SIBV is always weaker than the endogenous expression in NBSMDD/AIY (see picture). Scale bar, 2 um.