Rsp1 Is Indispensable for mRNA Stability during Erythroid Terminal Differentiation

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 [