Conditional switching of KIF2A mutation provides new insights into cortical malformation pathogeny.

By using the Cre-mediated genetic switch technology, we were able to successfully generate a conditional knock-in mouse, bearing the KIF2A p.His321Asp missense point variant, identified in a subject with malformations of cortical development. These mice present with neuroanatomical anomalies and microcephaly associated with behavioral deficiencies and susceptibility to epilepsy, correlating with the described human phenotype. Using the flexibility of this model, we investigated RosaCre-, NestinCre- and NexCre-driven expression of the mutation to dissect the pathophysiological mechanisms underlying neurodevelopmental cortical abnormalities. We show that the expression of the p.His321Asp pathogenic variant increases apoptosis and causes abnormal multipolar to bipolar transition in newborn neurons, providing therefore insights to better understand cortical organization and brain growth defects that characterize KIF2A-related human disorders. We further demonstrate that the observed cellular phenotypes are likely to be linked to deficiency in the microtubule depolymerizing function of KIF2A.

ZMIZ1 Variants Cause a Syndromic Neurodevelopmental Disorder.

ZMIZ1 is a coactivator of several transcription factors, including p53, the androgen receptor, and NOTCH1. Here, we report 19 subjects with intellectual disability and developmental delay carrying variants in ZMIZ1. The associated features include growth failure, feeding difficulties, microcephaly, facial dysmorphism, and various other congenital malformations. Of these 19, 14 unrelated subjects carried de novo heterozygous single-nucleotide variants (SNVs) or single-base insertions/deletions, 3 siblings harbored a heterozygous single-base insertion, and 2 subjects had a balanced translocation disrupting ZMIZ1 or involving a regulatory region of ZMIZ1. In total, we identified 13 point mutations that affect key protein regions, including a SUMO acceptor site, a central disordered alanine-rich motif, a proline-rich domain, and a transactivation domain. All identified variants were absent from all available exome and genome databases. In vitro, ZMIZ1 showed impaired coactivation of the androgen receptor. In vivo, overexpression of ZMIZ1 mutant alleles in developing mouse brains using in utero electroporation resulted in abnormal pyramidal neuron morphology, polarization, and positioning, underscoring the importance of ZMIZ1 in neural development and supporting mutations in ZMIZ1 as the cause of a rare neurodevelopmental syndrome.

Ciliogenesis and cell cycle alterations contribute to KIF2A-related malformations of cortical development.

Genetic findings reported by our group and others showed that de novo missense variants in the KIF2A gene underlie malformations of brain development called pachygyria and microcephaly. Though KIF2A is known as member of the Kinesin-13 family involved in the regulation of microtubule end dynamics through its ATP dependent MT-depolymerase activity, how KIF2A variants lead to brain malformations is still largely unknown. Using cellular and in utero electroporation approaches, we show here that KIF2A disease-causing variants disrupts projection neuron positioning and interneuron migration, as well as progenitors proliferation. Interestingly, further dissection of this latter process revealed that ciliogenesis regulation is also altered during progenitors cell cycle. Altogether, our data suggest that deregulation of the coupling between ciliogenesis and cell cycle might contribute to the pathogenesis of KIF2A-related brain malformations. They also raise the issue whether ciliogenesis defects are a hallmark of other brain malformations, such as those related to tubulins and MT-motor proteins variants.

Homozygous Truncating Variants in TBC1D23 Cause Pontocerebellar Hypoplasia and Alter Cortical Development.

Pontocerebellar hypoplasia (PCH) is a heterogeneous group of rare recessive disorders with prenatal onset, characterized by hypoplasia of pons and cerebellum. Mutations in a small number of genes have been reported to cause PCH, and the vast majority of PCH cases are explained by mutations in TSEN54, which encodes a subunit of the tRNA splicing endonuclease complex. Here we report three families with homozygous truncating mutations in TBC1D23 who display moderate to severe intellectual disability and microcephaly. MRI data from available affected subjects revealed PCH, small normally proportioned cerebellum, and corpus callosum anomalies. Furthermore, through in utero electroporation, we show that downregulation of TBC1D23 affects cortical neuron positioning. TBC1D23 is a member of the Tre2-Bub2-Cdc16 (TBC) domain-containing RAB-specific GTPase-activating proteins (TBC/RABGAPs). Members of this protein family negatively regulate RAB proteins and modulate the signaling between RABs and other small GTPases, some of which have a crucial role in the trafficking of intracellular vesicles and are involved in neurological disorders. Here, we demonstrate that dense core vesicles and lysosomal trafficking dynamics are affected in fibroblasts harboring TBC1D23 mutation. We propose that mutations in TBC1D23 are responsible for a form of PCH with small, normally proportioned cerebellum and should be screened in individuals with syndromic pontocereballar hypoplasia.

Activation of Wnt/ß-catenin signaling is critical for the tumorigenesis of choroid plexus.

BACKGROUND: Choroid plexus (ChP) is the secretory epithelial structure located in brain ventricles. Choroid plexus tumors (CPTs) are rare neoplasms predominantly occurring in young patients with intensified malignancy in children. CPT treatment is hindered by insufficient knowledge of the tumor pathology and limited availability of valid models. METHODS: Genomic and transcriptomic data from CPT patients were analyzed to identify the putative pathological pathway. Cellular and molecular techniques were employed to validate bioinformatic results in CPT patient samples. Pharmacologic inhibition of Wnt/ß-catenin signaling was assessed in CPT cells. Cell-based assays of ChP cell lines were performed following CRISPR-Cas9-derived knockout and over-expression of Wnt/ß-catenin pathway genes. 3D CPT model was generated through CRISPR-Cas9-derived knockout of APC. RESULTS: We discovered that Wnt/ß-catenin signaling is activated in human CPTs, likely as a consequence of large-scale chromosomal instability events of the CPT genomes. We demonstrated that CPT-derived cells depend on autocrine Wnt/ß-catenin signaling for survival. Constitutive Wnt/ß-catenin pathway activation, either through knock-out of the negative regulator APC or overexpression of the ligand WNT3A, induced tumorigenic properties in ChP 2D in vitro models. Increased activation of Wnt/ß-catenin pathway in ChP organoids, through treatment with a potent GSK3ß inhibitor, reduced the differentiation of mature ChP epithelia cells. Remarkably, the depletion of APC was sufficient to induce the oncogenic transformation of ChP organoids. CONCLUSIONS: Our research identifies Wnt/ß-catenin signaling as a critical driver of CPT tumorigenesis and provides the first 3D in vitro model for future pathological and therapeutic studies of CPT.

CD44 expressed by myeloid cells promotes glioma invasion.

Glioblastoma multiforme (GBM) is one of the most common and malignant brain tumors in adulthood with a median survival of only 15 months. This poor prognosis is related to GBM's ability to extensively infiltrate the surrounding brain parenchyma resulting in diffuse spread of neoplastic cells in the brain, responsible for high rate of recurrence. CD44 (Cluster of Differentiation 44) is a transmembrane protein, overexpressed in multiple cancer types, including gliomas, and implicated in cell motility, proliferation and angiogenesis. Multiple studies have investigated the role of CD44 in GBM cells and have highlighted a link between tumor malignancy and CD44 expression. However up to date, little is known of the role of CD44 on cells from the tumor microenvironment (TME). Here, we have investigated a potential role of CD44 in the TME in regards to GBM invasiveness. Using an ex-vivo organotypic brain slice invasion assay, we show that absence of CD44 from the TME impairs the ability of glioma cells to invade the surrounding brain parenchyma. By deleting CD44 in the astrocytic, endothelial and myeloid compartments, we show that it is specifically CD44 expression in myeloid cells that is responsible for the observed phenotype. Combining in vivo studies in cell-specific knock-out mice and in vitro analyses on primary microglia we demonstrate that myeloid CD44 is implicated in Toll Like Receptor 2 signaling and is a major regulator of Matrix metalloproteinase 9 expression.

A Set of Cell Lines Derived from a Genetic Murine Glioblastoma Model Recapitulates Molecular and Morphological Characteristics of Human Tumors.

Glioblastomas (GBM) are the most aggressive tumors affecting the central nervous system in adults, causing death within, on average, 15 months after diagnosis. Immunocompetent in-vivo models that closely mirror human GBM are urgently needed for deciphering glioma biology and for the development of effective treatment options. The murine GBM cell lines currently available for engraftment in immunocompetent mice are not only exiguous but also inadequate in representing prominent characteristics of human GBM such as infiltrative behavior, necrotic areas, and pronounced tumor heterogeneity. Therefore, we generated a set of glioblastoma cell lines by repeated in vivo passaging of cells isolated from a neural stem cell-specific Pten/p53 double-knockout genetic mouse brain tumor model. Transcriptome and genome analyses of the cell lines revealed molecular heterogeneity comparable to that observed in human glioblastoma. Upon orthotopic transplantation into syngeneic hosts, they formed high-grade gliomas that faithfully recapitulated the histopathological features, invasiveness and immune cell infiltration characteristic of human glioblastoma. These features make our cell lines unique and useful tools to study multiple aspects of glioblastoma pathomechanism and to test novel treatments in an intact immune microenvironment.

TUBG1 missense variants underlying cortical malformations disrupt neuronal locomotion and microtubule dynamics but not neurogenesis.

De novo heterozygous missense variants in the γ-tubulin gene TUBG1 have been linked to human malformations of cortical development associated with intellectual disability and epilepsy. Here, we investigated through in-utero electroporation and in-vivo studies, how four of these variants affect cortical development. We show that TUBG1 mutants affect neuronal positioning, disrupting the locomotion of new-born neurons but without affecting progenitors' proliferation. We further demonstrate that pathogenic TUBG1 variants are linked to reduced microtubule dynamics but without major structural nor functional centrosome defects in subject-derived fibroblasts. Additionally, we developed a knock-in Tubg1Y92C/+ mouse model and assessed consequences of the mutation. Although centrosomal positioning in bipolar neurons is correct, they fail to initiate locomotion. Furthermore, Tubg1Y92C/+ animals show neuroanatomical and behavioral defects and increased epileptic cortical activity. We show that Tubg1Y92C/+ mice partially mimic the human phenotype and therefore represent a relevant model for further investigations of the physiopathology of cortical malformations.