Do RAR1 and RAR2 play unique roles during granulocyte differentiation?
Both RAR1 and RAR2 are expressed in cells of the neutrophil lineage (Labrecque et al., 1998; A Zelent, personal communication), although it is unclear what their specific roles are in these cells. One clue may lie in the conflicting data produced from our laboratory (Kastner et al., 2001) and those of Labrecque et al. (1998). We reported that myeloid progenitors from RAR-/- adult bone marrow or RAR-/-RAR-/- fetal liver are not blocked in their differentiation (and in fact differentiate with a faster kinetics than WT cells). In contrast, Labrecque et al. (1998) showed that granulocyte progenitors from RAR1-/-RAR-/- 18.5 d.p.c. fetal bone marrow are mostly blocked at the myelocyte/metamyelocyte stage of differentiation when cultured with SCF, IL3 and Epo; further differentiation was induced by the addition of RA. Since RAR2 is presumably still expressed in RAR1-/-RAR-/- myeloid cells, RAR1 and RAR2 might perform distinct functions in promyelocytes. The results from Labrecque et al. (1998
