A conserved sequence block in the murine and human TCR Jα region: Assessment of regulatory function in vivo

Temporal control of rearrangement at the TCR α/δ locus is crucial for development of the γδ and αβ T cell lineages. Because the TCR δ locus is embedded within the α locus, rearrangement of any Vα-Jα excises the δ locus, precluding expression of a functional γδ TCR. Approximately 100 kb spanning the Cδ-Cα region has been sequenced from both human and mouse, and comparison has revealed an unexpectedly high degree of conservation between the two. Of interest in terms of regulation, several highly conserved sequence blocks (> 90% over > 50 bp) were identified that did not correspond to known regulatory elements such as the TCR α and δ enhancers or to coding regions. One of these blocks lying between Jα4 and Jα3, which appears to be conserved in other vertebrates, has been shown to augment TCR α enhancer function in vitro and differentially bind factors from nuclear extracts. To further assess a plausible regulatory role for this element, we have created mice in which this conserved sequence block is either deleted or replaced with a neomycin resistance gene driven by the phosphoglycerate kinase promoter (pgk-neo(r)). Deletion of this conserved sequence block in vivo did have a local effect on Jα usage, echoing the in vitro data. However, its replacement with pgk-neo(r) had a much more dramatic, long range effect, perhaps underscoring the importance of maintaining overall structure at this locus.