SEPARATE ELEMENTS CONTROL DJ AND VDJ REARRANGEMENT IN A TRANSGENIC RECOMBINATION SUBSTRATE

We describe transgenic mice that carry an antigen receptor gene minilocus comprised of germline T cell receptor (TCR) β variable gene elements (V, D and J) linked to an immunoglobulin (Ig) Cμ constant region gene with or without a DNA segment containing the Ig heavy chain transcriptional enhancer (Eμ). Transgenic constructs lacking the Eμ-containing segment did not undergo detectable rearrangement in any tissue of six independent transgenic lines. In contrast, transgenic constructs containing this DNA segment underwent rearrangement at high frequency in lymphoid tissues, but not other tissues, of four independent lines. Analyses of purified B and T cells, as well as B and T cell lines, from transgenic animals demonstrated that the Eμ-containing segment within the construct allowed partial TCR gene assembly (D to J) in both B and T cells. However, complete TCR gene rearrangement within the construct (V to DJ) occurred only in T cells. Therefore, we have demonstrated elements that can control two separate aspects to TCRβ VDJ rearrangement within this construct. One lies within the Eμ-containing DNA segment and represents a dominant, cis-acting element that initiates lymphoid cell-specific Dβ to Jβ rearrangement; various considerations suggest this activity may be related to that of the Eμ element. The second element provides T cell-specific control of complete (Vβ to DJβ) variable region gene assembly; it correlates in activity with expression of the unrearranged Vβ segment.