PML RAR-ALPHA FUSION GENE IS EXPRESSED IN BOTH GRANULOID MACROPHAGE AND ERYTHROID COLONIES IN ACUTE PROMYELOCYTIC LEUKEMIA

Acute promyelocytic leukaemia (APL) associated with a t(15;17) translo cation generates a PML/RARalpha chimaeric gene which is transcribed as a fusion PML/RARalpha mRNA. To clarify the pathophysiologic role of P ML/RARalpha in APL patients, we examined the expression of PML/RARalph a in haemopoietic colonies in five patients with APL by reverse transc riptase polymerase chain reaction (RT-PCR) analysis. By the two-step R T-PCR method, we demonstrated that PML/RARalpha positive clones were p resent in progenitor cells including both CFU-GM and BFU-E in two case s. This result suggests that the translocation of PML/RARalpha occurre d in a pluripotent stem cell in some APL patients. In four patients we detected two amplified cDNA fragments of 780 and 640 bp which presuma bly arose by alternative splicing of the PML gene. Interestingly, of C FU-GM and BFU-E colonies examined in four patients, there were three d ifferent types of colonies: those expressing only the 780 bp fragment, those expressing only the 640 bp fragment, and those expressing both fragments. This suggests that alternative splicing was clonally determ ined in each colony. We describe a useful RT-PCR technique for the stu dy of gene expression in a limited number of haemopoietic precursor ce lls.