Erythropoiesis in the Rps19 disrupted mouse: Analysis of erythropoietin response and biochemical markers for Diamond-Blackfan anemia

Department of Genetics and Pathology, The Rudbeck Laboratory, Uppsala University, 751 85 Uppsala, Sweden; Molecular Medicine and Gene Therapy, The Strategic Center for Stem Cell Biology and Cell Therapy, Lund University, Lund, Sweden; Unit of Clinical Chemistry, Karolinska Hospital, Huddinge, Sweden; Department of Medical Sciences, Clinical Chemistry, Uppsala Akademiska Hospital, Uppsala, Sweden
Blood Cells Molecules and Diseases (Impact Factor: 2.33).

ABSTRACT The human ribosomal protein S19 gene (RPS19) is mutated in approximately 20% of patients with Diamond-Blackfan anemia (DBA), a congenital disease with a specific defect in erythropoiesis. The clinical expression of DBA is highly variable, and subclinical phenotypes may be revealed by elevated erythrocyte deaminase (eADA) activity only. In mice, complete loss of Rps19 results in early embryonic lethality whereas Rps19+/− mice are viable and without major abnormalities including the hematopoietic system. We have performed a detailed analysis of the Rps19+/− mice. We estimated the Rps19 levels in hematopoietic tissues and we analyzed erythrocyte deaminase activity and globin isoforms which are used as markers for DBA. The effect of a disrupted Rps19 allele on a different genetic background was investigated as well as the response to erythropoietin (EPO). From our results, we argue that the loss of one Rps19 allele in mice is fully compensated for at the transcriptional level with preservation of erythropoiesis.

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    ABSTRACT: Diamond-Blackfan anaemia (DBA) is a congenital anaemia and broad developmental disease that develops soon after birth. The anaemia is due to failure of erythropoiesis, with normal platelet and myeloid lineages, and it can be managed with steroids, blood transfusions, or stem cell transplantation. Normal erythropoiesis after transplantation shows that the defect is intrinsic to an erythroid precursor. DBA is inherited in about 10-20% of cases, and genetic studies have identified mutations in a ribosomal protein gene, RPS19, in 25% of cases; there is evidence for involvement of at least two other genes. In yeast, RPS19 deletion leads to a block in ribosomal RNA biogenesis. The critical question is how mutations in RPS19 lead to the failure of proliferation and differentiation of erythroid progenitors. While this question has not yet been answered, understanding the biology of DBA may provide insight not only into the defect in erythropoisis, but also into the other developmental abnormalities that are present in about 40% of patients, and into the cancer predisposition that is inherent to DBA.
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    ABSTRACT: The ribosome is an evolutionarily conserved organelle essential for cellular function. Ribosome construction requires assembly of approximately 80 different ribosomal proteins (RPs) and four different species of rRNA. As RPs co-assemble into one multi-subunit complex, mutation of the genes that encode RPs might be expected to give rise to phenocopies, in which the same phenotype is associated with loss-of-function of each individual gene. However, a more complex picture is emerging in which, in addition to a group of shared phenotypes, diverse RP gene-specific phenotypes are observed. Here we report the first two mouse mutations (Rps7(Mtu) and Rps7(Zma)) of ribosomal protein S7 (Rps7), a gene that has been implicated in Diamond-Blackfan anemia. Rps7 disruption results in decreased body size, abnormal skeletal morphology, mid-ventral white spotting, and eye malformations. These phenotypes are reported in other murine RP mutants and, as demonstrated for some other RP mutations, are ameliorated by Trp53 deficiency. Interestingly, Rps7 mutants have additional overt malformations of the developing central nervous system and deficits in working memory, phenotypes that are not reported in murine or human RP gene mutants. Conversely, Rps7 mouse mutants show no anemia or hyperpigmentation, phenotypes associated with mutation of human RPS7 and other murine RPs, respectively. We provide two novel RP mouse models and expand the repertoire of potential phenotypes that should be examined in RP mutants to further explore the concept of RP gene-specific phenotypes.
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    ABSTRACT: Over the past decade, genetic lesions that cause ribosome dysfunction have been identified in both congenital and acquired human disorders. These discoveries have established a new category of disorders, known as ribosomopathies, in which the primary pathophysiology is related to impaired ribosome function. The protoptypical disorders are Diamond-Blackfan anemia, a congenital bone marrow failure syndrome, and the 5q- syndrome, a subtype of myelodysplastic syndrome. In both of these disorders, impaired ribosome function causes a severe macrocytic anemia. In this review, we will discuss the evidence that defects in ribosomal biogenesis cause the hematologic phenotype of Diamond-Blackfan anemia and the 5q- syndrome. We will also explore the potential mechanisms by which a ribosomal defect, which would be expected to have widespread consequences, may lead to specific defects in erythropoiesis.
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