Let-7 represses Nr6a1 and a mid-gestation developmental program in adult fibroblasts [RNA-seq_siRNA_transfection]

MicroRNAs (miRNAs) are critical to proliferation, differentiation, and development. Here, we characterize gene expression in murine Dicer-null adult mesenchymal stem cell lines, a fibroblast cell type. Loss of Dicer leads to de-repression of let-7 targets at levels that exceed 10-100 fold with increases in transcription. Direct and indirect targets of this miRNA belong to a mid-gestation embryonic program that encompasses known oncofetal genes as well as oncogenes not previously associated with an embryonic state. Surprisingly, this mid-gestation program represents a distinct period that occurs between the pluripotent state of the inner cell mass at embryonic day 3.5 and the induction of let-7, upon differentiation, at embryonic day 10.5. Within this mid-gestation program, we characterize the let-7 target Nr6a1, an embryonic transcriptional repressor that regulates gene expression in adult fibroblasts following miRNA loss. In total, let-7 is required for the continual suppression of embryonic gene expression in adult cells, a mechanism that may underlie its tumor suppressive function. Overall design: mRNAs from adult mesenchymal stem cells (immortalized monoclonal lines of murine MSCs) with and without Dicer (WT: Dicer f/f, KO: Dicer -/-), were analyzed. WT and KO cells were transfected with a nontargeting control siRNA. KO cells were separately transfected with a synthetic let-7g siRNA duplex, or an siRNA targeting Nr6a1.

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Gurtan AM, Ravi A, Rahl PB, Bosson AD, JnBaptiste CK, Bhutkar A, Whittaker CA, Young RA, Sharp PA