Trap1a is an X-linked and cell-intrinsic regulator of thymocyte development

The X-linked Trap1a gene encodes the tumor rejection antigen P1A,which is expressed in fetal tissues and multiple lineages of tumor cells.The function of this gene remains unknown.Using chimeric mice with wild-type(WT)and Trap1a^(−/y)bone marrow,we show that Trap1a^(−/y)donor cells are capable of generating most lineages of hematopoietic cells,with the notable exception of T cells.Deletion of Trap1a selectively arrests T-cell development at double-negative stage 1(DN1,with a CD4^(−)CD8^(−)CD25^(−)CD44^(+)phenotype).Because Trap1a is expressed in Lin^(−)Sca-1^(+)c-Kit^(+)and common lymphoid progenitors but not in immature thymocytes(DN1-DN4),Trap1a mutations affect the differentiation potential of progenitor cells without directly acting on T cells.Despite a similarity in the blockade of DN1 to DN2 transition,the Trap1a^(−/y)DN1 cells have normal expression of c-Kit,in contrast to what was reported in the Notch1^(−/−)DN1.Complementary DNA profiling of Trap1a^(−/y)and WT embryonic stem cells shows that Trap1a does not regulate the Notch pathway.Our data reveal that Trap1a is an X-linked regulator that affects the differentiation potential of progenitor cells into T cells through a Notch-independent mechanism and identify an important function for the Trap1a gene.