Rac1 deletion results in the inhibition of thymic ontogeny.

4-hydroxy-tamoxifen treatment of K14CreERxRac1^flox/flox MTS24⁺ E13.5 thymic epithelial cells (Rac1KO/4OHT+) blocks the generation of a thymic microenvironment after heterotopic transplantation under the kidney capsule (B) compared to untreated controls (Rac1KO/4OHT− shown) (A). (C–E) K5 and K14 staining confirming the presence of thymic medullary epithelial cells in control cells (shown are untreated MTS24⁺ K14CreERxRac1^flox/flox (Rac1KO/4OHT−))^which were capable of generating a functional thymic microenvironment as indicated by the presence of CD4⁺ (C) and CD8⁺ cells. (A and B ×20); Scale bars (C and D) 20 µm. FACS analysis of splenocytes derived from nude mice grafted with K14CreERxRac1^flox/flox MTS24⁺cells in absence of Tamoxifen showed peripheral CD4 and CD8 positive populations confirming the function of the thymic grafts (H) while with tamoxifen treated mice (I) showed no maturation of peripheral lymphocytes consistent with untansplanted nude mice (J). The dot plots show cells labelled with anti-CD4 and anti-CD8 antibodies gated on a CD3⁺ population.