Erythroid-specific 5-aminolevulinate synthase (ALAS-E) catalyzes the first step of heme biosynthesis in higher organisms, and molecular defects of human ALAS-E gene are reported to result in the X-linked sideroblastic anemia (XLSA). Appearance of ring sideroblasts, which possess mitochondria! iron deposits surrounding nucleus, is a clinical hallmark of XLSA. We recently showed that targeting disruption of murine alas-e causes embryonic lethality by 11.5-dpc due to severe anemia and intensive iron accumulation in cytosol of blood cells. The mode of iron accumulation in the ALAS-E-null primitive erythroid cells is distinct from that of the ring sideroblasts. Ring sideroblasts have been observed only in the definitive erythroid cells. To investigate the roles ALAS-E plays during definitive hematopoiesis, which begins from 9.5-10.5-dpc, we performed a partial rescue experiment of alas-e -deficient mice from the embryonic lethality, using ALAS-E transgenic mouse lines that express human ALAS-E under the regulatory influence of GATA-1 gene locus. The GATA-1 gene locus was engineered to drive the transgene expression only in the primitive erythroid tissues. We crossbred female mice heterozygous for the ALAS-E-null mutant allele with mîle ALAS-E transgenic mice to obtain human alas-e-positive embryos hemizygous for t le alas-e mutant allele (ALAS-E (-/Y)::hALAS-E). The ALAS-E (-/Y)::hALAS-E embryos survived after 11.5-dpc, indicating that tfie human ALAS-E transgene sustained the embryo lives slightly longer. The partially rescu ;d embryos at 12.5-dpc showed pale appearance and no positive signals of benzidine staini ig which detects hemoglobin. Surprisingly, they contained numerous ring sideroblasts in blood cells. This is in contrast to the ALAS-E mutant embryos, in that we had never observed any ring sideroblasts in the embryos. An immunohistostaining experiment reveal :d that ey globin protein, which are expressed exclusively in primitive erythroid cells, is expressed in the ring sideroblasts, indicating that the ring sideroblasts are derived from t le primitive erythroid lineage. These results suggest that the ring sideroblast formation is related to the differentiation stage of erythroid cells, rather than to ontogeny of hematopoiesis. Fetal livers of the ALAS-E (-/Y)::hALAS-E embryos containing ring sideroblasts exhibited rudimentary morphology, from which no erythropoiesis was expect ;d to occurred. This suggests that ALAS-E is also essential for the normal definitive.
|Issue number||11 PART I|
|Publication status||Published - 2000 Dec 1|
ASJC Scopus subject areas
- Cell Biology