Function and factor interactions of a locus control region element in the mouse T cell receptor-alpha/Dad1 gene locus

Locus control regions (LCRs) refer to cis-acting elements composed of sever al DNase I hypersensitive sites, which synergize to protect transgenes from integration-site dependent effects in a tissue-specific manner. LCRs have been identified in many immunologically important gene loci, including one between the TCR delta /TCR alpha gene segments and the ubiquitously express ed Dad1 gene. Expression of a transgene under the control of all the LCR el ements is T cell specific. However, a subfragment of this LCR is functional in a wide variety of tissues. How a ubiquitously active element can partic ipate in tissue-restricted LCR activity is not clear. In this study, we loc alize the ubiquitously active sequences of the TCR-alpha LCR to an 800-bp r egion containing a prominent DNase hypersensitive site. In isolation, the a ctivity in this region suppresses position effect transgene silencing in ma ny tissues. A combination of in vivo footprint examination of this element in widely active transgene and EMSAs revealed tissue-unrestricted factor oc cupancy patterns and binding of several ubiquitously expressed transcriptio n factors. In contrast, tissue-specific, differential protein occupancies a t this element were observed in the endogenous locus or full-length LCR tra nsgene. We identified tissue-restricted AML-1 and Elf-1 as proteins that po tentially act via this element. These data demonstrate that a widely active LCR module can synergize with other LCR components to produce tissue-speci fic LCR activity through differential protein occupancy and function and pr ovide evidence to support a role for this LCR module in the regulation of b oth TCR and Dad1 genes.