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Mutations in the transcriptional regulator Mecp2 cause the severe X-linked neurodevelopmental disorder Rett syndrome (RTT). In this study, we investigate genes that function downstream of MeCP2 in cerebral cortex circuitry, and identify upregulation of Irak1, a central component of the NF-κB pathway. We show that overexpression of Irak1 mimics the reduced dendritic complexity of Mecp2-null cortical callosal projection neurons (CPN), and that NF-κB signalling is upregulated in the cortex with Mecp2 loss-of-function. Strikingly, we find that genetically reducing NF-κB signalling in Mecp2-null mice not only ameliorates CPN dendritic complexity but also substantially extends their normally shortened lifespan, indicating broader roles for NF-κB signalling in RTT pathogenesis. These results provide new insight into both the fundamental neurobiology of RTT, and potential therapeutic strategies via NF-κB pathway modulation., Rett syndrome is a neurodevelopmental disorder caused by mutations in Mecp2. Here the authors show that Mecp2 loss-of-function leads to upregulation of the NF-κB pathway, and that reducing NF-κB signalling ameliorates phenotypes of Mecp2-null mice, thus offering a potential therapeutic strategy.

While years of investigation have elucidated many aspects of embryonic stem cell (ESC) regulation, the contributions of post-transcriptional and translational mechanisms to the pluripotency network remain largely unexplored. In particular, little is known in ESCs about the function of RNA binding proteins (RBPs), the protein agents of post-transcriptional regulation. We performed an unbiased RNAi screen of RBPs in an ESC differentiation assay and identified two related genes, NF45 (Ilf2) and NF90/NF110 (Ilf3), whose knockdown promoted differentiation to an epiblast-like state. Characterization of NF45 KO, NF90 + NF110 KO, and NF110 KO ESCs showed that loss of NF45 or NF90 + NF110 impaired ESC proliferation and led to dysregulated differentiation down embryonic lineages. Additionally, we found that NF45 and NF90/NF110 physically interact and influence the expression of each other at different levels of regulation. Globally across the transcriptome, NF45 KO ESCs and NF90 + NF110 KO ESCs show similar expression changes. Moreover, NF90 + NF110 RNA immunoprecipitation (RIP)-seq in ESCs suggested that NF90/NF110 directly regulate proliferation, differentiation, and RNA-processing genes. Our data support a model in which NF45, NF90, and NF110 operate in feedback loops that enable them, through both overlapping and independent targets, to help balance the push and pull of pluripotency and differentiation cues.

Establishment, maintenance, and exit from pluripotency require precise coordination of a cell's molecular machinery. Substantial headway has been made in deciphering many aspects of this elaborate system, particularly with respect to epigenetics, transcription, and noncoding RNAs. Less attention has been paid to posttranscriptional regulatory processes such as alternative splicing, RNA processing and modification, nuclear export, regulation of transcript stability, and translation. Here, we introduce the RNA binding proteins that enable the posttranscriptional regulation of gene expression, summarizing current and ongoing research on their roles at different regulatory points and discussing how they help script the fate of pluripotent stem cells.

Ectopic expression of specific factors such as Oct4, Sox2, and Klf4 (OSK) is sufficient to reprogram somatic cells into induced pluripotent stem cells (iPSCs). In this study, we examine the paths taken by cells during the reprogramming process by following the transcriptional activation of two pluripotent miRNA clusters (mir-290 and mir-302) in individual cells in vivo and in vitro with knockin reporters. During embryonic development and embryonic stem cell differentiation, all cells sequentially expressed mir-290 and mir-302. In contrast, during OSK-induced reprogramming, cells activated the miRNA loci in a stochastic, nonordered manner. However, the addition of Sall4 to the OSK cocktail led to a consistent reverse sequence of locus activation (mir-302 then mir-290) and increased reprogramming efficiency. These results demonstrate that cells can follow multiple paths during the late stages of reprogramming, and that the trajectory of any individual cell is strongly influenced by the combination of factors introduced. © 2014 Elsevier Inc.