Mechanisms that direct ordered assembly of T cell receptor β locus V, D, and J gene segments.

TL;DR: It is demonstrated that V beta segments are preferentially targeted for rearrangement to Dbeta as opposed to Jbeta segments and that Vbeta segments can be appended to nonrearranged endogenous Dbeta segments in which the ability of D beta segments to join to J beta segments is eliminated.

Abstract: T cell receptor (TCR) β variable region genes are assembled in progenitor T cells from germ-line Vβ, Dβ, and Jβ segments via an ordered two-step process in which Dβ to Jβ rearrangements occur on both alleles before appendage of a Vβ to a preexisting DJβ complex. Direct joining of Vβ segments to nonrearranged Dβ or Jβ segments, while compatible with known restrictions on the V(D)J recombination mechanism, are infrequent within the endogenous TCRβ locus. We have analyzed mechanisms that mediate ordered Vβ, Dβ, and Jβ assembly via an approach in which TCRβ minilocus recombination substrates were introduced into embryonic stem cells and then analyzed for rearrangement in normal thymocytes by recombinase-activating gene 2-deficient blastocyst complementation. These analyses demonstrated that Vβ segments are preferentially targeted for rearrangement to Dβ as opposed to Jβ segments. In addition, we further demonstrated that Vβ segments can be appended to nonrearranged endogenous Dβ segments in which we have eliminated the ability of Dβ segments to join to Jβ segments. Our findings are discussed in the context of the mechanisms that regulate the ordered assembly and utilization of V, D, and J segments.