EXPRESSION OF RHOMBOTIN 2 IN NORMAL AND LEUKEMIC HEMATOPOIETIC-CELLS

The rhombotin 2 gene was identified by its association with a recurren t chromosome translocation (11;14)(p13:q11), occurring in T-cell acute lymphoblastic leukaemias (ALLs). High levels of RBTN2 have been found in T-cell leukaemias carrying the translocation and in some T-cell AL Ls that lack, by cytogenetic and molecular techniques, translocations involving 11p13. In murine tissues RBTN2 has been found to be expresse d, with high levels present in brain and early B cells. Studies carrie d out in mice lacking RBTNZ have demonstrated the importance of this g ene in erythropoiesis. We have investigated the expression of RBTN2 in human leukaemic cells, and in human and murine normal myeloid progeni tor cells, RBTN2 is expressed in the leukaemic cells of patients with pre-B ALL, T-ALL and acute myeloblastic leukaemia (AML). By cytogeneti c and molecular techniques no abnormalities were noted in 11p13, Using clonogenic assays and single cell PCR we found that RBTN2 is expresse d strongly in the precursors of mixed erythrocyte/macrophage/mast, ery throcyte, megakaryocyte, neutrophil and macrophage colonies. In contra st, RBTN2 message was low to undetectable in the mature progeny. These findings indicate that RBTN2 is expressed in leukaemias of both the m yeloid and lymphoid lineages, Further, these studies show that in norm al myeloid and lymphoid cells the expression of RBTN2 is present in pr ogenitor cells and is lost as the cells terminally differentiate. This latter finding further illustrates that the detection of a RNA in a p opulation of cells should not be interpreted to mean that all of the c ells in that population express the RNA.