Early expression of a T-cell receptor β-chain transgene suppresses rearrangement of the V(γ4) gene segment

β transgenic mice have a T-cell receptor β-chain gene that is prematurely expressed on the surface of CD4^-CD8^- thymocytes and paired with an uncharacterized non-T-cell receptor α-chain polypeptide. The rearrangement of the T-cell receptor variable region γ chain gene segment V(γ4), a component of the γ-chain gene that is rearranged and expressed preferentially on thymocytes of normal adult mice, is severely repressed in β transgenic mice. Consequently no γδ T-cell receptor heterodimers are detectable on the surface of adult thymocytes or splenic T cells. These results indicate that cells expressing αβ or γ(V(γ4))-δ TCRs originate from a common precursor in which the first productive rearrangement of either the β or γ locus determines the further differentiation pathway into either αβ or γδ T cells. The repression of V(γ4) rearrangement by a preexisting β-chain gene may be indicative of one of several mechanisms which ensure that γδ and αβ receptors do not as a rule appear on the surface of the same cell.