alas 2 encodes the erythroid-specific S-aminolevulinate synthase (ALAS2), the first enzyme in the heme biosynthetic pathway, which is expressed exclusively in erythroid cells. In our previous study in vivo, we demonstrated that alas2-null primitive erythroid cells resulted in an maturation arrest as well as in massive cytoplasmic iron accumulation, suggesting that ALAS2 is necessary for differentiation of primitive erythroid cells. However, the role of ALAS2 on definitive erythropoiesis remained unclear, because a/as2-null mutants died in utero by 11.5 embryonic days due to severe anemia. To study the effect of heme deficiency in differentiating definitive erythroid cells, ES cells lacking alas2 were induced to undergo erythroid differentiation by co-culturing with OP9 cells. Phenotypes of floating cells on day 8 and day 14, corresponding to primitive and definitive erythroid cells, respectively, were examined. Both alas2-nul\ primitive and definitive erythroid cells were totally white due to a marked deficiency of heme, despite the fact that erythroblasts showed identical morphology to that of the wild type. Among erythroid-specific genes, expression of TER119, an erythroid-specific antigen, as well as transferrin receptor, were markedly decreased in a/as2-null primitive erythroid cells, while they were not affected in alas2-null definitive erythroid cells. Of note, the non-specific ALAS gene (alas1) was upregulated both in primitive and definitive a/os2-null erythroid cells. These findings indicate that heme deficiency principally affects erythroid differentiation of primitive erythroid cells, but not that of definitive erythroid cells. In addition, alasl expression in both primitive and definitive erythroid cells is under heme-mediated feedback control as in the liver, and alas1 derepression by heme deficiency in alas2-m\\ primitive erythroid ceils may represent a partial compensatory mechanism for heme deficiency, however, it is far too insufficient.
|Issue number||11 PART I|
|Publication status||Published - 2000 Dec 1|
ASJC Scopus subject areas
- Cell Biology