Transcriptional regulation by TBX2

Abstract

Tbx2 is a member of an evolutionarily conserved transcriptional regulatory gene family. Little is. known about th~ molecular mechanisms underlying the function of Tbx2. Because connexin43 ( Cx43) and Tbx2 are both expressed in neural crest derivatives in pharyngeal arches and because the promoter of Cx43 contains· direct repeats ofT (Brachyury) half sites, it is hypothesized that Tbx2 regulates Cx43 and other genes important for neural crest cell functions. TBX2 DNA binding affinity was analyzed by eletrophoretic mobility shift assays. Transcriptional regulation of the Cx43 promoter by Tbx2 was analyzed using reporter constructs. These results suggest that Cx43 is a bona fide target gene of Tbx2 and that Tbx2 negatively regulates Cx43 gene expression by binding to TCACAC sites. Moreover, dye-coupling assays showed that Tbx2 upregulation led to decreased junctional coupling. To identify other genes that may be regulated by Tbx2, a differential gene expression profile was determined using GEMl microarrays. CellSpace knowledgebase was used to perform functional assignments to Tbx2-regulated genes. This analysis indicated that Tbx2 might be involved in different fundamental cell functions. Tbx2 upregulates proliferation genes, downregulates tenascinC, and upregulates nidogen. In conclusion, together with Cx43 repression, Tbx2 may signal neural crest cells to stop migration and start p~oliferation. Gene cluster analysis also suggested a potential role for Tbx2 in osteogenesis. In accord, Tbx2 expression was detected in chondrocytes and osteocytes both in long bone and membranous bones.