Abstract
BackgroundTBX1 (T-box transcription factor 1) is a major candidate gene that likely contributes to the etiology of velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS). Although the haploinsufficiency of TBX1 in both mice and humans results in congenital cardiac malformations, little has been elucidated about its upstream regulation. We aimed to explore the transcriptional regulation and dysregulation of TBX1.MethodsDifferent TBX1 promoter reporters were constructed. Luciferase assays and electrophoretic mobility shift assays (EMSAs) were used to identify a cis-regulatory element within the TBX1 promoter region and its trans-acting factor. The expression of proteins was identified by immunohistochemistry and immunofluorescence. Variants in the cis-regulatory element were screened in conotruncal defect (CTD) patients. In vitro functional assays were performed to show the effects of the variants found in CTD patients on the transactivation of TBX1.ResultsWe identified a cis-regulatory element within intron 1 of TBX1 that was found to be responsive to GATA6 (GATA binding protein 6), a transcription factor crucial for cardiogenesis. The expression patterns of GATA6 and TBX1 overlapped in the pharyngeal arches of human embryos. Transfection experiments and EMSA indicated that GATA6 could activate the transcription of TBX1 by directly binding with its GATA cis-regulatory element in vitro. Furthermore, sequencing analyses of 195 sporadic CTD patients without the 22q11.2 deletion or duplication identified 3 variants (NC_000022.11:g.19756832C > G, NC_000022.11:g.19756845C > T, and NC_000022.11:g. 19756902G > T) in the non-coding cis-regulatory element of TBX1. Luciferase assays showed that all 3 variants led to reduced transcription of TBX1 when incubated with GATA6.ConclusionsOur findings showed that TBX1 might be a direct transcriptional target of GATA6, and variants in the non-coding cis-regulatory element of TBX1 disrupted GATA6-mediated transactivation.
Highlights
TBX1 (T-box transcription factor 1) is a major candidate gene that likely contributes to the etiology of velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS)
Previous studies have shown that TBX1 is regulated by sonic hedgehog (Shh) signaling [32, 33], vascular endothelial growth factor (VEGF) [34] and Ripply3 [35] or has a feedback loop with retinoic acid (RA) signaling [36], which are involved in pharyngeal arch development
We demonstrated that the expression patterns of TBX1 and GATA binding protein 6 (GATA6) overlapped in the pharyngeal arches of human embryos
Summary
TBX1 (T-box transcription factor 1) is a major candidate gene that likely contributes to the etiology of velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS). Previous studies have shown that TBX1 is regulated by sonic hedgehog (Shh) signaling [32, 33], vascular endothelial growth factor (VEGF) [34] and Ripply3 [35] or has a feedback loop with retinoic acid (RA) signaling [36], which are involved in pharyngeal arch development. How these signals affect the transcriptional regulation of TBX1 remains unclear. The study of the cis-regulatory elements of TBX1 will help to further understand the role of TBX1 in the occurrence of CTD
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