Disabled 1 Is Part of a Signaling Pathway Activated by Epidermal Growth Factor Receptor

Dab1 expression level controls Reelin-induced PI3K-Akt activation in early GABAergic neurons

Disabled-1 (Dab1) is a key regulator of the Reelin signaling cascades and controls many neurodevelopmental processes, including pyramidal neuron migration, dendrite growth, and spine formation. Dab1 is phosphorylated upon the binding of Reelin to Very low density lipoprotein receptor (VLDLR) and Apolipoprotein E receptor 2 (ApoER2) receptors, resulting in activation of a series of downstream signaling pathways, including Phosphoinositide 3-kinase (PI3K)/Akt, Lissencephaly 1 (Lis1), Crks/C3G, and Extracellular signal-regulated kinase 1/2 (Erk1/2). Dab1 is then rapidly degraded via the proteasome pathway. In humans, REELIN and DAB1 are genetically associated with several psychiatric disorders, such as schizophrenia and autism spectrum disorder. Although a subset of GABAergic neurons express Reelin and are continuously exposed to Reelin from early developmental stages through adulthood, most studies have only investigated the role of Reelin in the development and function of pyramidal neurons; as such the role of Reelin in GABAergic neurons remains poorly understood. In this study, we isolated primary neurons from mouse medial ganglionic eminence (MGE) at embryonic day 14.5 that 98-99 % were composed of GABAergic neurons. Using MGE-isolated GABAergic neurons, we studied the quantitative differences in Reelin signaling and expression of related genes in these neurons for the first time. Reelin supplementation did not activate PI3K-Akt signaling in most GABAergic neurons, but it did activate the signaling pathway in Somatostatin-positive GABAergic neurons. Dab1 was transcriptionally repressed in early GABAergic neurons, demonstrating the selective activation of Reelin signaling between subsets of neurons. This study provides quantitative evidence and contributes insights into the molecular mechanisms underlying the limited effects of Reelin on Dab1-related developmental activities in the majority of GABAergic neurons during brain development.

Autophagy markers expression pattern in developing liver of the yotari (dab1-/-) mice and humans

Autophagy plays an important role in the physiology and pathology of the liver. Several negative autophagy regulators have been discovered, including epidermal growth factor receptor (EGFR), mediated by activation of the PI3K/Akt/mTOR signaling pathway. Disabled-1 (Dab1) is one of the mediating adaptor factors of PI3K/Akt/mTOR signaling pathways. We investigated the potential impact of Dab1 on autophagy-related markers (LC3B, LAMP2A, HSC70, and GRP78) in the developing liver by using a model of yotari mice and compared it with autophagy marker expression in human liver development. Mouse embryos were obtained at gestation days 13.5 and 15.5 (E13.5 and E15.5), and a total of 5 normal human conceptuses were obtained between gestation days 5 and 10. Histological sections were analyzed by immunohistochemistry. The highest expression of the early endosome-forming factor LC3B and the microautophagy factor LAMP2a was observed at the transition from embryonic to early fetal phase, whereas the expression of the chaperones HSC 70 and GRP78 was highest at embryonic phase. The expression patterns of three of these factors in mouse liver were different from those in human liver: the expression of LC3B was high at E13.5, that of HSC 70 at 15.5, whereas the expression of GRP78 did not change significantly. On the other hand, the expression pattern of LAMP2a was similar to that in human development and was higher at E15.5 than at E13.5. Moreover, knockout of Dab1 resulted in significantly lower expression of LC3B and LAMP2a in mouse embryo livers (at E13.5), indicating a possible role of Dab1 in regulating autophagy during embryonic development in the liver.

Excitatory neurons and oligodendrocyte precursor cells are vulnerable to focal cortical dysplasia type IIIa as suggested by single-nucleus multiomics

BACKGROUND

Focal cortical dysplasia (FCD) is a heterogeneous group of cortical developmental malformations that constitute a common cause of medically intractable epilepsy. FCD type IIIa (FCD IIIa) refers to temporal neocortex alterations in architectural organisation or cytoarchitectural composition in the immediate vicinity of hippocampal sclerosis. Slight alterations in the temporal neocortex of FCD IIIa patients pose a challenge for the preoperative diagnosis and definition of the resection range.

METHODS

We have performed multimodal integration of single-nucleus RNA sequencing and single-nucleus assay for transposase-accessible chromatin sequencing in the epileptogenic cortex of four patients with FCD IIIa, and three relatively normal temporal neocortex were chosen as controls.

RESULTS

Our study revealed that the most significant dysregulation occurred in excitatory neurons (ENs) and oligodendrocyte precursor cells (OPCs) in the epileptogenic cortex of FCD IIIa patients. In ENs, we constructed a transcription factor (TF)-hub gene regulatory network and found DAB1high ENs subpopulation mediates neuronal immunity characteristically in FCD IIIa. Western blotting and immunofluorescence were used to validate the changes in protein expression levels caused by some of the key genes. The OPCs were activated and exhibited aberrant phenotypes in FCD IIIa, and TFs regulating reconstructed pseudotime trajectory were identified. Finally, our results revealed aberrant intercellular communication between ENs and OPCs in FCD IIIa patients.

CONCLUSIONS

Our study revealed significant and intricate alterations in the transcriptomes and epigenomes in ENs and OPCs of FCD IIIa patients, shedding light on their cell type-specific regulation and potential pathogenic involvement in this disorder. This work will help evaluate the pathogenesis of cortical dysplasia and epilepsy and explore potential therapeutic targets.

KEY POINTS

Paired snRNA-seq and snATAC-seq data were intergrated and analysed to identify crucial subpopulations of ENs and OPCs in the epileptogenic cortex of FCD IIIa patients and explore their possible pathogenic role in the disease. A TF-hub gene regulatory network was constructed in ENs, and the DAB1high Ex-1 mediated neuronal immunity was characterstically in FCD IIIa patients. The OPCs were activated and exhibited aberrant phenotypes in FCD IIIa patients, and TFs regulating reconstructed pseudotime traectory were identified. Aberrant intercelluar communications between ENs and OPCs in FCD IIIa patients were identified.

EphA4 Induces the Phosphorylation of an Intracellular Adaptor Protein Dab1 via Src Family Kinases

Dab1 is an intracellular adaptor protein essential for brain formation during development. Tyrosine phosphorylation in Dab1 plays important roles in neuronal migration, dendrite development, and synapse formation by affecting several downstream pathways. Reelin is the best-known extracellular protein that induces Dab1 phosphorylation. However, whether other upstream molecule(s) contribute to Dab1 phosphorylation remains largely unknown. Here, we found that EphA4, a member of the Eph family of receptor-type tyrosine kinases, induced Dab1 phosphorylation when co-expressed in cultured cells. Tyrosine residues phosphorylated by EphA4 were the same as those phosphorylated by Reelin in neurons. The autophosphorylation of EphA4 was necessary for Dab1 phosphorylation. We also found that EphA4-induced Dab1 phosphorylation was mediated by the activation of the Src family tyrosine kinases. Interestingly, Dab1 phosphorylation was not observed when EphA4 was activated by ephrin-A5 in cultured cortical neurons, suggesting that Dab1 is localized in a different compartment in them. EphA4-induced Dab1 phosphorylation may occur under limited and/or pathological conditions in the brain.

Disturbances in Switching between Canonical and Non-Canonical Wnt Signaling Characterize Developing and Postnatal Kidneys of Dab1-/- (yotari) Mice

This study aims to determine the protein expression patterns of acetylated α-tubulin, inversin, dishevelled-1, Wnt5a/b, and β-catenin in developing (E13.5 and E15.5) and early postnatal (P4 and P14) kidneys of Dab1^-/- (yotari) mice, their role in regulating the Wnt signaling pathway, and the possible relation to congenital anomalies of kidney and urinary tract (CAKUT). The analysis of target protein co-expression, observed in the renal vesicles/immature glomeruli, ampullae/collecting ducts, convoluted tubules, metanephric mesenchyme of developing kidneys, but proximal convoluted tubules, distal convoluted tubules and glomeruli of postnatal kidneys, was performed using double immunofluorescence and semi-quantitative methods. The overall expression of acetylated α-tubulin and inversin during normal kidney development increases with higher expression in yotari mice as the kidney acquires mature morphology. An increase in β-catenin and cytosolic DVL-1 levels, indicating a switch from non-canonical to canonical Wnt signaling, is found in the postnatal kidney of yotari mice. In contrast, healthy mouse kidney expresses inversin and Wnt5a/b in the postnatal period, thus activating non-canonical Wnt signaling. Target protein expression patterns in kidney development and the early postnatal period observed in this study could indicate that switching between canonical and non-canonical Wnt signaling is crucial for normal nephrogenesis, while the defective Dab1 gene product in yotari mice may promote CAKUT due to interfering with this process.

Evidence of Reelin Signaling in GBM and Its Derived Cancer Stem Cells

Glioblastoma (GBM) is the most aggressive and malignant form of primary brain cancer, characterized by an overall survival time ranging from 12 to 18 months. Despite the progress in the clinical treatment and the growing number of experimental data aimed at investigating the molecular bases of GBM development, the disease remains characterized by a poor prognosis. Recent studies have proposed the existence of a population of GBM cancer stem cells (CSCs) endowed with self-renewal capability and a high tumorigenic potential that are believed to be responsible for the resistance against common chemotherapy and radiotherapy treatments. Reelin is a large secreted extracellular matrix glycoprotein, which contributes to positioning, migration, and laminar organization of several central nervous system structures during brain development. Mutations of the reelin gene have been linked to disorganization of brain structures during development and behavioral anomalies. In this study, we explored the expression of reelin in GBM and its related peritumoral tissue and performed the same analysis in CSCs isolated from both GBM (GCSCs) and peritumoral tissue (PCSCs) of human patients. Our findings reveal (i) the higher expression of reelin in GBM compared to the peritumoral tissue by immunohistochemical analysis, (ii) the mRNA expression of both reelin and its adaptor molecule Dab1 in either CSC subtypes, although at a different extent; and (iii) the contribution of CSCs-derived reelin in the migration of human primary GBM cell line U87MG. Taken together, our data indicate that the expression of reelin in GBM may represent a potential contribution to the regulation of GBM cancer stem cells behavior, further stimulating the interest on the reelin pathway as a potential target for GBM treatment.