Endosomal trafficking defects alter neural progenitor proliferation and cause microcephaly

Primary microcephaly and megalencephaly are severe brain malformations defined by reduced and increased brain size, respectively. Whether these two pathologies arise from related alterations at the molecular level is unclear. Microcephaly has been largely associated with centrosomal defects, leading to cell death. Here, we investigate the consequences of WDR81 loss of function, which causes severe microcephaly in patients. We show that WDR81 regulates endosomal trafficking of EGFR and that loss of function leads to reduced MAP kinase pathway activation. Mouse radial glial progenitor cells knocked-out for WDR81 exhibit reduced proliferation rate, subsequently leading to reduced brain size. These proliferation defects are rescued in vivo by expressing a megalencephaly-causing mutant form of Cyclin D2. Our results identify the endosomal machinery as an important regulator of proliferation rates and brain growth, demonstrating that microcephaly and megalencephaly can be caused by opposite effects on the proliferation rate of radial glial progenitors.

Intracardial perfusion of the African turquoise killifish v1

This perfusion protocol is essential for preserving tissue morphology in order to perform good quality immunohistochemical stainings. Here, we show you how we perform our perfusions on the African turquoise killifish. This protocol was already used in the following publications: Aging impairs the essential contributions of non-glial progenitors to neurorepair in the dorsal telencephalon of the Killifish Nothobranchius furzeri - PubMed (nih.gov) Single-cell sequencing of the adult killifish (N. furzeri) brain identifies an atypical progenitor, glial and neuronal heterogeneity | bioRxiv

The polarity protein Par3 coordinates positively self-renewal and negatively invasiveness in glioblastoma

Glioblastoma (GBM) is a brain malignancy characterized by invasiveness to the surrounding brain tissue and by stem-like cells, which propagate the tumor and may also regulate invasiveness. During brain development, polarity proteins, such as Par3, regulate asymmetric cell division of neuro-glial progenitors and neurite motility. We, therefore, studied the role of the Par3 protein (encoded by PARD3) in GBM. GBM patient transcriptomic data and patient-derived culture analysis indicated diverse levels of expression of PARD3 across and independent from subtypes. Multiplex immunolocalization in GBM tumors identified Par3 protein enrichment in SOX2-, CD133-, and NESTIN-positive (stem-like) cells. Analysis of GBM cultures of the three subtypes (proneural, classical, mesenchymal), revealed decreased gliomasphere forming capacity and enhanced invasiveness upon silencing Par3. GBM cultures with suppressed Par3 showed low expression of stemness (SOX2 and NESTIN) but higher expression of differentiation (GFAP) genes. Moreover, Par3 silencing reduced the expression of a set of genes encoding mitochondrial enzymes that generate ATP. Accordingly, silencing Par3 reduced ATP production and concomitantly increased reactive oxygen species. The latter was required for the enhanced migration observed upon silencing of Par3 as anti-oxidants blocked the enhanced migration. These findings support the notion that Par3 exerts homeostatic redox control, which could limit the tumor cell-derived pool of oxygen radicals, and thereby the tumorigenicity of GBM.

Oligodendrocyte precursor cells prune axons in the mouse neocortex

Neurons in the developing brain undergo extensive structural refinement as nascent circuits adopt their mature form. This transformation is facilitated by the engulfment and degradation of excess axonal branches and inappropriate synapses by surrounding glial cells, including microglia and astrocytes. However, the small size of phagocytic organelles and the complex, highly ramified morphology of glia has made it difficult to determine the contribution of these and other glial cell types to this process. Here, we used large scale, serial electron microscopy (ssEM) with computational volume segmentation to reconstruct the complete 3D morphologies of distinct glial types in the mouse visual cortex. Unexpectedly, we discovered that the fine processes of oligodendrocyte precursor cells (OPCs), a population of abundant, highly dynamic glial progenitors, frequently surrounded terminal axon branches and included numerous phagolysosomes (PLs) containing fragments of axons and presynaptic terminals. Single- nucleus RNA sequencing indicated that cortical OPCs express key phagocytic genes, as well as neuronal transcripts, consistent with active axonal engulfment. PLs were ten times more abundant in OPCs than in microglia in P36 mice, and declined with age and lineage progression, suggesting that OPCs contribute very substantially to refinement of neuronal circuits during later phases of cortical development.

Angiopoietin 1 and integrin beta 1b are vital for zebrafish brain development

This study aimed at identifying the role of angiopoietin 1 (angpt1) in brain development, the mode of action of angpt1, and the main targets in the zebrafish brain. We investigated embryonic brain angiogenesis and neural development in theangpt1sa14264,itgb1bmi371,tekhu1667mutant fish, and the effects of transgenic overexpression ofangpt1in the larval brain. Lack ofangpt1was associated with downregulation oftekand upregulation ofitgb1b. We found deficiencies in the patterning of proliferation, the vascular network and reticulospinal neurons in the hindbrain, and selective deficiencies in specific neurotransmitter systems. In theangpt1sa14264anditgb1bmi371larval brains, using microangiography, retrograde labeling, and immunostaining, we demonstrated that the targeted destruction ofangpt1sa14264anditgb1bmi371mutant fish caused severe irregular cerebrovascular development, aberrant hindbrain patterning, downregulation of neural proliferation, expansion of the radial glial progenitors, deficiencies of dopaminergic, histaminergic, and GABAergic populations in the larval brain. In contrast, thetekhu1667mutants regularly grew with no such apparent phenotypes. Neurally overexpressedangpt1promoted opposite effects by increasing the vascular branching, increasing cell proliferation, and neuronal progenitors. Notably, zebrafishangpt1showed neurogenic activity independent of its typical receptortek, indicating the novel role of a dual regulation byangpt1in embryonic neurogenesis and angiogenesis in zebrafish. The results show that angpt1 and its interaction with itgb1b are crucial in zebrafish brain neuronal and vascular development and suggest that angpt1 through itgb1b can act as a neurogenic factor in the neural proliferation fate in the developing brain.

Aging impairs the essential contributions of non-glial progenitors to neurorepair in the dorsal telencephalon of the Killifish N. furzeri

SummaryThe aging central nervous system (CNS) of mammals displays progressive limited regenerative abilities. Recovery after loss of neurons is extremely restricted in the aged brain. Many research models fall short in recapitulating mammalian aging hallmarks or have an impractically long lifespan. We established a traumatic brain injury model in the African turquoise killifish (Nothobranchius furzeri), a regeneration-competent vertebrate model that evolved to naturally age extremely fast. Stab-wound injury of the aged killifish dorsal telencephalon unveils an impaired and incomplete regeneration response when compared to young individuals. Remarkably, killifish brain regeneration is mainly supported by atypical non-glial progenitors, yet their proliferation capacity appears declined with age. We identified a high inflammatory response and glial scarring to also underlie the hampered generation of new neurons in aged fish. These primary results will pave the way for further research to unravel the factor age in relation to neurorepair, and to improve therapeutic strategies to restore the injured and/or diseased aged mammalian CNS.HighlightsAging impairs neurorepair in the killifish pallium at multiple stages of the regeneration processAtypical non-glial progenitors support the production of new neurons in the naive and injured dorsal palliumThe impaired regeneration capacity of aged killifish is characterized by a reduced reactive proliferation of these progenitors followed by a decreased generation of newborn neurons that in addition, fail to reach the injury siteExcessive inflammation and glial scarring surface as potential brakes on brain repair in the aged killifish pallium