Kinetic Analysis of npBAF to nBAF Switching Reveals Exchange of SS18 with CREST and Integration with Neural Developmental Pathways
Departments of Developmental Biology and Pathology, and Department of Genetics, Stanford University Medical School, Stanford, California 94305, and Department of Developmental Biology, Washington University School of Medicine, St. Louis, Missouri 63110.The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 06/2013; 33(25):10348-61. DOI: 10.1523/JNEUROSCI.1258-13.2013
During the development of the vertebrate nervous system, neural progenitors divide, generate progeny that exit mitosis, and then migrate to sites where they elaborate specific morphologies and synaptic connections. Mitotic exit in neurons is accompanied by an essential switch in ATP-dependent chromatin regulatory complexes from the neural progenitor Brg/Brm-associated factor (npBAF) to neuron-specific nBAF complexes that is in part driven by miR-9/9* and miR-124. Recapitulating this microRNA/chromatin switch in fibroblasts leads to their direct conversion to neurons. We have defined the kinetics of neuron-specific BAF complex assembly in the formation of induced neurons from mouse embryonic stem cells, human fibroblasts, and normal mouse neural differentiation and, using proteomic analysis, found that this switch also includes the removal of SS18 and its replacement by CREST at mitotic exit. We found that switching of chromatin remodeling mechanisms is highly correlated with a broad switch in the use of neurogenic transcription factors. Knock-down of SS18 in neural stem cells causes cell-cycle exit and failure to self-renew, whereas continued expression of SS18 in neurons blocks dendritic outgrowth, underlining the importance of subunit switching. Because dominant mutations in BAF subunits underlie widely different human neurologic diseases arising in different neuronal types, our studies suggest that the characteristics of these diseases must be interpreted in the context of the different BAF assemblies in neurons rather than a singular mammalian SWItch/sucrose nonfermentable (mSWI/SNF) complex.
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- "Although direct neuronal conversion may offer unique benefits, this approach is currently limited to a small number of protocols to specify neuronal subtypes using postnatal or adult human samples (Caiazzo et al., 2011; Liu et al., 2013; Ring et al., 2012; Son et al., 2011; Yoo et al., 2011). MiR-9/9* and miR-124 are critical components of a genetic pathway that controls the assembly of neuron-specific, ATPdependent chromatin remodeling complexes during neural development (Staahl et al., 2013; Yoo et al., 2009). In addition, these miRNAs have been shown to play key roles in the differentiation of neural progenitors to mature neurons by regulating the expression of antineural genes (Makeyev et al., 2007; Packer et al., 2008; Visvanathan et al., 2007; Xue et al., 2013). "
ABSTRACT: The ability to generate human neurons of specific subtypes of clinical importance offers experimental platforms that may be instrumental for disease modeling. We recently published a study demonstrating the use of neuronal microRNAs (miRNAs) and transcription factors to directly convert human fibroblasts to a highly enriched population of striatal medium spiny neurons (MSNs), a neuronal subpopulation that has a crucial role in motor control and harbors selective susceptibility to cell death in Huntington's disease. Here we describe a stepwise protocol for the generation of MSNs by direct neuronal conversion of human fibroblasts in 30 d. We provide descriptions of cellular behaviors during reprogramming and crucial steps involved in gene delivery, cell adhesion and culturing conditions that promote cell survival. Our protocol offers a unique approach to combine microRNAs and transcription factors to guide the neuronal conversion of human fibroblasts toward a specific neuronal subtype.
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ABSTRACT: A new water-soluble pillararene containing ten imidazolium groups was prepared. It can be used as a stabilizer to fabricate gold nanoparticles smaller than 6 nm in water.
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ABSTRACT: Several features make the chromatin environment of neurons likely to be different than any other cell type. These include the fact that several hundred types of neurons exist, each requiring specialized patterns of gene expression and in turn specialized chromatin landscapes. In addition, neurons have the most stable morphology of any cell type, a unique feature essential for memory. Yet these stable morphologies must allow the emergence of new stable morphologies in response to environmental influences permitting learning to occur by altered morphology and new synapse formation. Several years ago we found that neurons have specific chromatin remodeling mechanisms not present in any other cell type that are produced by combinatorial assembly of ATP-dependent chromatin remodeling complexes. The neural specific subunits are essential for normal neural development, learning and memory. Remarkably, recreating these neural specific complexes in fibroblasts leads to their conversion to neurons. Recently, the subunits of these complexes have been found to have genetically dominant roles in several human neurologic diseases. The genetic dominance of these mutations suggests that less severe mutations will contribute to phenotypic variation in human neuronally derived traits.
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