Project description:During multicellular organization, individual cells need to constantly adjust intracellular contractility and junctional adhesive properties in order to maintain tissue cohesion and mechanotension. The membrane receptors linking external biochemical cues and internal cell mechanics are incompletely understood. Here, we reveal that the axon guidance receptor Plexin-B2 regulates intracellular mechanotension, and this in turn impacts cell-cell/cell-matrix adhesiveness during self-assembly of human embryonic stem cells (hESCs) and neuroprogenitor cells (hNPCs) into epithelial structures. The altered tissue mechanics caused by Plexin-B2 deficiency or over expression affects stem cell behaviors as well as β-catenin and YAP mechanosensing. Strikingly, Plexin-B2 deficiency results in accelerated neuronal differentiation, while proper levels of Plexin-B2 activity are required for maintaining cytoarchitectural integrity of the neuroepithelium as modeled in cerebral organoids. Mechanistically, Plexin-B2 engages its extracellular and Ras-GAP domains for mechanoregulation via RAP1/2. Our studies establish mechanoregulation as a key function of Plexin-B2 during multicellular organization, thereby solidifying the principle of force- mediated regulation of stem cell biology and tissue morphogenesis.
Project description:The diffuse invasion of glioblastoma (GBM) cells into healthy brain tissue is a main contributor for the high lethality of this most frequent form of malignant brain tumor. Plexins are cell surface receptors for semaphorins and control cell adhesion and cytoskeletal dynamics in development and in adult physiology. Gene expression of Plexin-B2 is upregulated in GBM and correlates with its lethality. We show here that Plexin-B2 activity can reduce the cohesiveness of GBM cells, which facilitates their invasive capacity. Targeted deletion of Plexin-B2 in GBM cells increased their cohesion to each other, revealing that a major function of Plexin-B2 activity is to downregulate cell-cell adhesion, possibly by downregulating other cell adhesion systems. In an in vivo intracranial transplant model, invasion of Plexin-B2 mutant GBM cells was impaired, with cells invading shorter distances. Interestingly, the loss of Plexin-B2 also changed the migration mode of cells, with the balance of cells in brain stroma vs. capillary space shifted: Plexin-B2 mutant cells were more likely to adhere to the vasculature. Our structure-function analyses revealed that the Ras-GAP domain of Plexin-B2 that is the main functional output responsible for the cohesion regulating function of Plexin-B2. Transcriptomic analyses of Plexin-B2 KO cells suggests that Plexin-B2 loss in different GBM cell lines has no direct transcriptional target genes, however, consistently, cell adhesion molecules were changed in expression, suggesting that cells compensate for loss of Plexin-B2. Thus, Plexin-B2 acts as a key regulator of the cohesiveness of GBM cells, thereby facilitating their invasiveness.
Project description:To identify Plexin-B2-associated proteins, articular chondrocytes were untreated or treated with Sema4D. Plexin-B2-bound proteins were purified by immunoprecipitation using an anti-Plexin-B2 antibody, followed by mass spectrometry.
Project description:Tissue repair after spinal cord injury (SCI) requires mobilization of immune and glial cells to form a protective barrier that seals the wound and facilitates debris clearing, inflammatory containment, and matrix compaction. This process involves corralling, wherein phagocytic immune cells become confined to the necrotic core surrounded by an astrocytic border. Here, we elucidate a temporally distinct gene signature in injury-activated microglia/macrophages (IAM), which engages axon guidance pathways. Plexin-B2 is upregulated in IAM, which is required for motosensory recovery after SCI. Plexin-B2 deletion in myeloid cells impairs corralling, leading to diffuse tissue damage, inflammatory spillover, and hampered axon regeneration. Corralling begins early and requires Plexin-B2 in both microglia and macrophages. Mechanistically, Plexin-B2 promotes microglia motility, steers IAM away from colliding cells, and facilitates matrix compaction. Our data thus establish Plexin-B2 as an important link that integrates biochemical cues and physical interactions of IAM with the injury microenvironment during wound healing.
Project description:CTCF plays a critical role in maintaining the three-dimensional (3D) chromatin organization, which is important for gene regulation, as it allows distal regulatory elements to come into proximity with one another. However, the detailed mechanism responsible for establishing and maintaining the recruitment of CTCF remains elusive. Here, we use in situ Hi-C to show that the ATP-dependent chromatin remodeler, Chd4, regulates intra-chromatin looping by controlling chromatin accessibility to conceal aberrant CTCF-binding sites in mouse embryonic stem cells (mESCs). These aberrant CTCF-binding sites are embedded in B2 SINEs and are localized within the interior of chromatin loops. In the absence of Chd4, the aberrant CTCF-binding sites become accessible and improper CTCF recruitment occurs, resulting in disorganization of the 3D chromatin architecture and subsequent disruption of enhancer-promoter interactions and the transcription of the corresponding genes. These results indicate that Chd4 regulates adequate transcription of mESCs by securing the proper 3D chromatin organization.
Project description:After central nervous system injury, a rapid neuroinflammatory response is induced. This response can be both beneficial and detrimental to neuronal survival in the first few days and increase the risk for neurodegeneration if it persists. Semaphorin4B (Sema4B), a transmembrane protein primarily expressed by cortical astrocytes, has been shown to play a role in neuronal cell death following injury. Our study shows that neuroinflammation is attenuated in Sema4B knockout mice and microglia/macrophage activation is reduced after cortical stab wound injury. In vitro, recombinant Sema4B enhances the activation of microglia following injury, suggesting astrocytic Sema4B functions as a ligand. Moreover, injury-induced activation of microglia is attenuated in the presence of Sema4B knockout astrocytes compared to heterozygous astrocytes. In vitro, experiments indicate Plexin-B2 is the Sema4B receptor on microglia. Consistent with this, microglia-specific Plexin-B2 knockout mice, similar to Sema4B knockout mice, also show a reduction in microglial activation after cortical injury. Finally, in Sema4B/Plexin-B2 double heterozygous mice, microglial activation is also reduced after injury, thus supporting the idea that both Sema4B and Plexin-B2 are part of the same signaling pathway. Taken together, we propose a model in which following injury, astrocytic Sema4B enhances the pro-inflammatory response of microglia/macrophages via Plexin-B2, leading to increased neuroinflammation.
Project description:Short interspersed nuclear elements (SINEs) are retrotransposons evolutionarily derived from endogenous RNA Polymerase III RNAs. Though SINE elements have undergone exaptation into gene regulatory elements, how transcribed SINE RNA impacts transcriptional and post-transcriptional regulation is largely unknown. This is partly due to a lack of information regarding which of the loci have transcriptional potential. Here, we present an approach (short interspersed nuclear element sequencing, SINE-seq), which selectively profiles RNA Polymerase III-derived SINE RNA, thereby identifying transcriptionally active SINE loci. Applying SINE-seq to monitor murine B2 SINE expression during a gammaherpesvirus infection revealed transcription from 28,270 SINE loci, with ~50% of active SINE elements residing within annotated RNA Polymerase II loci. Furthermore, B2 RNA can form intermolecular RNA-RNA interactions with complementary mRNAs, leading to nuclear retention of the targeted mRNA via a mechanism involving p54nrb. These findings illuminate a pathway for the selective regulation of mRNA export during stress via retrotransposon activation.