Sox-4 facilitates thymocyte differentiation.

The mouse Sry-like transcription factor Sox-4 is expressed in thymus, bone marrow, and gonads of adult mice. Sox-4-deficient mice die at embryonic day E14 due to cardiac malformation. In transfer experiments to irradiated recipients, B cell development was shown to be severely impaired in Sox-4-deficient progenitor cells. However, no drastic effects on T lymphocyte development were noted, despite the high level expression of the Sox-4 gene in the thymus of normal mice. Here, we report a detailed analysis of T cell development from Sox-4-deficient progenitors. Explanted fetal thymic organ cultures (FTOC) of Sox-4-deficient thymi yielded 10-50-fold fewer CD4 CD8 double-positive and single-positive cells than FTOC of littermates. This effect was T cell-autonomous, since similar observations were made when FTOC were performed by culturing of Sox-4-deficient progenitors in wild-type thymus lobes. When Sox-4-deficient fetal liver cells were injected together with normal cells intrathymically, they did not compete efficiently for reconstitution. It is concluded that Sox-4 facilitates thymocyte development.