No abstract

Lamins are structural components of the nuclear lamina (NL) that regulate genome organization and gene expression, but the mechanism remains unclear. Using Hi-C, we show that lamins maintain proper interactions among the topologically associated chromatin domains (TADs) but not their overall architecture. Combining Hi-C with fluorescence in situ hybridization (FISH) and analyses of lamina-associated domains (LADs), we reveal that lamin loss causes expansion or detachment of specific LADs in mouse ESCs. The detached LADs disrupt 3D interactions of both LADs and interior chromatin. 4C and epigenome analyses further demonstrate that lamins maintain the active and repressive chromatin domains among different TADs. By combining these studies with transcriptome analyses, we found a significant correlation between transcription changes and the interaction changes of active and inactive chromatin domains These findings provide a foundation to further study how the nuclear periphery impacts genome organization and transcription in development and NL-associated diseases.

The fragile X mental retardation protein FMRP regulates translation of its bound mRNAs through incompletely defined mechanisms. FMRP has been linked to the microRNA pathway and we show here that it associates with the RNA helicase MOV10, also associated with the microRNA pathway. FMRP associates with MOV10 directly and in an RNA-dependent manner and facilitates MOV10-association with RNAs in brain and cells suggesting a cooperative interaction. We identified the RNAs recognized by MOV10 using RNA-IP and iCLIP. Examination of the fate of MOV10 on RNAs revealed a dual function for MOV10 in regulating translation: it facilitates microRNA-mediated translation of some RNAs but also increases expression of other RNAs by preventing AGO2 function. The latter subset was also bound by FMRP in close proximity to the MOV10 binding site, suggesting that FMRP prevents MOV10-mediated microRNA suppression. We have identified a new mechanism for FMRP-mediated translational regulation through its association with MOV10.

BackgroundAlzheimer’s disease (AD) is an inexorable neurodegenerative disease that commonly occurs in the elderly. The cognitive impairment caused by AD is associated with abnormal accumulation of amyloid-β (Aβ) and hyperphosphorylated tau, which are accompanied by inflammation. Neural stem cells (NSCs) are self-renewing, multipotential cells that differentiate into distinct neural cells. When transplanted into a diseased brain, NSCs repair and replace injured tissues after migration toward and engraftment within lesions. We investigated the therapeutic effects in an AD mouse model of human NSCs (hNSCs) that derived from an aborted human fetal telencephalon at 13 weeks of gestation. Cells were transplanted into the cerebral lateral ventricles of neuron-specific enolase promoter-controlled APPsw-expressing (NSE/APPsw) transgenic mice at 13 months of age.ResultsImplanted cells extensively migrated and engrafted, and some differentiated into neuronal and glial cells, although most hNSCs remained immature. The hNSC transplantation improved spatial memory in these mice, which also showed decreased tau phosphorylation and Aβ42 levels and attenuated microgliosis and astrogliosis. The hNSC transplantation reduced tau phosphorylation via Trk-dependent Akt/GSK3β signaling, down-regulated Aβ production through an Akt/GSK3β signaling-mediated decrease in BACE1, and decreased expression of inflammatory mediators through deactivation of microglia that was mediated by cell-to-cell contact, secretion of anti-inflammatory factors generated from hNSCs, or both. The hNSC transplantation also facilitated synaptic plasticity and anti-apoptotic function via trophic supplies. Furthermore, the safety and feasibility of hNSC transplantation are supported.ConclusionsThese findings demonstrate the hNSC transplantation modulates diverse AD pathologies and rescue impaired memory via multiple mechanisms in an AD model. Thus, our data provide tangible preclinical evidence that human NSC transplantation could be a safe and versatile approach for treating AD patients.Electronic supplementary materialThe online version of this article (doi:10.1186/s13024-015-0035-6) contains supplementary material, which is available to authorized users.

The fragile X mental retardation protein FMRP is an RNA binding protein that associates with a large collection of mRNAs. Since FMRP was previously shown to be a nucleocytoplasmic shuttling protein, we examined the hypothesis that FMRP binds its cargo mRNAs in the nucleus. The enhanced green fluorescent protein-tagged FMRP construct (EGFP-FMRP) expressed in Cos-7 cells was efficiently exported from the nucleus in the absence of its nuclear export sequence and in the presence of a strong nuclear localization sequence (the simian virus 40 [SV40] NLS), suggesting an efficient mechanism for nuclear export. We hypothesized that nuclear FMRP exits the nucleus through its bound mRNAs. Using silencing RNAs to the bulk mRNA exporter Tap/NXF1, we observed a significantly increased number of cells containing EGFP-FMRP in the nucleus, which was further augmented by removal of FMRP's nuclear export sequence. Nuclear-retained SV40-FMRP could be released upon treatment with RNase. Further, Tap/NXF1 coimmunoprecipitated with EGFP-FMRP in an RNA-dependent manner and contained the FMR1 mRNA. To determine whether FMRP binds pre-mRNAs cotranscriptionally, we expressed hemagglutinin-SV40 FMRP in amphibian oocytes and found it, as well as endogenous Xenopus FMRP, on the active transcription units of lampbrush chromosomes. Collectively, our data provide the first lines of evidence that FMRP binds mRNA in the nucleus.Fragile X syndrome is one of the most common forms of inherited mental retardation, affecting approximately 1/4,000 males and 1/8,000 females (reviewed in reference 34). Fragile X syndrome is caused by the loss of expression of the fragile X mental retardation protein FMRP (32,40,64,77,84), which is a highly conserved RNA binding protein with two KH domains and an RGG box (6,70,71). The N terminus (2, 86), KH1 domain (1), KH2 domain (17), and the RGG box (12,18,69) have all been reported to bind RNA. FMRP is estimated to associate with approximately 4% of brain mRNAs (6, 12), and two large collections of associated mRNAs have been described (12, 58). FMRP is primarily cytoplasmic by both immunostaining and biochemical fractionation (22, 30); however, it contains a functional, nonclassical nuclear localization sequence (NLS) near its N terminus (7,24,73). Immunogold studies have shown that FMRP is present in the neuronal nucleoplasm and within nuclear pores (30). In addition, the presence of FMRP in the nucleus is regulated temporally, such that at specific times during development, FMRP is predominantly nuclear. Studies in Xenopus tropicalis embryos showed that FMRP was largely nuclear 2 h postfertilization (stage 6), suggesting a special nuclear function during this developmental period (9). Zebrafish embryos also demonstrated predominantly nuclear FMRP staining very early in development, 3 h postfertilization (81). Interestingly, these time points coincide with times in development when no zygotic transcription is taking place (62), providing indirect evidence that FMRP export from the nucleus might depend on mRNA synthe...