Studies have suggested that binding of the SATB1 protein to L2a, a matrix 
association region located 4.5 kb 5' to the mouse CD8alpha gene, positively 
affects CD8 expression in T cells. Therefore, experiments were performed to 
determine the effect on T cell development of reduced expression of SATB1. 
Because homozygous SATB1-null mice do not survive to adulthood due to non-thymus 
autonomous defects, mice were produced that were homozygous for a T 
cell-specific SATB1-antisense transgene and heterozygous for a SATB1-null 
allele. Thymic SATB1 protein was reduced significantly in these mice, and the 
major cellular phenotype observed was a significant reduction in the percentage 
of CD8SP T cells in thymus, spleen, and lymph nodes. Mice were smaller than wild 
type but generally healthy, and besides a general reduction in cellularity and a 
slight increase in surface CD3 expression on CD8SP thymocytes, the composition 
of the thymus was similar to wild type. The reduction in thymic SATB1 does not 
lead to the variegated expression of CD8-negative single positive thymocytes 
seen upon deletion of several regulatory elements and suggested by others to 
reflect failure to activate the CD8 locus. Thus, the present results point to an 
essential role for SATB1 late in the development and maturation of CD8SP T 
cells.