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. 2015 Oct 21;11(10):e1005585. doi: 10.1371/journal.pgen.1005585

Fig 7. Updated model for TCF-mediated lineage diversification.

Fig 7

A) Examples of wild-type expression patterns for genes that require TCF primarily for repression or activation. Repressed genes have exclusive (ceh-27) or equal (tbx-11) expression in SYS-1 Low-High lineages (yellow arrows), while activated genes have exclusive (nhr-67) or stronger (ceh-13) expression in SYS-1 High-High lineages (white arrows). B) Expression in SYS-1 High-High lineages for all genes and synthetic enhancers assayed. SYS-1 High-High score is the fraction of expressing lineages that are SYS-1 High-High. Expression is significantly more limited to SYS-1 High-High lineages for genes that require POP-1 for activation (green) than repression (purple) (p = 0.004, Wilcoxon rank sum test), as predicted by our model. C) A proposed model of TCF-mediated lineage patterning in C. elegans embryos. POP-1 and β-catenin concentrations vary depending on previous signaling history. Cells that are consecutive posterior daughters (pp) have the highest β-catenin levels and are predicted to strongly activate POP-1 targets. Consecutive anterior daughters (aa) have the highest POP-1 levels and are predicted to most strongly repress POP-1 targets. Single-anterior and single-posterior daughters (pa, ap) are predicted to have intermediate levels of repression and activation, respectively. D) Proposed model for the potential role of context transcription factors in determining the type of TCF regulation. When POP-1 is present, all targets are repressed by high levels of nuclear POP-1 and activated by SYS-1 and moderate levels of POP-1. We hypothesize that POP-1 RNAi reveals the activity of the context factors co-regulating a gene. We predict genes requiring TCF for activation are co-regulated by weak context factors that cannot activate transcription in the absence of POP-1, while genes requiring TCF for repression are co-regulated by context factors that can activate robust expression independently. Genes that are both activated and repressed (dual) could be co-regulated by context factors that produce moderate expression in the absence of POP-1.