Mouse models have proven invaluable for understanding erythropoiesis. Here, we describe an autosomal recessive inherited anemia in the mouse mutant hem6. Hematologic and transplantation analyses revealed a mild, congenital, hypochromic, microcytic anemia intrinsic to the hematopoietic system that is associated with a decreased red blood cell zinc protoporphyrin to heme ratio, indicative of porphyrin insufficiency. Iron uptake experiments showed that hem6 reticulocytes are defective in heme production, but not cellular iron uptake defects. Male hem6 mice are infertile due to defects in sperm structure and motility. Through positional cloning and BAC complementation, we identified the gene responsible for the hem6 anemia to be Rsp1 (RNAStabilityProtein1) on Chr.3. The anemia phenotype was reproduced by injecting zebrafish embryos with morpholinos specifically targeting the Rsp1 transcript. Multi-tissue, real-time PCR shows that Rsp1 is abundantly expressed in bone marrow and testis, which correlates with the anemia and infertility defects in the hem6 mutant. To further study the function of Rsp1, we conducted yeast two hybrid analysis, employing a human bone marrow library. We found that Rsp1 interacts with the poly (A)-binding protein cytoplasmic 1(PABPC1) and, using microarray analysis, showed that many abundant erythroid specific transcripts, including Hbb-b1, Hba-a1, Alas2, and Mitoferrin1, were significantly down regulated in hem6 reticulocytes. Since PABPC1 is responsible for stabilizing the Hba-a1 transcript [

Wang et al. (
1999
)
Mol Cell Biol
19
:
4552
–60
and
Wang and Kiledjian (
2000
)
Mol Cell Biol
20
:
6334
–41
], we hypothesized that the relative deficiency in erythroid-specific mRNAs in hem6 reticulocytes might be due to decreased mRNA stability. Indeed, serial microarray analysis of reticulocytes aged in vitro showed that numerous, abundantly expressed erythroid-specific transcripts decayed at faster rates in hem6 reticulocytes compared to control reticulocytes. Furthermore, these mRNAs also have progressively shorter poly (A) tails, suggesting a mechanism for the increased rate of decay. In sum, the evidence supports the conclusion that Rsp1 is a regulator of mRNA stability and gene expression during the terminal differentiation of erythroid cells.

Topics:
rna, messenger, anemia, heme, infertility, iron, bronchioloalveolar carcinoma, microcytic hypochromic anemia, polymerase chain reaction, porphyrins, positional cloning

Disclosures: No relevant conflicts of interest to declare.

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2008, The American Society of Hematology
2008
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