RESUMO
DDX41 mutations are the most common germline alterations in adult myelodysplastic syndromes (MDSs). The majority of affected individuals harbor germline monoallelic frameshift DDX41 mutations and subsequently acquire somatic mutations in their other DDX41 allele, typically missense R525H. Hematopoietic progenitor cells (HPCs) with biallelic frameshift and R525H mutations undergo cell cycle arrest and apoptosis, causing bone marrow failure in mice. Mechanistically, DDX41 is essential for small nucleolar RNA (snoRNA) processing, ribosome assembly, and protein synthesis. Although monoallelic DDX41 mutations do not affect hematopoiesis in young mice, a subset of aged mice develops features of MDS. Biallelic mutations in DDX41 are observed at a low frequency in non-dominant hematopoietic stem cell clones in bone marrow (BM) from individuals with MDS. Mice chimeric for monoallelic DDX41 mutant BM cells and a minor population of biallelic mutant BM cells develop hematopoietic defects at a younger age, suggesting that biallelic DDX41 mutant cells are disease modifying in the context of monoallelic DDX41 mutant BM.
Assuntos
RNA Helicases DEAD-box , Síndromes Mielodisplásicas , Animais , RNA Helicases DEAD-box/genética , Células Germinativas , Hematopoese/genética , Camundongos , Mutação/genética , Síndromes Mielodisplásicas/genéticaRESUMO
Vertebrates have evolved three paralogs, termed LUC7L, LUC7L2, and LUC7L3, of the essential yeast U1 small nuclear RNA (snRNA)-associated splicing factor Luc7p. We investigated the mechanistic and regulatory functions of these putative splicing factors, of which one (LUC7L2) is mutated or deleted in myeloid neoplasms. Protein interaction data show that all three proteins bind similar core but distinct regulatory splicing factors, probably mediated through their divergent arginine-serine-rich domains, which are not present in Luc7p. Knockdown of each factor reveals mostly unique sets of significantly dysregulated alternative splicing events dependent on their binding locations, which are largely non-overlapping. Notably, knockdown of LUC7L2 alone significantly upregulates the expression of multiple spliceosomal factors and downregulates glycolysis genes, possibly contributing to disease pathogenesis. RNA binding studies reveal that LUC7L2 and LUC7L3 crosslink to weak 5' splice sites and to the 5' end of U1 snRNA, establishing an evolutionarily conserved role in 5' splice site selection.
Assuntos
Leucemia Mieloide/genética , Síndromes Mielodisplásicas/genética , Proteínas Nucleares/genética , Splicing de RNA , Proteínas de Ligação a RNA/genética , Sequência de Bases , Éxons , Perfilação da Expressão Gênica , Regulação Neoplásica da Expressão Gênica , Humanos , Íntrons , Leucemia Mieloide/metabolismo , Leucemia Mieloide/patologia , Mutação , Síndromes Mielodisplásicas/metabolismo , Síndromes Mielodisplásicas/patologia , Proteínas Nucleares/metabolismo , RNA Nuclear Pequeno/genética , RNA Nuclear Pequeno/metabolismo , Proteínas de Ligação a RNA/metabolismo , Ribonucleoproteína Nuclear Pequena U1/genética , Ribonucleoproteína Nuclear Pequena U1/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Transdução de Sinais , SpliceossomosRESUMO
Hematopoietic stem and progenitor cells (HSPCs) arise during embryonic development and are essential for sustaining the blood and immune systems throughout life. Tight regulation of HSPC numbers is critical for hematopoietic homeostasis. Here, we identified DEAD-box helicase 41 (Ddx41) as a gatekeeper of HSPC production. Using zebrafish ddx41 mutants, we unveiled a critical role for this helicase in regulating HSPC production at the endothelial-to-hematopoietic transition. We determined that Ddx41 suppresses the accumulation of R-loops, nucleic acid structures consisting of RNA:DNA hybrids and ssDNAs whose equilibrium is essential for cellular fitness. Excess R-loop levels in ddx41 mutants triggered the cGAS-STING inflammatory pathway leading to increased numbers of hemogenic endothelium and HSPCs. Elevated R-loop accumulation and inflammatory signaling were observed in human cells with decreased DDX41, suggesting possible conservation of mechanism. These findings delineate that precise regulation of R-loop levels during development is critical for limiting cGAS-STING activity and HSPC numbers.
Assuntos
Embrião não Mamífero/citologia , Células-Tronco Hematopoéticas/citologia , Estruturas R-Loop , Proteínas de Peixe-Zebra/metabolismo , Animais , Animais Geneticamente Modificados , Diferenciação Celular , RNA Helicases DEAD-box/genética , RNA Helicases DEAD-box/metabolismo , Embrião não Mamífero/metabolismo , Células-Tronco Hematopoéticas/metabolismo , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Nucleotidiltransferases/genética , Nucleotidiltransferases/metabolismo , Transdução de Sinais , Peixe-Zebra , Proteínas de Peixe-Zebra/genéticaRESUMO
Somatic, heterozygous missense and nonsense mutations in at least seven proteins that function in the spliceosome are found at high frequency in MDS patients. These proteins act at various steps in the process of splicing by the spliceosome and lead to characteristic alterations in the alternative splicing of a subset of genes. Several studies have investigated the effects of these mutations and have attempted to identify a commonly affected gene or pathway. Here, we summarize what is known about the normal function of these proteins and how the mutations alter the splicing landscape of the genome. We also summarize the commonly mis-spliced gene targets and discuss the state of mechanistic unification that has been achieved. Finally, we discuss alternative mechanisms by which these mutations may lead to disease.
