Project description:The myelin sheaths that surround the thick axons of the peripheral nervous system are produced by the highly specialized Schwann cells. Differentiation of Schwann cells and myelination occur in discrete steps. Each of these requires coordinated expression of specific proteins in a precise sequence, yet the regulatory mechanisms controlling protein expression during these events are incompletely understood. Here we report that Schwann cell-specific ablation of the enzyme Dicer1, which is required for the production of small non-coding regulatory microRNAs, fully arrests Schwann cell differentiation, resulting in early postnatal lethality. Dicer-/- Schwann cells had lost their ability to myelinate, yet were still capable of sorting axons. Both cell death and, paradoxically, proliferation of immature Schwann cells was vastly enhanced, suggesting that their terminal differentiation is triggered by growth-arresting regulatory microRNAs. Using microRNA microarrays, we identified 16 miRNAs that are upregulated upon myelination and whose expression is controlled by Dicer in Schwann cells. This set of microRNAs appears to drive Schwann cell differentiation and myelination of peripheral nerves, thereby fulfilling a crucial function for survival of the organism. Samples representing Schwann cell-specific ablation of the enzyme Dicer1 and wild type controls at developmental stages E17 and P4. Geometric mean-averaged data linked below as supplementary file.
Project description:The myelin sheaths that surround the thick axons of the peripheral nervous system are produced by the highly specialized Schwann cells. Differentiation of Schwann cells and myelination occur in discrete steps. Each of these requires coordinated expression of specific proteins in a precise sequence, yet the regulatory mechanisms controlling protein expression during these events are incompletely understood. Here we report that Schwann cell-specific ablation of the enzyme Dicer1, which is required for the production of small non-coding regulatory microRNAs, fully arrests Schwann cell differentiation, resulting in early postnatal lethality. Dicer-/- Schwann cells had lost their ability to myelinate, yet were still capable of sorting axons. Both cell death and, paradoxically, proliferation of immature Schwann cells was vastly enhanced, suggesting that their terminal differentiation is triggered by growth-arresting regulatory microRNAs. Using microRNA microarrays, we identified 16 miRNAs that are upregulated upon myelination and whose expression is controlled by Dicer in Schwann cells. This set of microRNAs appears to drive Schwann cell differentiation and myelination of peripheral nerves, thereby fulfilling a crucial function for survival of the organism.
Project description:Myelination is essential for nervous system function. Schwann cells interact with neurons and with the basal lamina to sort and myelinate axons, using known receptors and signaling pathways. In contrast, the transcriptional control of axonal sorting and the role of mechano-transduction in myelination are largely unknown. Yap and Taz are effectors of the Hippo pathway that integrate chemical and mechanical signals in cells. Here, we describe a previously unknown role for the Hippo pathway in myelination. Using conditional mutagenesis in mice we show that Taz is required in Schwann cells for radial sorting and myelination. Yap is redundant with Taz as ablation of both Yap and Taz abolishes radial sorting. Yap/Taz regulate Schwann cell proliferation and transcription of basal lamina receptors, both necessary for proper radial sorting of axons, and subsequent myelination. These data link transcriptional effectors of the Hippo pathway and of mechanotransduction to myelin formation in Schwann cells.
Project description:Elucidating the genes regulated during cell-cell communication remains fascinating considering the importance of cell recognition and downstream signaling through development and in many diseases. In the peripheral nervous system, the interaction between Schwann cells (SCs) and axons is crucial as it allows their survival and induces SCs to differentiate and engage a process of myelination. To get further insight the molecular mechanisms resulting from this cell interaction, comparative gene analysis between SCs and SCs co-cultured with DRG neurons were performed and led us to identify a set of 32 genes regulated in SCs in the early stage of neuron-SC contact. Expression of several candidates were analyzed by QPCR during development and we demonstrate using a blocking antibody approach in an in vitro myelination assay that one candidate was not only upregulated in response to axonal contact but also controls peripheral myelination. Three biological replicates each in dye swap for 22k slides and two biological replicates each in dye swap for NeuroDev2
Project description:We addressed the requirement of DGCR8, DROSHA and DICER functions in developing and adult Schwann cells (SCs) using mouse mutants. We found that the microprocessor components DGCR8 and DROSHA are crucial for axonal radial sorting and to establish correct SC numbers upon myelination. Transcriptome analysis revealed that the microprocessor is essential to prevent aberrant accumulation and de novo expression of injury-response genes. Those genes are predicted targets of stage-specifically enriched miRNAs. In agreement, DGCR8 and DICER are required for proper maintenance of the myelinated SC state. We conclude that the miRNA pathway is crucial for preventing inappropriate activity of injury response genes in developing and adult SCs.
Project description:Activation of mTOR signaling by Tsc1 ablation during early developmental stages increases SC proliferation and delays radial sorting, while causing hypomyelination in the PNS. However, knockout Tsc1 in myelinating SCs at postnatal stages promotes myelin overgrowth and outfoldings. Sustained mTOR pathway leads to activation of the PLK signaling pathway. mTOR attenuation or pharmacological inhibition of PLK1 could partially rescue myelination defects in Tsc1 mutant sciatic nerves. Our data suggest that TSC1-mTOR maintains the homeostasis of SC proliferation and differentiation in a stage-specific manner.
Project description:Schwann cell (SC) myelination in the peripheral nervous system is essential for motor function, and uncontrolled SC proliferation occurs in cancer. Here, we show that a dual direct role for Hippo effectors TAZ and YAP in regulation of SC proliferation and myelination through modulating G protein expression and interacting with SOX10, respectively. Developmentally-regulated mutagenesis indicates that TAZ/YAP are critical for SC proliferation yet also required for their differentiation and myelination. Genome-wide occupancy mapping and transcriptome profiling reveal that nuclear TAZ and YAP promote SC proliferation by activating cell cycle regulators, while targeting critical differentiation regulators in cooperation with SOX10 for myelination. We further identified that TAZ targets and represses Gnas, encoding Gαs-protein, which opposes TAZ/YAP activities to decelerate proliferation. Gnas deletion expands SC precursor pools and blocks myelination in the sciatic nerve. Thus, our study revealed that the Hippo/TAZ/YAP and Gαs-protein feedback circuit functions as a fulcrum balancing SC proliferation and differentiation, providing insights into molecular programming of SC lineage progression and homeostasis.
Project description:Cells need to integrate chemical and physical signals into transcriptional programs. In the peripheral nerves, axonal caliber selection by specialized Schwann cells, is critical for developmental myelination. However, only mechanisms through which Schwann cells sense chemical signals are well characterized. We identify ACtin-Like protein 6a (ACTL6a), a component of the SWI/SNF chromatin remodeling complex, as critical for axonal caliber recognition and developmental myelination. ACTL6a is expressed in the developing nerve and, when activated by contact with axons or nanofibers of specific caliber, it promotes the eviction of repressive histone marks thereby enhancing the transcriptional program of myelination. Mutant mice with Schwann cells lacking ACTL6a display aberrant recognition of axonal caliber, resulting in defective radial sorting and lower levels of transcripts regulating myelination of developing nerves. We suggest that developing peripheral nerves require an ACTL6a-dependent integration of physical and chemical signals in Schwann cells to release of repressive histone modifications and promote myelination.