Rabbit Anti-Human TCF3 monoclonal antibody, clone TZ1369

Tcf7l1 (also known as Tcf3) is a bimodal transcription factor that plays essential roles in embryogenesis and embryonic and adult stem cells. On one hand, Tcf7l1 works as transcriptional repressor via the recruitment of Groucho-related transcriptional corepressors to repress the transcription of Wnt target genes, and, on the other hand, it activates Wnt target genes when Wnt-activated beta-catenin interacts with it. However, how its activity is modulated is not well understood. Here we demonstrate that a JmjC-domain containing protein, Jmjd6, interacts with Tcf7l and derepresses Tcf7l. We show that Jmjd6 binds to a region of Tcf7l1 that is also responsible for Groucho interaction, therefore making it possible that Jmjd6 binding displaces the Groucho transcriptional corepressor from Tcf7l1. Moreover, we show that Jmjd6 antagonizes the repression effect of Tcf7l1 on target gene transcription and is able to enhance beta-catenin-induced gene activation and that, vice versa, inhibition of Jmjd6 activity compromises gene activation in both cells and Xenopus early embryos. We also show that jmjd6 is both maternally and zygotically transcribed during Xenopus embryogenesis. Loss of Jmjd6 function causes defects in anterioposterior body axis formation and down-regulation of genes that are involved in anterioposterior axis patterning. The results elucidate a novel mechanism underlying the regulation of Tcf7l1 activity and the regulation of embryonic body axis formation.

Embryogenesis relies on the precise interplay of signaling cascades to activate tissue-specific differentiation programs. An important player in these morphogenetic processes is beta-catenin, which is a central component of adherens junctions and canonical Wnt signaling. Lack of beta-catenin is lethal before gastrulation, but mice heterozygous for beta-catenin (Ctnnb1) develop as wild type. Here, we confine beta-catenin amounts below the heterozygous expression level to study the functional consequences for development. We generate embryonic stem (ES) cells and embryos expressing beta-catenin only from the ubiquitously active ROSA26 promoter and thereby limit beta-catenin expression to similar to 12.5% (ROSA26(beta/+)) or similar to 25% (ROSA26(beta/beta)) of wild-type levels. ROSA26(beta/+) is sufficient to maintain ES cell morphology and pluripotent characteristics, but is insufficient to activate canonical target genes upon Wnt stimulation. This Wnt signaling deficiency is incompletely restored in ROSA26(beta/beta) ES cells. We conclude that even very low.-catenin levels are able to sustain cell adhesion, but not Wnt signaling. During development, ROSA26(beta/beta) as well as ROSA26(beta/+) partially rescues the knockout phenotype, yet proper gastrulation is absent. These embryos differentiate according to the neural default hypothesis, indicating that gastrulation depends on high beta-catenin levels. Strikingly, if ROSA26(beta/+) or ROSA26(beta/beta) is first activated after gastrulation, subsequent development correlates with the dosage of beta-catenin. Moreover, molecular evidence indicates that the amount of beta-catenin controls the induction of specific Wnt target genes. In conclusion, by restricting its expression we determine the level of beta-catenin required for adhesion or pluripotency and during different morphogenetic events.