Identity and nature of neural stem cells in the adult human subventricular zone

The existence of neural stem cells (NSCs) in adult human brain neurogenic regions remains unresolved. To address this, we created a cell atlas of the adult human subventricular zone (SVZ) derived from fresh neurosurgical samples using single-cell transcriptomics. We discovered 2 adult radial glia (RG)-like populations, aRG1 and aRG2. aRG1 shared features with fetal early RG (eRG) and aRG2 were transcriptomically similar to fetal outer RG (oRG). We also captured early neuronal and oligodendrocytic NSC states. We found that the biological programs driven by their transcriptomes support their roles as early lineage NSCs. Finally, we show that these NSCs have the potential to transition between states and along lineage trajectories. These data reveal that multipotent NSCs reside in the adult human SVZ.

Glioblastoma scRNAseq Shows Treatment-induced, Immune-dependent Rise In Mesenchymal Cancer Cells, and Structural Variants in Distal Neural Stem Cells

BACKGROUND

Glioblastoma is a treatment-resistant brain cancer. Its hierarchical cellular nature and its tumour microenvironment (TME) before, during, and after treatments remain unresolved.

METHODS

Here, we used single-cell RNA-sequencing to analyze new and recurrent glioblastoma, and the nearby subventricular zone (SVZ).

RESULTS

We found four glioblastoma neural lineages are present in new and recurrent glioblastoma with an enrichment of the cancer mesenchymal lineage, immune cells, and reactive astrocytes in early recurrences. Cancer lineages were hierarchically organized around cycling oligodendrocytic and astrocytic progenitors that are transcriptomically similar but distinct to SVZ neural stem cells (NSCs). Furthermore, NSCs from the SVZ of glioblastoma patients harbored glioblastoma chromosomal anomalies. Lastly, mesenchymal cancer cells and TME reactive astrocytes shared similar gene signatures which were induced by radiotherapy in a myeloid-dependent fashion in vivo.

CONCLUSION

These data reveal the dynamic, immune-dependent nature of glioblastoma's response to treatments and identify distant NSCs as likely cells of origin.

Single-cell RNA-seq reveals that glioblastoma recapitulates a normal neurodevelopmental hierarchy

Cancer stem cells are critical for cancer initiation, development, and treatment resistance. Our understanding of these processes, and how they relate to glioblastoma heterogeneity, is limited. To overcome these limitations, we performed single-cell RNA sequencing on 53586 adult glioblastoma cells and 22637 normal human fetal brain cells, and compared the lineage hierarchy of the developing human brain to the transcriptome of cancer cells. We find a conserved neural tri-lineage cancer hierarchy centered around glial progenitor-like cells. We also find that this progenitor population contains the majority of the cancer's cycling cells, and, using RNA velocity, is often the originator of the other cell types. Finally, we show that this hierarchal map can be used to identify therapeutic targets specific to progenitor cancer stem cells. Our analyses show that normal brain development reconciles glioblastoma development, suggests a possible origin for glioblastoma hierarchy, and helps to identify cancer stem cell-specific targets.

Identification and characterization of a novel chemically induced allele at the planar cell polarity gene Vangl2

Planar cell polarity (PCP) signaling controls a number of morphogenetic processes including convergent extension during gastrulation and neural tube formation. Defects in this pathway cause neural tube defects (NTD), the most common malformations of the central nervous system. The Looptail (Lp) mutant mouse was the first mammalian mutant implicating a PCP gene (Vangl2) in the pathogenesis of NTD. We report on a novel chemically induced mutant allele at Vangl2 called Curly Bob that causes a missense mutation p.Ile268Asn (I268N) in the Vangl2 protein. This mutant segregates in a semi-dominant fashion with heterozygote mice displaying a looped tail appearance, bobbing head, and a circling behavior. Homozygote mutant embryos suffer from a severe form of NTD called craniorachischisis, severe PCP defects in the inner hair cells of the cochlea and posterior cristae, and display a distinct defect in retinal axon guidance. This mutant genetically interacts with the Lp allele (Vangl2 ^S464N ) in neural tube development and inner ear hair cell polarity. The Vangl2^I268N protein variant is expressed at very low levels in affected neural and retinal tissues of mutant homozygote embryos. Biochemical studies show that Vangl2^I268N exhibits impaired targeting to the plasma membrane and accumulates in the endoplasmic reticulum. The Vangl2^I268N variant no longer physically interacts with its PCP partner DVL3 and has a reduced protein half-life. This mutant provides an important model for dissecting the role of Vangl2 in the development of the neural tube, establishment of polarity of sensory cells of the auditory and vestibular systems, and retinal axon guidance.

Novel mutations in Lrp6 orthologs in mouse and human neural tube defects affect a highly dosage-sensitive Wnt non-canonical planar cell polarity pathway

Wnt signaling has been classified as canonical Wnt/β-catenin-dependent or non-canonical planar cell polarity (PCP) pathway. Misregulation of either pathway is linked mainly to cancer or neural tube defects (NTDs), respectively. Both pathways seem to antagonize each other, and recent studies have implicated a number of molecular switches that activate one pathway while simultaneously inhibiting the other thereby partially mediating this antagonism. The lipoprotein receptor-related protein Lrp6 is crucial for the activation of the Wnt/β-catenin pathway, but its function in Wnt/PCP signaling remains largely unknown. In this study, we investigate the role of Lrp6 as a molecular switch between both Wnt pathways in a novel ENU mouse mutant of Lrp6 (Skax26(m1Jus)) and in human NTDs. We demonstrate that Skax26(m1Jus) represents a hypermorphic allele of Lrp6 with increased Wnt canonical and abolished PCP-induced JNK activities. We also show that Lrp6(Skax26-Jus) genetically interacts with a PCP mutant (Vangl2(Lp)) where double heterozygotes showed an increased frequency of NTDs and defects in cochlear hair cells' polarity. Importantly, our study also demonstrates the association of rare and novel missense mutations in LRP6 that is an inhibitor rather than an activator of the PCP pathway with human NTDs. We show that three LRP6 mutations in NTDs led to a reduced Wnt canonical activity and enhanced PCP signaling. Our data confirm an inhibitory role of Lrp6 in PCP signaling in neurulation and indicate the importance of a tightly regulated and highly dosage-sensitive antagonism between both Wnt pathways in this process.

Role of the planar cell polarity gene CELSR1 in neural tube defects and caudal agenesis

BACKGROUND

Neural tube defects (NTDs), including anencephaly and spina bifida, have a complex etiology. Defects in the planar cell polarity (PCP) signaling pathway have been strongly associated with NTDs in animal models and human cohorts. In this genetic study, we examined the core PCP gene CELSR1 in NTDs and caudal agenesis cases to determine whether mutations at this gene predispose to these defects.

METHODS

We sequenced the coding region and the exon-intron junctions of CELSR1 in a cohort of 473 patients affected with various forms of open and closed NTDs (412) or caudal agenesis (61). Novel and rare variants (<1%) were genotyped in a cohort of 639 ethnically-matched individuals. The effect of novel missense mutations absent in controls and in public databases on protein function was predicted in silico.

RESULTS

We identified in our cohort one nonsense mutation in exon 1 of CELSR1 that truncates the majority of the protein in one patient with NTD and one in-frame 12 bp deletion that removes a putative PKC phosphorylation "SSR" motif in one caudal agenesis patient. We also detected a total of 13 novel missense variants in 12 patients (11 NTDs and 1 caudal agenesis) that were predicted to be pathogenic in silico.

CONCLUSIONS

We detected novel CELSR1 mutations predicted to be pathogenic in 2.9% of our NTD cohort and 3.3% of our caudal agenesis cohort. Our findings implicate CELSR1 as a risk factor for NTDs or caudal agenesis and provide additional evidence for a pathogenic role of PCP signaling in these malformations.

Identification and characterization of novel rare mutations in the planar cell polarity gene PRICKLE1 in human neural tube defects

The planar cell polarity (PCP) pathway controls the process of convergent extension (CE) during gastrulation and neural tube closure, and has been implicated in the pathogenesis of neural tube defects (NTDs) in animal models and human cohorts. In this study, we analyzed the role of one core PCP gene PRICKLE1 in these malformations. We screened this gene in 810 unrelated NTD patients and identified seven rare missense heterozygous mutations that were absent in all controls analyzed and predicted to be functionally deleterious using bioinformatics. Functional validation of five PRICKLE1 variants in a zebrafish model demonstrated that one variant, p.Arg682Cys, antagonized the CE phenotype induced by the wild-type zebrafish prickle1a (zpk1a) in a dominant fashion. Our study demonstrates that PRICKLE1 could act as a predisposing factor to human NTDs and further expands our knowledge of the role of PCP genes in the pathogenesis of these malformations.

Ile481 from the guinea pig alpha-subunit plays a major role in the activation of ENaC by cpt-cAMP

The epithelial sodium channel (ENaC) is the major rate-limiting step for vasopressin and aldosterone sensitive Na(+) reabsorption across kidney epithelia. Recently, ENaC activity was shown to be modulated by extracellular factors such as proteases, Na(+) ion and several other elements. However, the molecular mechanisms of these actions remain unclear. We and others have shown that ENaC composed of the guinea-pig alpha-subunit (alphagp), and the beta gamma rat subunits (betargammar) could be activated by cpt-cAMP, a cAMP analogue, through a mechanism not involving the cAMP-PKA pathway. In the present study, we confirmed by patch-clamp experiments on Xenopus oocytes that the number of open channels increased by 2.4-fold after cpt-cAMP exposure. In order to characterize the extracellular domain involved in this activation, we generated alpha-subunit chimera's harboring different portions of the extracellular loop of the alphagp and alphar. Using two-electrode voltage-clamp, we established that Tyr456-Ser532 from the alphagp confers sensibility to cpt-AMP. Then, by site-directed mutagenesis, we have isolated Ile481 as a major residue for cpt-cAMP-dependant activation. Taken together, these experiments provide evidence of an extracellular-ligand stimulating ENaC. They also contribute to the further understanding of the structure-function relationship of this channel.