We have therefore reevaluated the expression patterns of the genes used to direct PML-RARA expression in mice: PML-RARA directed from the CTSG, Ctsg and S100A8 (MRP8) loci cause APL; expression directed by regulatory elements from the cFes and Itgam (CD11b) loci do not [1], [2], [3], [19], [20]. Here, CTSG is linked to acute promyelocytic leukemia.