| Popis: |
Aberrant expansion of hematopoietic stem and progenitor cells (HSPCs) is a major hallmark of myelodysplastic syndromes (MDS), although the underlying molecular regulation remains poorly understood. DEAD-box Helicase 41 (DDX41) is an understudied MDS-mutated factor whose function in hematopoiesis is unknown. Using an in vivo zebrafish model of Ddx41-deficiency, we unveiled a critical role for this helicase in regulating HSPCs. Mutants for ddx41 have more HSPCs than their siblings as measured by in situ hybridization and quantification by flow cytometry. We determined that in vivo Ddx41 suppresses the accumulation of R-loops, nucleic acid structures consisting of RNA:DNA hybrids and ssDNAs whose equilibrium is essential for cellular homeostasis. Using both global and hematovascular-restricted expression of RNASEH1-GFP to deplete R-loops, we revealed that excess R-loops in ddx41 mutants promote HSPC expansion. To uncover potential mechanisms driving HSPC expansion in ddx41 mutants, we identified elevated inflammatory target gene expression in HSPCs from ddx41 mutants compared to sibling controls using RNA-seq analysis. We established that excess R-loop levels induced by ddx41 deficiency triggered TBK1 phosphorylation and NFκB activation via the cGAS-STING pathway. Moreover, R-loop-triggered HSPC expansion was cGAS/STING-dependent. In human cells with diminished DDX41, blast counts, R-loop levels, and inflammatory signaling were elevated, suggesting a conservation of mechanism. These findings delineate a functional consequence for R-loop imbalance in HSPC biology and establish an in vivo link between R-loops, inflammation, and hematopoiesis. |
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