Project description:The Rbfox family of splicing factors regulate alternative splicing during animal development and in disease, impacting thousands of exons in the maturing brain, heart, and muscle. Rbfox proteins have long been known to bind to the RNA sequence GCAUG with high affinity, but just half of Rbfox CLIP peaks contain a GCAUG motif. We incubated recombinant RBFOX2 with over 60,000 mouse and human transcriptomic sequences to reveal significant binding to several moderate-affinity, non-GCAYG sites at a physiologically relevant range of RBFOX concentrations. We find that many of these “secondary motifs” bind Rbfox robustly in cells and that several together can exert regulation comparable to a GCAUG in a trichromatic splicing reporter assay. Furthermore, secondary motifs regulate RNA splicing in neuronal development and in neuronal subtypes where cellular Rbfox concentrations are highest, enabling a second wave of splicing changes as Rbfox levels increase.
Project description:To determine how the higher order assembly of Rbfox proteins affect Rbfox-dependent splicing regulation, we expressed Rbfox wildtype and its mutant protein in Flp-In™ T-REx™ 293 Rbfox2-/- cells and extracted RNA from these cells to perform RASL-seq which profiles thousands of alternative splicing event.
Project description:The axon initial segment (AIS) is a specialized neuronal compartment required for action potential generation and neuronal polarity. However, understanding the mechanisms regulating AIS structure and function has been hindered by an incomplete knowledge of its molecular composition. Here, using immuno-proximity biotinylation we further define the AIS proteome and its dynamic changes during neuronal maturation. Among the many AIS proteins identified, we show that SCRIB is highly enriched in the AIS both in vitro and in vivo, and exhibits a periodic architecture like the axonal spectrin-based cytoskeleton. We found that ankyrinG interacts with and recruits SCRIB to the AIS. However, loss of SCRIB has no effect on ankyrinG. This powerful and flexible approach further defines the AIS proteome and provides a rich resource to elucidate the mechanisms regulating AIS structure and function.
Project description:Early neuronal development is a well-coordinated process in which neuronal stem cells differentiate into polarized neurons. This process has been well studied in classical non-human model systems, but to what extent this is recapitulated in human neurons remains unclear. To study neuronal polarization in human neurons, we cultured human iPSC-derived neurons, characterized early developmental stages, measured electrophysiological responses, and systematically profiled transcriptomic and proteomic dynamics during these steps. We found extensive remodeling of the neuron transcriptome and proteome, with altered mRNA expression of ~1,100 genes and different expression profiles of ~1,500 proteins during neuronal differentiation and polarization. We also identified a distinct stage in axon development marked by an increase in microtubule remodeling and apparent relocation of the axon initial segment from the distal to proximal axon. Our comprehensive characterization and quantitative map of transcriptome and proteome dynamics provides a solid framework for studying polarization in human neurons.
Project description:Rett syndrome (RTT) is a severe neurological disorder which is mainly caused by mutations found in the X-linked gene encoding MeCP2. Despite extensive studies, the molecular functions of MeCP2 remain elusive. Here, we report that MeCP2 is a new subunit of a higher-order multiunit protein complex Rbfox/LASR and acts as a scaffold for this splicing complex. Deletion or mutation of MeCP2 leads to defects in forming MeCP2/Rbfox/LASR complex and aberrant alternative pre-mRNA splicing. Our data link RTT to an impaired function of MeCP2 in splicing control through its role in nucleating Rbfox/LASR macromolecule assembly.
Project description:The splicing regulator PTBP2 controls a program of embryonic splicing required for neuronal maturation. The splicing regulatory proteins PTBP1 and PTBP2 show distinct temporal expression profiles in the developing brain. Neuronal progenitor cells predominantly express PTBP1, whereas developing neurons express high levels of PTBP2, which are subsequently reduced late in neuronal maturation. We show here that PTBP2 and the program of splicing it controls are essential to proper neuronal maturation and survival. To investigate its in vivo function, we generated conditional PTBP2 null alleles in mice. Loss of PTBP2 in neuronal progenitor cells leads to neonatal death without gross defects in brain architecture. Mice with specific depletion of PTBP2 in the cortex and forebrain are viable. However over the first three postnatal weeks, when the normal cortex expands and develops mature circuits, the PTBP2 null cortices degenerate. We find that PTBP2-/- neurons cultured from embryonic brain show the same initial viability as wild type cells with proper early marker expression and neurite outgrowth. Strikingly, between 10 and 20 days in culture PTBP2 null neurons undergo a catastrophic failure to mature and die. To assess the target transcripts leading to these phenotypes, we examined the genomewide splicing changes in the PTBP2 null brains. This identified a large number of mis-regulated exons that share a temporal pattern of regulation; in the absence of PTBP2 many isoforms normally found in adults are precociously expressed in the developing brain. Transcripts following this pattern encode essential neuronal proteins affecting neurite growth, pre- and post-synaptic assembly, and synaptic transmission. Our results define a new genetic regulatory program essential for neuronal survival and maturation, where PTBP2 acts to temporarily repress expression of protein isoforms until the final maturation of the neuron. Mice carrying a conditional floxed PTBP2 allele of PTBP2 were crossed to mice carrying Cre recombinase driven by the nestin promoter. The resulting knockout mutant mouse brains were analyzed for changes in gene expression and alternative splicing. Knockout mice were compared to wildtype littermates. Whole mouse brain polyA plus RNA was isolated from three Nestin-cre knockout embryos at embryonic day 18 and compared to three wildtype littermates. RNA was converted to cDNA and used to probe Affymetrix MJAY splicing sensitive microarrays and analysed by Omniviewer to identify changes in splicing.
Project description:Injured sensory neurons activate a transcriptional program necessary for robust axon regeneration and eventual target reinnervation. Understanding the transcriptional regulators that govern this axon regenerative response may guide therapeutic strategies to promote axon regeneration in the injured nervous system. Here, we used cultured dorsal root ganglia neurons to identify pro-regenerative transcription factors. Using RNA sequencing, we first characterized this neuronal culture and determined that embryonic day 13.5 DRG (eDRG) neurons cultured for 7 days are similar to e15.5 DRG neurons in vivo and that all neuronal subtypes are represented. This eDRG neuronal culture does not contain other non-neuronal cell types. Next, we performed RNA sequencing at different time points after in vitro axotomy. Analysis of differentially expressed genes revealed upregulation of know regeneration associated transcription factors, including Jun Atf3 and Rest, paralleling the axon injury response in vivo. Analysis of transcription factor binding sites in differentially expressed genes revealed other known transcription factors promoting axon regeneration, such as Myc, Hif1a, Pparg, Ascl1a, Srf, as well as other transcription factors not yet characterized in axon regeneration. We next tested if overexpression of known and novel candidate transcription factors alone or in combination promote axon regeneration in vitro. Our results demonstrate that expression of Ctcf with Yy1 or E2f2 enhances in vitro axon regeneration. Our analysis reveals that pairs of transcription factors can functionally synergize to promote axon regeneration and highlight that transcription factor interaction play an important role as a regulator of axon regeneration.
Project description:Early neuronal development is a well-coordinated process in which neuronal stem cells differentiate into polarized neurons. This process has been well studied in classical non-human model systems, but to what extent this is recapitulated in human neurons remains unclear. To study neuronal polarization in human neurons, we cultured human iPSC-derived neurons, characterized early developmental stages, measured electrophysiological responses, and systematically profiled transcriptomic and proteomic dynamics during these steps. We found extensive remodeling of the neuron transcriptome and proteome, with altered mRNA expression of ~1,100 genes and different expression profiles of ~1,500 proteins during neuronal differentiation and polarization. We also identified a distinct stage in axon development marked by an increase in microtubule remodeling and apparent relocation of the axon initial segment from the distal to proximal axon. Our comprehensive characterization and quantitative map of transcriptome and proteome dynamics provides a solid framework for studying polarization in human neurons.
Project description:The splicing regulator PTBP2 controls a program of embryonic splicing required for neuronal maturation. The splicing regulatory proteins PTBP1 and PTBP2 show distinct temporal expression profiles in the developing brain. Neuronal progenitor cells predominantly express PTBP1, whereas developing neurons express high levels of PTBP2, which are subsequently reduced late in neuronal maturation. We show here that PTBP2 and the program of splicing it controls are essential to proper neuronal maturation and survival. To investigate its in vivo function, we generated conditional PTBP2 null alleles in mice. Loss of PTBP2 in neuronal progenitor cells leads to neonatal death without gross defects in brain architecture. Mice with specific depletion of PTBP2 in the cortex and forebrain are viable. However over the first three postnatal weeks, when the normal cortex expands and develops mature circuits, the PTBP2 null cortices degenerate. We find that PTBP2-/- neurons cultured from embryonic brain show the same initial viability as wild type cells with proper early marker expression and neurite outgrowth. Strikingly, between 10 and 20 days in culture PTBP2 null neurons undergo a catastrophic failure to mature and die. To assess the target transcripts leading to these phenotypes, we examined the genomewide splicing changes in the PTBP2 null brains. This identified a large number of mis-regulated exons that share a temporal pattern of regulation; in the absence of PTBP2 many isoforms normally found in adults are precociously expressed in the developing brain. Transcripts following this pattern encode essential neuronal proteins affecting neurite growth, pre- and post-synaptic assembly, and synaptic transmission. Our results define a new genetic regulatory program essential for neuronal survival and maturation, where PTBP2 acts to temporarily repress expression of protein isoforms until the final maturation of the neuron.
Project description:The splicing regulator PTBP2 controls a program of embryonic splicing required for neuronal maturation. The splicing regulatory proteins PTBP1 and PTBP2 show distinct temporal expression profiles in the developing brain. Neuronal progenitor cells predominantly express PTBP1, whereas developing neurons express high levels of PTBP2, which are subsequently reduced late in neuronal maturation. We show here that PTBP2 and the program of splicing it controls are essential to proper neuronal maturation and survival. To investigate its in vivo function, we generated conditional PTBP2 null alleles in mice. Loss of PTBP2 in neuronal progenitor cells leads to neonatal death without gross defects in brain architecture. Mice with specific depletion of PTBP2 in the cortex and forebrain are viable. However over the first three postnatal weeks, when the normal cortex expands and develops mature circuits, the PTBP2 null cortices degenerate. We find that PTBP2-/- neurons cultured from embryonic brain show the same initial viability as wild type cells with proper early marker expression and neurite outgrowth. Strikingly, between 10 and 20 days in culture PTBP2 null neurons undergo a catastrophic failure to mature and die. To assess the target transcripts leading to these phenotypes, we examined the genomewide splicing changes in the PTBP2 null brains. This identified a large number of mis-regulated exons that share a temporal pattern of regulation; in the absence of PTBP2 many isoforms normally found in adults are precociously expressed in the developing brain. Transcripts following this pattern encode essential neuronal proteins affecting neurite growth, pre- and post-synaptic assembly, and synaptic transmission. Our results define a new genetic regulatory program essential for neuronal survival and maturation, where PTBP2 acts to temporarily repress expression of protein isoforms until the final maturation of the neuron.