Let‐7 and miR‐125 cooperate to prime progenitors for astrogliogenesis

Abstract

© 2015 The Authors. The molecular basis of astrocyte differentiation and maturation is poorly understood. As microRNAs have important roles in cell fate transitions, we set out to study their function during the glial progenitor cell (GPC) to astrocyte transition. Inducible deletion of all canonical microRNAs in GPCs in vitro led to a block in the differentiation to astrocytes. In an unbiased screen, the reintroduction of let-7 and miR-125 families of microRNAs rescued differentiation. Let-7 and miR-125 shared many targets and functioned in parallel to JAK-STAT signaling, a known regulator of astrogliogenesis. While individual knockdown of shared targets did not rescue the differentiation phenotype in microRNA-deficient GPCs, overexpression of these targets in wild-type GPCs blocked differentiation. This finding supports the idea that microRNAs simultaneously suppress multiple mRNAs that inhibit differentiation. MicroRNA-regulated transcripts exhibited concordant changes during in vivo differentiation and were enriched for a gene set upregulated in glioblastomas, consistent with validity of using the in vitro model to study in vivo events. These findings provide insight into the microRNAs and the genes they regulate in this important cell fate transition. Synopsis The coordinate action of multiple miRNAs is required to shape gene expression profiles in glial progenitor cells and allow differentiation to astrocytes, thereby underscoring the central role for miRNAs in cell fate transitions. Loss of Dgcr8 and subsequent loss of miRNAs leads to separable defects in astrocyte differentiation and survival. The differentiation defect is characterized in part by reduced JAK-STAT signaling, which can be rescued with exogenous LIF. Let-7 and miR-125 add-back can rescue parts of differentiation, independent of JAK-STAT signaling. Let-7 and miR-125 have many shared targets in glial progenitor cells, some of which act as barriers to differentiation. mRNAs regulated by let-7 and miR-125 are similarly modulated during astrocyte differentiation in vivo and are misexpressed in glioma stem cells. The coordinate action of multiple miRNAs is required to shape cellular gene expression profiles and facilitate transition from glial progenitor cells to astrocytes.