The gene encoding the ribosomal protein S19 (RPS19) is frequently mutated in Diamond-Blackfan anemia (DBA), a congenital erythroblastopenia. The consequence of these mutations on the onset of the disease remains obscure. Here, we show that RPS19 plays an essential role in biogenesis of the 40S small ribosomal subunit in human cells. Knockdown of RPS19 expression by siRNAs impairs 18S rRNA synthesis and formation of 40S subunits and induces apoptosis in HeLa cells. Pre-rRNA processing is altered, which leads to an arrest in the maturation of precursors to the 18S rRNA. Under these conditions, pre-40S particles are not exported to the cytoplasm and accumulate in the nucleoplasm of the cells in perinuclear dots. Consistently, we find that ribosome biogenesis and nucleolar organization is altered in skin fibroblasts from DBA patients bearing mutations in the RPS19 gene. In addition, maturation of the 18S rRNA is also perturbed in cells from a patient bearing no RPS19-related mutation. These results support the hypothesis that DBA is directly related to a defect in ribosome biogenesis and indicate that yet to be discovered DBArelated genes may be involved in the synthesis of the ribosomal subunits. IntroductionDiamond-Blackfan anemia (DBA) is a rare pure red blood cell aplasia of childhood characterized by the absence or decreased numbers of erythroid precursors in the bone marrow but an otherwise normal cellularity. Approximately 40% of the DBA patients present various somatic malformations that mostly occur in the cephalic area but also in the hand and/or limb, urogenital tract, and heart. [1][2][3] Clinical expression in DBA is highly heterogeneous, and evolution of the disease is unpredictable. Treatment includes steroid therapy and transfusion with iron chelation. Bone marrow or cord blood transplantation is the only curative treatment but requires an HLA-matched sibling and is mostly reserved to patients with severe complications.It has been established that 25% of the DBA patients bear a mutated allele of the gene encoding the ribosomal protein S19 (RPS19). [4][5][6] RPS19 is one of the 32 proteins that assemble with the 18S ribosomal RNA (rRNA) to form the small (40S) ribosomal subunit. RPS19 is an essential protein, as homozygous deletion of RPS19 in the mouse leads to embryonic lethality before implantation at the blastocyst stage. 7 A wide range of mutations have been identified in DBA patients, from missense to nonsense mutations and from partial to complete deletion of one allele. 3,5,6 Some missense mutations affect both the stability and the intracellular transport of RPS19. 8 Consistent with a role in DBA pathogenesis, depletion of RPS19 with specific siRNAs severely alters proliferation and differentiation of erythroleukemic cell lines or CD34 ϩ cells in culture. [9][10][11] Although DBA is to date the only genetic disease linked to mutation of an autosomal ribosomal protein gene, a number of other bone marrow failure symptoms (dyskeratosis congenita, cartilagehair hypoplasia, and Shwachman-Diamond ...

Congenital dyserythropoietic anemias (CDAs) constitute a rare group of inherited red-blood-cell disorders associated with dysplastic changes in late erythroid precursors. CDA type I (CDAI [MIM 224120], gene symbol CDAN1) is characterized by erythroid pathological features such as internuclear chromatin bridges, spongy heterochromatin, and invagination of the nuclear membrane, carrying cytoplasmic organelles into the nucleus. A cluster of 45 highly inbred Israeli Bedouin with CDAI enabled the mapping of the CDAN1 disease gene to a 2-Mb interval, now refined to 1.2 Mb, containing 15 candidate genes on human chromosome 15q15 (Tamary et al. 1998). After the characterization and exclusion of 13 of these genes, we identified the CDAN1 gene through 12 different mutations in 9 families with CDAI. This 28-exon gene, which is transcribed ubiquitously into 4738 nt mRNA, was reconstructed on the basis of gene prediction and homology searches. It encodes codanin-1, a putative o-glycosylated protein of 1,226 amino acids, with no obvious transmembrane domains. Codanin-1 has a 150-residue amino-terminal domain with sequence similarity to collagens and two shorter segments that show weak similarities to the microtubule-associated proteins, MAP1B (neuraxin) and synapsin. These findings, and the cellular phenotype, suggest that codanin-1 may be involved in nuclear envelope integrity, conceivably related to microtubule attachments. The specific mechanisms by which codanin-1 underlies normal erythropoiesis remain to be elucidated.