Search

Summary Extracellular vesicles (EVs) are released by most cell types but providing evidence for their physiological relevance remains challenging due to a lack of appropriate model organisms. Here, we developed an in vivo model to study EV function by expressing CD63-pHluorin in zebrafish embryos. A combination of imaging methods and proteomic analysis allowed us to study biogenesis, composition, transfer, uptake, and fate of individual endogenous EVs. We identified a subpopulation of EVs with exosome features, released in a syntenin-dependent manner from the yolk syncytial layer into the blood circulation. These exosomes are captured, endocytosed, and degraded by patrolling macrophages and endothelial cells in the caudal vein plexus (CVP) in a scavenger receptor- and dynamin-dependent manner. Interference with exosome biogenesis affected CVP growth, suggesting a role in trophic support. Altogether, our work represents a system for studying endogenous EV function in vivo with high spatiotemporal accuracy, demonstrating functional inter-organ communication by exosomes. Graphical Abstract Highlights • Single endogenous EVs can be live-visualized in the zebrafish embryo with CD63-pHluorin • Syntenin in the YSL regulates exosome release into the blood for further dissemination • YSL exosomes are taken up by macrophages and endothelial cells in the tail of the embryo • Uptake is scavenger receptor- and dynamin-dependent and provides trophic support Verweij et al. develop an in vivo model using zebrafish embryos to live-track the production, journey, and fate of individual exosomes. Using a combination of imaging methods and proteomic analysis, they investigate the composition of endogenous exosomes and the molecular mechanisms controlling their biogenesis, fates, and functions in receiving cells. [ABSTRACT FROM AUTHOR]

Summary Centrosome amplification has severe consequences during development and is thought to contribute to a variety of diseases such as cancer and microcephaly. However, the adverse effects of centrosome amplification in epithelia are still not known. Here, we investigate the consequences of centrosome amplification in the Drosophila wing disc epithelium. We found that epithelial cells exhibit mechanisms of clustering but also inactivation of extra centrosomes. Importantly, these mechanisms are not fully efficient, and both aneuploidy and cell death can be detected. Epithelial cells with extra centrosomes generate tumors when transplanted into WT hosts and inhibition of cell death results in tissue over-growth and disorganization. Using SILAC-fly, we found that Moesin, a FERM domain protein, is specifically upregulated in wing discs with extra centrosomes. Moesin localizes to the centrosomes and mitotic spindle during mitosis, and we show that Moesin upregulation influences extra-centrosome behavior and robust bipolar spindle formation. This study provides a mechanistic explanation for the increased aneuploidy and transformation potential primed by centrosome amplification in epithelial tissues. [ABSTRACT FROM AUTHOR]

Fine orchestration of excitatory and inhibitory synaptic development is required for normal brain function, and alterations may cause neurodevelopmental disorders. Using sparse molecular manipulations in intact brain circuits, we show that the glutamate receptor delta-1 (GluD1), a member of ionotropic glutamate receptors (iGluRs), is a postsynaptic organizer of inhibitory synapses in cortical pyramidal neurons. GluD1 is selectively required for the formation of inhibitory synapses and regulates GABAergic synaptic transmission accordingly. At inhibitory synapses, GluD1 interacts with cerebellin-4, an extracellular scaffolding protein secreted by somatostatin-expressing interneurons, which bridges postsynaptic GluD1 and presynaptic neurexins. When binding to its agonist glycine or D-serine, GluD1 elicits non-ionotropic postsynaptic signaling involving the guanine nucleotide exchange factor ARHGEF12 and the regulatory subunit of protein phosphatase 1 PPP1R12A. Thus, GluD1 defines a trans -synaptic interaction regulating postsynaptic signaling pathways for the proper establishment of cortical inhibitory connectivity and challenges the dichotomy between iGluRs and inhibitory synaptic molecules. • GluD1 mediates the formation and specification of inhibitory synapses in the cortex • GluD1 forms trans -synaptic interactions via Cbln4, a protein secreted by SST+ INs • GluD1 elicits agonist-dependent postsynaptic signaling via ARHGEF12 and PPP1R12A • GluD1 is a maverick iGluR operating through non-ionotropic mechanisms Fossati et al. show that, in stark contrast to other iGluRs, the glutamate receptor delta-1 (GluD1) operates at inhibitory, rather than excitatory, synapses in the cortex. GluD1 mediates trans -synaptic signaling governing the formation of synapses between specific interneurons and pyramidal neurons. [ABSTRACT FROM AUTHOR]

The current consensus recognizes four main medulloblastoma subgroups (wingless, Sonic hedgehog, group 3 and group 4). While medulloblastoma subgroups have been characterized extensively at the (epi-)genomic and transcriptomic levels, the proteome and phosphoproteome landscape remain to be comprehensively elucidated. Using quantitative (phospho)-proteomics in primary human medulloblastomas, we unravel distinct posttranscriptional regulation leading to highly divergent oncogenic signaling and kinase activity profiles in groups 3 and 4 medulloblastomas. Specifically, proteomic and phosphoproteomic analyses identify aberrant ERBB4-SRC signaling in group 4. Hence, enforced expression of an activated SRC combined with p53 inactivation induces murine tumors that resemble group 4 medulloblastoma. Therefore, our integrative proteogenomics approach unveils an oncogenic pathway and potential therapeutic vulnerability in the most common medulloblastoma subgroup., (Copyright © 2018 Elsevier Inc. All rights reserved.)

The ventricular zone (VZ) of the developing cerebral cortex is a pseudostratified epithelium that contains progenitors undergoing precisely regulated divisions at its most apical side, the ventricular lining (VL). Mitotic perturbations can contribute to pathological mechanisms leading to cortical malformations. The HeCo mutant mouse exhibits subcortical band heterotopia (SBH), likely to be initiated by progenitor delamination from the VZ early during corticogenesis. The causes for this are however, currently unknown. Eml1, a microtubule (MT)-associated protein of the EMAP family, is impaired in these mice. We first show that MT dynamics are perturbed in mutant progenitor cells in vitro. These may influence interphase and mitotic MT mechanisms and indeed, centrosome and primary cilia were altered and spindles were found to be abnormally long in HeCo progenitors. Consistently, MT and spindle length regulators were identified in EML1 pulldowns from embryonic brain extracts. Finally, we found that mitotic cell shape is also abnormal in the mutant VZ. These previously unidentified VZ characteristics suggest altered cell constraints which may contribute to cell delamination.