Abstract
MicroRNAs (miRs) are small noncoding RNAs that regulate gene expression posttranscriptionally by binding to the 3' untranslated regions of their target mRNAs. The evolutionarily conserved microRNA-125a (miR-125a) is highly expressed in both murine and human hematopoietic stem cells (HSCs), and previous studies have found that miR-125 strongly enhances self-renewal of HSCs and progenitors. In this study we explored whether temporary overexpression of miR-125a would be sufficient to permanently increase HSC self-renewal or, rather, whether persistent overexpression of miR-125a is required. We used three complementary in vivo approaches to reversibly enforce expression of miR-125a in murine HSCs. Additionally, we interrogated the underlying molecular mechanisms responsible for the functional changes that occur in HSCs on overexpression of miR-125a. Our data indicate that continuous expression of miR-125a is required to enhance HSC activity. Our molecular analysis confirms changes in pathways that explain the characteristics of miR-125a overexpressing HSCs. Moreover, it provides several novel putative miR-125a targets, but also highlights the complex molecular changes that collectively lead to enhanced HSC function.
Highlights
ABD is responsible for the experiments that led to Figure 2B and C
These »22-nucleotide-long noncoding RNAs are integrated into RNA-induced silencing complexes (RISCs) that mediate the interaction between miRs and their target mRNAs
In this study, we showed how continuous overexpression of miR-125a is required for the potent induction of hematopoietic stem cells (HSCs) potential that is initiated by this miR, both in vitro and in vivo
Summary
ABD is responsible for the experiments that led to Figure 2B and C. Because of the high evolutionary conservation, all mature miR-125 family members are present in organisms ranging from nematodes to mammals [6] and have the same seed sequence in both mouse and human. On ectopic overexpression of miR-125a, the self-renewal capacity of HSCs is increased in both murine and human cells [8]. Remains unclear whether the continuous activity of miR-125 is required or whether temporary overexpression of miR-125 in HSCs is sufficient to induce their long-term self-renewal. We used a reversible expression system (in three different setups) to assess to what extent temporary activation of miR-125a is sufficient to increase the potential of HSCs. We show that reversal of miR-125a overexpression reverts HSCs back to their normal state. Continuous expression of miR-125a is needed to induce self-renewing HSC activity. We identify molecular pathways that explain the phenotype that is induced on miR-125a overexpression and identify novel HSC-specific miR125a-associated gene expression changes
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