Project description:The subcellular localization of specific mRNAs is an evolutionary conserved mechanism that underlies the establishment of cellular polarity and specialized cell functions. In neurons, mRNA trafficking and local protein translation in dendrites provides an important mechanism that mediates synaptic development and plasticity. The significance of mRNA targeting and protein synthesis in axons, however, is still unclear. Only a small number of transcripts have been identified in axons to date, and their contribution to axon growth and neuronal survival remains largely unknown. Here, we report the results of a novel screen that allowed the separate identification of mRNAs localized in cell bodies and in axons of developing neurons. Using compartmentalized cultures of sympathetic neurons and Sequential Analysis of Gene Expression (SAGE), the screen identified more than 200 axonal mRNAs, including ones that encode cytoskeletal proteins and proteins that function in neural development and signal transduction. Importantly, several classes of transcripts were selectively enriched in axons, indicating that an active process drives the targeting of specific mRNAs from the cell bodies to the axons. This study is the first comprehensive and unbiased analysis of mRNA localization in subcellular domains of any neuronal cell type. We used compartmentalized chambers to culture neonatal rat sympathetic neurons (Campenot, 1977). In these cultures, the cell bodies are separated from the distal axons by a 1 mm wide Teflon divider, which maintains the cell bodies and axon terminals in separate fluid compartments. Primary rat sympathetic neurons are especially suitable for compartmentalized culture because they can be grown as a highly homogeneous population without glial cells. Neurons were seeded in the central compartment with nerve growth factor (NGF), and after a few days, the NGF was lowered in this compartment and supplied only to the peripheral compartment to stimulate axon growth. The anti-mitotic agent cytosine arabinoside C (Ara-C) was added to both compartments to remove non-neuronal cells. mRNA was then isolated after 12 days in culture (DIV) from cell body or axon compartments. As the initial mRNA content in axons was not sufficient to perform the SAGE analysis, both axon and cell body mRNAs were subjected to two rounds of linear amplification to obtain antisense RNA (aRNA). The amplified aRNA was then reverse transcribed and second strand synthesis was performed to proceed with the SAGE assay using the LongSAGE kit (Invitrogen) according to the manufacturer’s protocol.
Project description:Sympathetic neurons were culture in compartmentalised chambers in medium with NGF (control condition). Cells were then subjected to NGF starvation for 18 hours followed by 1 hour of restimulation. Following a TRAP protocol, translating RNA was collected from either cell bodies (CB) or axons (Ax) from these neurons for RNA sequencing. Here, we find a strong compartmentalisation effect. We also find that only a few RNA are translated in restimulated distal axons within 1 hour compared with control condition axons.
Project description:Sympathetic neurons were culture in compartmentalised chambers in medium with NGF (control condition). Cells were then subjected to NGF starvation for 18 hours followed by 1 hour of restimulation. RNA was collected from either cell bodies (CB) or axons (Ax) from these neurons for meRIP-seq. Here, we find a strong compartmentalisation effect, in which RNA is hypermethylated in axons in both control and restimulated conditions. We also find that a select few RNA species are hypermethylated in restimulated axons compared to control axons, suggesting a fast time-dependent function for m6A marks in these RNAs.
Project description:The subcellular localization of specific mRNAs is an evolutionary conserved mechanism that underlies the establishment of cellular polarity and specialized cell functions. In neurons, mRNA trafficking and local protein translation in dendrites provides an important mechanism that mediates synaptic development and plasticity. The significance of mRNA targeting and protein synthesis in axons, however, is still unclear. Only a small number of transcripts have been identified in axons to date, and their contribution to axon growth and neuronal survival remains largely unknown. Here, we report the results of a novel screen that allowed the separate identification of mRNAs localized in cell bodies and in axons of developing neurons. Using compartmentalized cultures of sympathetic neurons and Sequential Analysis of Gene Expression (SAGE), the screen identified more than 200 axonal mRNAs, including ones that encode cytoskeletal proteins and proteins that function in neural development and signal transduction. Importantly, several classes of transcripts were selectively enriched in axons, indicating that an active process drives the targeting of specific mRNAs from the cell bodies to the axons. This study is the first comprehensive and unbiased analysis of mRNA localization in subcellular domains of any neuronal cell type.
Project description:Developing sympathetic neurons depend on nerve growth factor (NGF) for survival and die by apoptosis after NGF withdrawal. This process requires de novo gene expression but only a small number of genes induced by NGF deprivation have been identified so far. We have used Affymetrix Exon arrays to study the pattern of expression of all known genes in sympathetic neurons deprived of NGF. We identified 415 up- and 813 down-regulated genes, including most of the genes previously known to be regulated in this system. By including a mixed lineage kinase (MLK) inhibitor, CEP-11004, in our experimental design we identified which of the genes induced after NGF withdrawal are potential targets of the MLK-JNK-c-Jun pathway. A detailed Gene Ontology and functional enrichment analysis also identified genetic pathways, such as the ER unfolded protein response, that are highly enriched and overrepresented amongst the genes expressed after NGF withdrawal whilst hierarchical cluster analysis revealed four major patterns of gene expression. Five genes not previously studied in sympathetic neurons - trb3, ddit3, txnip, ndrg1 and mxi1 - were validated by real time-PCR. The proteins encoded by these genes also increased in level after NGF withdrawal and this increase was prevented by CEP-11004, suggesting that these genes are potential targets of the MLK-JNK-c-Jun pathway. Overall, our microarray data gives a comprehensive overview of, and provides new information about, signalling pathways and transcription factors that are regulated by NGF withdrawal and identifies potential targets of the MLK-JNK-c-Jun pathway in sympathetic neurons
Project description:Most cancers including pancreatic ductal adenocarcinoma (PDAC) are infiltrated by PNS neurons participating in their complex tumor microenvironment. However, their cell bodies and nuclei are located in the para- and pre-vertebral PNS ganglia located far from the tumor mass itself. Thus, molecular information on healthy organ- vs. cancer-infiltrating neurons is currently lacking in any sequencing dataset of healthy or tumor tissue. To specifically identify and molecularly characterize the identity and transcriptomes of PDAC-infiltrating neurons at single cell resolution, we developed “Trace-n-seq”. This method is based on retrograd tracing of axons from target tissues to their respective ganglia, followed by individual FACS-isolation and transcriptomic analysis. We characterized >2000 sympathetic and sensory neurons that infiltrate PDAC, healthy pancreas, or other abdominal organs.
Project description:Most cancers including pancreatic ductal adenocarcinoma (PDAC) are infiltrated by PNS neurons participating in their complex tumor microenvironment. However, their cell bodies and nuclei are located in the para- and pre-vertebral PNS ganglia located far from the tumor mass itself. Thus, molecular information on healthy organ- vs. cancer-infiltrating neurons is currently lacking in any sequencing dataset of healthy or tumor tissue. To specifically identify and molecularly characterize the identity and transcriptomes of PDAC-infiltrating neurons at single cell resolution, we developed “Trace-n-seq”. This method is based on retrograd tracing of axons from target tissues to their respective ganglia, followed by individual FACS-isolation and transcriptomic analysis. We characterized >2000 sympathetic and sensory neurons that infiltrate PDAC, healthy pancreas, or other abdominal organs.