HY-STOP Tcra locus is functional and can undergo antigen-independent secondary rearrangements. (A) Female HY-STOP thymocytes were stained for surface TCRβ, HYα, and Vα2 or Vα3.2. Note the presence of TCRβ⁺HYα⁻ cells (left), a fraction of which can be stained with Vα antibodies (center), and the lack of binding of Vα antibodies to TCRβ⁺HYα⁺ cells (right). Representative results of two independent experiments are shown. (B) Female HY-STOP thymocytes were stained for surface TCRβ, HYα, TCRβ8.1/8.2, CD4, and CD8α. Staining for TCRβ and TCRβ8.1/8.2 on HYα⁻ cells (left) and expression of CD4 and CD8α by TCRβ⁺HYα⁻ cells (right) is shown. Representative staining for one of three analyzed animals is shown.