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Astroblastomas (ABs) are rare brain tumors of unknown origin. We performed an integrative genetic and epigenetic analysis of AB-like tumors. Here, we show that tumors traceable to neural stem/progenitor cells (radial glia) that emerge during early to later brain development occur in children and young adults, respectively. Tumors with MN1-BEND2 fusion appear to present exclusively in females and exhibit overexpression of genes expressed prior to 25 post-conception weeks (pcw), including genes enriched in early ventricular zone radial glia and ependymal tumors. Other, histologically classic ABs overexpress or harbor mutations of mitogen-activated protein kinase pathway genes, outer and truncated radial glia genes, and genes expressed after 25 pcw, including neuronal and astrocyte markers. Findings support that AB-like tumors arise in the context of epigenetic and genetic changes in neural progenitors. Selective gene fusion, variable imprinting and/or chromosome X-inactivation escape resulting in biallelic overexpression may contribute to female predominance of AB molecular subtypes. Astroblastoma (AB) is an uncommon brain tumour and its origin remains unknown. Here, the authors perform integrative molecular analysis of 35 AB-like tumours and provide evidence that these arise in the context of epigenetic and genetic changes in neural progenitors occurring during brain development. [ABSTRACT FROM AUTHOR]

Exon junction complexes (EJCs) mark untranslated spliced mRNAs and are crucial for the mRNA lifecycle. An imbalance in EJC dosage alters mouse neural stem cell (mNSC) division and is linked to human neurodevelopmental disorders. In quiescent mNSC and immortalized human retinal pigment epithelial (RPE1) cells, centrioles form a basal body for ciliogenesis. Here, we report that EJCs accumulate at basal bodies of mNSC or RPE1 cells and decline when these cells differentiate or resume growth. A high-throughput smFISH screen identifies two transcripts accumulating at centrosomes in quiescent cells, NIN and BICD2. In contrast to BICD2, the localization of NIN transcripts is EJC-dependent. NIN mRNA encodes a core component of centrosomes required for microtubule nucleation and anchoring. We find that EJC down-regulation impairs both pericentriolar material organization and ciliogenesis. An EJC-dependent mRNA trafficking towards centrosome and basal bodies might contribute to proper mNSC division and brain development. Exon junction complexes (EJCs) that mark untranslated mRNA are involved in transport, translation and nonsense-mediated mRNA decay. Here the authors show centrosomal localization of EJCs which appears to be required for both the localization of NIN mRNA around centrosomes and ciliogenesis. [ABSTRACT FROM AUTHOR]

Multiciliated ependymal cells line all brain cavities. The beating of their motile cilia contributes to the flow of cerebrospinal fluid, which is required for brain homoeostasis and functions. Motile cilia, nucleated from centrioles, persist once formed and withstand the forces produced by the external fluid flow and by their own cilia beating. Here, we show that a dense actin network around the centrioles is induced by cilia beating, as shown by the disorganisation of the actin network upon impairment of cilia motility. Moreover, disruption of the actin network, or specifically of the apical actin network, causes motile cilia and their centrioles to detach from the apical surface of ependymal cell. In conclusion, cilia beating controls the apical actin network around centrioles; the mechanical resistance of this actin network contributes, in turn, to centriole stability. [ABSTRACT FROM AUTHOR]

Adult neurogenesis in the mammalian brain is restricted to specific regions, such as the dentate gyrus (DG) in the hippocampus and the subventricular zone (SVZ) in the walls of the lateral ventricles. Here, we used a mouse line carrying a knock-in of Cre recombinase in the Prss56 gene, in combination with two Cre-inducible fluorescent reporters ( Rosa26 and Rosa26 ), to perform genetic tracing of Prss56-expressing cells in the adult brain. We found reporter-positive cells in three neurogenic niches: the DG, the SVZ and the hypothalamus ventricular zone. In the prospective DG, Prss56 is expressed during embryogenesis in a subpopulation of radial glia. The pattern of migration and differentiation of reporter-positive cells during development recapitulates the successive steps of DG neurogenesis, including the formation of a subpopulation of adult neural stem cells (NSC). In the SVZ, Prss56 is expressed postnatally in a subpopulation of adult NSC mainly localized in the medial-ventral region of the lateral wall. This subpopulation preferentially gives rise to deep granule and Calbindin-positive periglomerular interneurons in the olfactory bulb. Finally, Prss56 is also expressed in a subpopulation of α2-tanycytes, which are potential adult NSCs of the hypothalamus ventricular zone. Our observations suggest that some α2-tanycytes translocate their soma into the parenchyma and may give rise to a novel cell type in this territory. Overall, this study establishes the Prss56 line as an efficient and promising new tool to study multiple aspects of adult neurogenesis in the mouse. [ABSTRACT FROM AUTHOR]

The semi-conservative centrosome duplication in cycling cells gives rise to a centrosome composed of a mother and a newly formed daughter centriole. Both centrioles are regarded as equivalent in their ability to form new centrioles and their symmetric duplication is crucial for cell division homeostasis. Multiciliated cells do not use the archetypal duplication program and instead form more than a hundred centrioles that are required for the growth of motile cilia and the efficient propelling of physiological fluids. The majority of these new centrioles are thought to appear de novo, that is, independently from the centrosome, around electron-dense structures called deuterosomes. Their origin remains unknown. Using live imaging combined with correlative super-resolution light and electron microscopy, we show that all new centrioles derive from the pre-existing progenitor cell centrosome through multiple rounds of procentriole seeding. Moreover, we establish that only the daughter centrosomal centriole contributes to deuterosome formation, and thus to over ninety per cent of the final centriole population. This unexpected centriolar asymmetry grants new perspectives when studying cilia-related diseases and pathological centriole amplification observed in cycling cells and associated with microcephaly and cancer. [ABSTRACT FROM AUTHOR]

In mammals, motile cilia cover many organs, such as fallopian tubes, respiratory tracts and brain ventricles. The development and function of these organs critically depend on efficient directional fluid flow ensured by the alignment of ciliary beating. To identify the mechanisms involved in this process, we analysed motile cilia of mouse brain ventricles, using biophysical and molecular approaches. Our results highlight an original orientation mechanism for ependymal cilia whereby basal bodies first dock apically with random orientations, and then reorient in a common direction through a coupling between hydrodynamic forces and the planar cell polarity (PCP) protein Vangl2, within a limited time-frame. This identifies a direct link between external hydrodynamic cues and intracellular PCP signalling. Our findings extend known PCP mechanisms by integrating hydrodynamic forces as long-range polarity signals, argue for a possible sensory role of ependymal cilia, and will be of interest for the study of fluid flow-mediated morphogenesis. [ABSTRACT FROM AUTHOR]

Neural stem cells that continue to produce neurons are retained in the adult hippocampal dentate gyrus. The mechanisms by which embryonic neural progenitors expand and transform into postnatal neural stem cells, an essential process for the continual production of neurons throughout life, remain unknown. We found that radial astrocytes, the postnatal progenitors in the dentate gyrus, failed to develop after embryonic ablation of ciliary genes or Smoothened (Smo), an essential component for Sonic hedgehog (Shh) signaling. Postnatal dentate neurogenesis failed in these mutant mice, and the dentate gyrus became severely hypotrophic. In contrast, expression of a constitutively active Smo (SmoM2-YFP) resulted in a marked expansion of the dentate gyrus. Double-mutant analyses suggested that both wild-type Smo and SmoM2-YFP function through the primary cilia. We conclude that Shh signaling, acting through the primary cilia, has a critical role in the expansion and establishment of postnatal hippocampal progenitors. [ABSTRACT FROM AUTHOR]

Cell biology relies largely on reproducible visual observations. Unlike cell culture, tissues are heterogeneous, making difficult the collection of biological replicates that would spotlight a precise location. In consequence, there is no standard approach for estimating the statistical significance of an observed pattern in a tissue sample. Here, we introduce SET (for Synthesis of Epithelial Tissue), a method that can accurately reconstruct the cell tessellation formed by an epithelium in a microscopy image as well as thousands of alternative synthetic tessellations made of the exact same cells. SET can build an accurate null distribution to statistically test if any local pattern is necessarily the result of a process, or if it could be explained by chance in the given context. We provide examples in various tissues where visible, and invisible, cell and subcellular patterns are unraveled in a statistically significant manner using a single image and without any parameter settings. Laruelle et al. present a fitting based computational method called SET that can detect hidden spatial structure in cell tissue organization in a statistically significant manner using a single image and without any parameter settings. They exemplify the utility of the approach by identifying invisible cell and subcellular patterns. [ABSTRACT FROM AUTHOR]

Reproductive and respiratory organs, along with brain ventricles, are lined by multiciliated epithelial cells (MCC) that generate cilia-powered fluid flows. MCC hijack the centrosome duplication pathway to form hundreds of centrioles and nucleate motile cilia. In these cells, the large majority of procentrioles are formed associated with partially characterized organelles called deuterosomes. We recently challenged the paradigm that deuterosomes and procentrioles are formed de novo by providing data, in brain MCC, suggesting that they are nucleated from the pre-existing centrosomal younger centriole. However, the origin of deuterosomes and procentrioles is still under debate. Here, we further question centrosome importance for deuterosome and centriole amplification. First, we provide additional data confirming that centriole amplification occurs sequentially from the centrosomal region, and that the first procentriole-loaded deuterosomes are associated with the daughter centriole or in the centrosomal centriole vicinity. Then, to further test the requirement of the centrosome in deuterosome and centriole formation, we depleted centrosomal centrioles using a Plk4 inhibitor. We reveal unexpected limited consequences in deuterosome/centriole number in absence of centrosomal centrioles. Notably, in absence of the daughter centriole only, deuterosomes are not seen associated with the mother centriole. In absence of both centrosomal centrioles, procentrioles are still amplified sequentially and with no apparent structural defects. They seem to arise from a focal region, characterized by microtubule convergence and pericentriolar material (PCM) assembly. The relevance of deuterosome association with the daughter centriole as well as the role of the PCM in the focal and sequential genesis of centrioles in absence of centrosomal centrioles are discussed. [ABSTRACT FROM AUTHOR]

Three-dimensional fluorescence microscopy followed by image processing is routinely used to study biological objects at various scales such as cells and tissue. However, maximum intensity projection, the most broadly used rendering tool, extracts a discontinuous layer of voxels, obliviously creating important artifacts and possibly misleading interpretation. Here we propose smooth manifold extraction, an algorithm that produces a continuous focused 2D extraction from a 3D volume, hence preserving local spatial relationships. We demonstrate the usefulness of our approach by applying it to various biological applications using confocal and wide-field microscopy 3D image stacks. We provide a parameter-free ImageJ/Fiji plugin that allows 2D visualization and interpretation of 3D image stacks with maximum accuracy. [ABSTRACT FROM AUTHOR]