Genetic screen identifies microRNA cluster 99b/let-7e/125a as a regulator of primitive hematopoietic cells

Abstract

Hematopoietic stem/progenitor cell (HSPC) traits differ between genetically distinct mouse strains. For example, DBA/2 mice have a higher HSPC frequency compared with C57BL/6 mice. We performed a genetic screen for microRNAs that are differentially expressed between LSK, LS ؊ K ؉ , erythroid and myeloid cells isolated from C57BL/6 and DBA/2 mice. This analysis identified 131 micro-RNAs that were differentially expressed between cell types and 15 that were differentially expressed between mouse strains. Of special interest was an evolutionary conserved miR cluster located on chromosome 17 consisting of miR-99b, let-7e, and miR-125a. All cluster members were most highly expressed in LSKs and down-regulated upon differentiation. In addition, these microRNAs were higher expressed in DBA/2 cells compared with C57BL/6 cells, and thus correlated with HSPC frequency. To functionally characterize these microRNAs, we overexpressed the entire miR-cluster 99b/ let-7e/125a and miR-125a alone in BM cells from C57BL/6 mice. Overexpression of the miR-cluster or miR-125a dramatically increased day-35 CAFC activity and caused severe hematopoietic phenotypes upon transplantation. We showed that a single member of the miR-cluster, namely miR-125a, is responsible for the majority of the observed miR-cluster overexpression effects. Finally, we performed genome-wide gene expression arrays and identified candidate target genes through which miR-125a may modulate HSPC fate. (Blood. 2012;119(2):377-387)

miR-99a/100∼125b tricistrons regulate hematopoietic stem and progenitor cell homeostasis by shifting the balance between TGFβ and Wnt signaling

“…Thus, despite targeting several common targets in the TGFb and Wnt pathway, miR99/100 and let-7 exert different effects on HSPCs than miR-125b. These observations are consistent with previous reports on the miR-99b;125a tricistron in the murine system (Guo et al 2010;Gerrits et al 2012). It was previously reported that miR-125a or miR-125b overexpression confers a competitive advantage to HSCs, leading to a gradual increase of chimerism in murine transplantation models (Guo et al 2010;Ooi et al 2010;Enomoto et al 2011).…”

“…It was previously reported that miR-125a or miR-125b overexpression confers a competitive advantage to HSCs, leading to a gradual increase of chimerism in murine transplantation models (Guo et al 2010;Ooi et al 2010;Enomoto et al 2011). When g-retroviral vectors were used, which increased miR-125 expression level by 500-fold to several thousand-fold, development of myeloproliferative disease (MPD) and leukemia was observed (Gerrits et al 2012;for discussion, see O'Connell et al 2010). Using a lentiviral system with a SFFV promoter-driven miRNA cassette, we achieved expression levels comparable with those seen in AMKL.…”

MiR-125 in normal and malignant hematopoiesis

“…Indeed, miR-125a is enriched in HSCs (up to 23-fold over total BM), particularly in long-term HSCs (up to 6-fold) 24,63,64 and downregulated upon differentiation. 64 MiR-125a was demonstrated to have a role in HSCs, increasing their number in vivo and in vitro, 63,64 and causing a myeloproliferative phenotype upon transplantation.…”

“…64 MiR-125a was demonstrated to have a role in HSCs, increasing their number in vivo and in vitro, 63,64 and causing a myeloproliferative phenotype upon transplantation. 64 Whereas Guo et al 63 showed amplification of the HSC pool upon sustained miR-125a overexpression, Gerrits et al 64 reported a decline of the primitive BM compartment and loss of competitive advantage upon secondary transplantation.…”

Complex oncogene dependence in microRNA-125a–induced myeloproliferative neoplasms

“…Although leukemia is induced by overexpression of miR-125b in several models (21,24,(26)(27)(28), myeloproliferation could be the predominant effect of miR-125a overexpression (20,29,30). To address oncogene addiction in the context of MPN, we first assessed the effects of constitutive miR-125a overexpression in vivo to gauge the phenotypes of an inducible miR-125a model to be described later.…”