Functionally distinct roles for T and Tbx6 during mouse development

Abstract

The mouse T-box transcription factors T and Tbx6 are co-expressed in the primitive streak and have unique domains of expression; T is expressed in the notochord, while Tbx6 is expressed in the presomitic mesoderm. T-box factors are related through a shared DNA binding domain, the T-domain, and can therefore bind to similar DNA sequences at least in vitro. We investigated the functional similarities and differences of T and Tbx6 DNA binding and transcriptional activity in vitro and their interaction genetically in vivo. We show that at one target, Dll1, the T-domains of T and Tbx6 have different affinities for the binding sites present in the mesoderm enhancer. We further show using in vitro assays that T and Tbx6 differentially affect transcription with Tbx6 activating expression tenfold higher than T, that T and Tbx6 can compete at target gene enhancers, and that this competition requires a functional DNA binding domain. Next, we addressed whether T and Tbx6 can compete in vivo. First, we generated embryos that express Tbx6 at greater than wild-type levels embryos and show that these embryos have short tails, resembling the T heterozygous phenotype. Next, using the dominant-negative TWis allele, we show that Tbx6+/− TWis/+ embryos share similarities with embryos homozygous for the Tbx6 hypomorphic allele rib-vertebrae, specifically fusions of several ribs and malformation of some vertebrae. Finally, we tested whether Tbx6 can functionally replace T using a knockin approach, which resulted in severe T null-like phenotypes in chimeric embryos generated with ES cells heterozygous for a Tbx6 knockin at the T locus. Altogether, our results of differences in affinity for DNA binding sites and transcriptional activity for T and Tbx6 provide a potential mechanism for the failure of Tbx6 to functionally replace T and possible competition phenotypes in vivo.

Differential Occupancy and Regulatory Interactions of KDM6A in Bladder Cell Lines

“…Therefore, we plotted the correlation between HHEX , HES1 expression, and the expression of genes associated with the term ‘regulation of developmental process’ in the normal-immortal cluster ( Figure 1 D) for primary bladder cancer [ 45 , 46 , 47 , 48 ]. This analysis revealed a striking positive and corresponding negative correlation for the expression of developmental transcription factors such as GRHL2 , GRHL3 , ZBTB7B , and TBX6 [ 49 , 50 , 51 ], and the expression of HES1 and HHEX , respectively ( Figure 4 E). Conducting a similar analysis using CCLE bladder cancer cell line data showed comparable patterns for these factors, albeit with slightly more scattered clustering ( Figure S5C ).…”

Differential occupancy and regulatory interactions of KDM6A in bladder cell lines

“…Therefore, we plotted the correlation between HHEX, HES1 expression and the expression of the genes associated with the term ‘regulation of developmental process’ for Normal-Immortal cluster (Figure 1D) for primary bladder cancer [40–43]. This analysis revealed a striking positive and corresponding negative correlation for the expression of developmental transcription factors such as GRHL2, GRHL3, ZBTB7B, TBX6 [44–46], and the expression of HES1 and HHEX, respectively (Figure 4E). Making a similar analysis using CCLE bladder cancer cell line data showed comparable patterns for these factors albeit with a bit more scattered clustering (Figure S4C).…”

New insights into mesoderm and endoderm development, and the nature of the onychophoran blastopore

“…Another class of T-box genes that is involved in endoderm and mesoderm development is Tbx6 , a target of bra reviewed i [ 22 , 77 ], that diverged into Tbx6 , vegT and MGA in vertebrates (with vegT being lost in mammals) [ 53 ]. One key function of Tbx6 -class genes in vertebrates is the determination of the endomesoderm, another is organization, separation and development of endoderm and mesoderm [ 78 – 86 ], (reviewed in Wardle and Papaioannou [ 22 ]). Like bra , Tbx6-class genes are expressed in the primitive streak in vertebrates, but are not so in the forming mesodermal somites [ 71 , 87 , 88 ].…”