Dominant expression of a distinctive V14⁺ T-cell antigen receptor α chain in mice

A distinctive variable region 14-positive (V14⁺) α chain (V(α)14⁺) of the T-cell antigen receptor is predominantly expressed in multiple mouse subspecies. The V(α)14 family has two members, V(α)14.1 and V(α)14.2, which differ by only three amino acids at positions 50-52. Based on the EcoRI restriction fragment length polymorphism of the gene encoding V(α)14, mice can be divided into three groups: type I with an 11.2-kilobase (kb) fragment, type II with a 2.0-kb fragment, and type III with the 2.0-kb and 11.2-kb fragments. Usage of V(α)14-J(α)281, where J(α)281 is an α-chain joining segment, with a one-base N region dominates at the level of 0.02-1.5% of α chains in all laboratory strains, Mus musculus castaneus, and Mus musculus domesticus but not in Mus musculus molossinus, Mus musculus musculus, and Mus spicilegus samples. The preferential V(α)14-J(α)281 expression seems to be due to positive selection because the V-J junctional region is always glycine, despite the ability of the V(α)14 gene to associate with J(α) other than J(α)281. As V(α)14-J(α)281 expression is independent of known major histocompatibility complex antigens, including H-2, TLA, Qa, and HMT, the selecting ligand must be a monomorphic molecule of the mouse, expressed in a subspecies-specific manner. Additional observations, such as the expression of homogeneous V(α)14-J(α)281 in athymic mice, suggest that the positive selection of V(α)14⁺ T cells occurs extrathymically.