Neural Stem Cell Niche Research Articles

Evaluation of Hypothalamic Neural Stem Cell Niche – Implications on Obesity‐Induced Sympathoexcitation

The newly discovered hypothalamic neural stem cell niche is emerging as a key player in the regulation of systemic homeostasis. Previous studies have shown that inflammation‐associated degenerative processes in the hypothalamic neural stem cell niche impairs central regulation of metabolism and contributes to the development of metabolic syndrome in obesity. In addition to energy homeostasis, hypothalamic nuclei specifically paraventricular nucleus, is a well‐known player in the regulation of sympathetic nerve activity and in turn cardiovascular function. How obesity‐induced degeneration of neural stem cell niche affects sympathetic regulation of blood pressure is still not understood. In the present study, we aim to characterize the neural stem cell population from the hypothalamic niche. In this pilot study, 3‐month‐old C57BL/6J mice fed with standard diet were sacrificed and brains were collected for further processing. Hypothalami were freshly isolated and minced. After series of enzymatic dissociation, washing and filtration, NSCs were cultured. On 14th day of culturing, neurospheres were observed without any changes in their structural integrity. Neurosphere counts were recorded, and cells were collected for RNA extraction to perform RT‐PCR analysis for characterization. Our PCR analysis confirmed the expression of NSC markers like nestin, SOX1 and SOX2 suggesting successful isolation and culturing of NSCs in our lab. Earlier studies in our lab, suggest that HFD‐induced obesity causes cellular senescence in the PVN, a region adjacent to the neurogenic niche of hypothalamus. Senescent cells are known to impair the regenerative potential of stem cells by impairment of tissue microenvironment through their secretome. Having established these techniques, future studies will investigate the link between hypothalamic neurogenesis, senescence (in the PVN) and sympathoexcitation in obesity.

Gag-like proteins: Novel mediators of prenatal alcohol exposure in neural development.

BackgroundWe previously showed that ethanol did not kill fetal neural stem cells (NSCs), but that their numbers nevertheless are decreased due to aberrant maturation and loss of self‐renewal. To identify mechanisms that mediate this loss of NSCs, we focused on a family of Gag‐like proteins (GLPs), derived from retroviral gene remnants within mammalian genomes. GLPs are important for fetal development, though their role in brain development is virtually unexplored. Moreover, GLPs may be transferred between cells in extracellular vesicles (EVs) and thereby transfer environmental adaptations between cells. We hypothesized that GLPs may mediate some effects of ethanol in NSCs.MethodsSex‐segregated male and female fetal murine cortical NSCs, cultured ex vivo as nonadherent neurospheres, were exposed to a dose range of ethanol and to mitogen‐withdrawal‐induced differentiation. We used siRNAs to assess the effects of NSC‐expressed GLP knockdown on growth, survival, and maturation and in silico GLP knockout, in an in vivo single‐cell RNA‐sequencing dataset, to identify GLP‐mediated developmental pathways that were also ethanol‐sensitive.ResultsPEG10 isoform‐1, isoform‐2, and PNMA2 were identified as dominant GLP species in both NSCs and their EVs. Ethanol‐exposed NSCs exhibited significantly elevated PEG10 isoform‐2 and PNMA2 protein during differentiation. Both PEG10 and PNMA2 were mediated apoptosis resistance and additionally, PEG10 promoted neuronal and astrocyte lineage maturation. Neither GLP influenced metabolism nor cell cycle in NSCs. Virtual PEG10 and PNMA2 knockout identified gene transcription regulation and ubiquitin‐ligation processes as candidate mediators of GLP‐linked prenatal alcohol effects.ConclusionsCollectively, GLPs present in NSCs and their EVs may confer apoptosis resistance within the NSC niche and contribute to the abnormal maturation induced by ethanol.

Abnormal Development of Neural Stem Cell Niche in the Dentate Gyrus of Menkes Disease.

Background and ObjectivesMenkes disease (MNK) is a rare X-linked recessive disease, caused by mutations in the copper transporting ATP7A gene that is required for copper homeostasis. MNK patients experience various clinical symptoms including neurological defects that are closely related to the prognosis of MNK patients. Neural stem cells (NSCs) in the hippocampal dentate gyrus (DG) produce new neurons throughout life, and defects in DG neurogenesis are often correlated with cognitive and behavioral problems. However, neurodevelopmental defects in the DG during postnatal period in MNK have not been understood yet.Methods and ResultsMottled-brindled (MoBr/y) mice (MNK mice) and littermate controls were used in this study. In vivo microCT imaging and immunohistochemistry results demonstrate that blood vasculatures in hippocampus are abnormally decreased in MNK mice. Furthermore, postnatal establishment of NSC population and their neurogenesis are severely compromised in the DG of MNK mice. In addition, in vitro analyses using hippocampal neurosphere culture followed by immunocytochemistry and immunoblotting suggest that neurogenesis from MNK NSCs is also significantly compromised, corresponding to defective neurogenic gene expression in MNK derived neurons.ConclusionsOur study is the first reports demonstrating that improper expansion of the postnatal NSC population followed by significant reduction of neurogenesis may contribute to neurodevelopmental symptoms in MNK. In conclusion, our results provide new insight into early neurodevelopmental defects in MNK and emphasize the needs for early diagnosis and new therapeutic strategies in the postnatal central nerve system damage of MNK patients.

Bioorthogonally Cross-Linked Hyaluronan-Laminin Hydrogels for 3D Neuronal Cell Culture and Biofabrication.

Laminins (LNs) are key components in the extracellular matrix of neuronal tissues in the developing brain and neural stem cell niches. LN-presenting hydrogels can provide a biologically relevant matrix for the 3D culture of neurons toward development of advanced tissue models and cell-based therapies for the treatment of neurological disorders. Biologically derived hydrogels are rich in fragmented LN and are poorly defined concerning composition, which hampers clinical translation. Engineered hydrogels require elaborate and often cytotoxic chemistries for cross-linking and LN conjugation and provide limited possibilities to tailor the properties of the materials. Here a modular hydrogel system for neural 3D cell cultures, based on hyaluronan and poly(ethylene glycol), that is cross-linked and functionalized with human recombinant LN-521 using bioorthogonal copper-free click chemistry, is shown. Encapsulated human neuroblastoma cells demonstrate high viability and grow into spheroids. Long-term neuroepithelial stem cells (lt-NES) cultured in the hydrogels can undergo spontaneous differentiation to neural fate and demonstrate significantly higher viability than cells cultured without LN. The hydrogels further support the structural integrity of 3D bioprinted structures and maintain high viability of bioprinted and syringe extruded lt-NES, which can facilitate biofabrication and development of cell-based therapies.

Developmental thyroid disruption permanently affects the neuroglial output in the murine subventricular zone.

SummaryNeural stem cells (NSCs) in the adult brain are a source of neural cells for brain injury repair. We investigated whether their capacity to generate new neurons and glia is determined by thyroid hormone (TH) during development because serum levels peak during postnatal reorganization of the main NSC niche, the subventricular zone (SVZ). Re-analysis of mouse transcriptome data revealed increased expression of TH transporters and deiodinases in postnatal SVZ NSCs, promoting local TH action, concomitant with a burst in neurogenesis. Inducing developmental hypothyroidism reduced NSC proliferation, disrupted expression of genes implicated in NSC determination and TH signaling, and altered the neuron/glia output in newborns. Three-month-old adult mice recovering from developmental hypothyroidism had fewer olfactory interneurons and underperformed on short-memory odor tests, dependent on SVZ neurogenesis. Our data provide readouts permitting comparison with adverse long-term events following thyroid disruptor exposure and ideas regarding the etiology of prevalent neurodegenerative diseases in industrialized countries.

4D imaging analysis of the aging mouse neural stem cell niche reveals a dramatic loss of progenitor cell dynamism regulated by the RHO-ROCK pathway.

SummaryIn the adult ventricular-subventricular zone (V-SVZ), neural stem cells (NSCs) give rise to transit-amplifying progenitor (TAP) cells. These progenitors reside in different subniche locations, implying that cell movement must accompany lineage progression, but the dynamic behaviors of adult NSCs and TAPs remain largely unexplored. Here, we performed live time-lapse imaging with computer-based image analysis of young and aged 3D V-SVZ wholemounts from transgenic mice with fluorescently distinguished NSCs and TAP cells. Young V-SVZ progenitors are highly dynamic, with regular process outgrowth and retraction and cell migration. However, these activities dramatically declined with age. An examination of single-cell RNA sequencing (RNA-seq) data revealed age-associated changes in the Rho-Rock pathway that are important for cell motility. Applying a small molecule to inhibit ROCK transformed young into old V-SVZ progenitor cell dynamic behaviors. Hence RHO-ROCK signaling is critical for normal adult NSC and TAP movement and interactions, which are compromised with age, concomitant with the loss of regenerative ability.

Heterogeneity of quiescent and active neural stem cells in the postnatal brain.

In the postnatal mammalian brain, neurogenic activity is retained in anatomically restricted areas, driven by pools of Neural Stem Cells (NSCs). These cells and their progeny have been studied intensively as potential targets for regenerative treatments, aiming at either their in situ manipulation or their use as sources of cells for transplantation-based strategies. Although their full identity, heterogeneity and differentiation potential remain elusive, due to the absence of specific cell-type markers, our knowledge of their properties is constantly expanding. Here, we focus on the NSC niche that is located at the Subependymal Zone (SEZ/ also known as Subventricular Zone) of the lateral ventricles of the brain. We review, summarize and explain the different faces of the NSC, as they have been described, using a wide range of experimental approaches, over a time-frame of three decades: the primitive, definitive, quiescent or activated NSC. We also review the growing evidence of the existence of latent NSCs outside of niches, in the brain parenchyma, that constitute promising new therapeutic targets, complemented by the novel technologies of in vivo cell reprogramming.

ADAM10 facilitates rapid neural stem cell cycling and proper positioning within the subventricular zone niche via JAMC/RAP1Gap signaling.

The mechanisms that regulate neural stem cell (NSC) lineage progression and maintain NSCs within different domains of the adult neural stem cell niche, the subventricular zone are not well defined. Quiescent NSCs are arranged at the apical ventricular wall, while mitotically activated NSCs are found in the basal, vascular region of the subventricular zone. Here, we found that ADAM10 (a disintegrin and metalloproteinase 10) is essential in NSC association with the ventricular wall, and via this adhesion to the apical domain, ADAM10 regulates the switch from quiescent and undifferentiated NSC to an actively proliferative and differentiating cell state. Processing of JAMC (junctional adhesion molecule C) by ADAM10 increases Rap1GAP activity. This molecular machinery promotes NSC transit from the apical to the basal compartment and subsequent lineage progression. Understanding the molecular mechanisms responsible for regulating the proper positioning of NSCs within the subventricular zone niche and lineage progression of NSCs could provide new targets for drug development to enhance the regenerative properties of neural tissue.

Estimation of the density of neural, glial, and endothelial lineage cells in the adult mouse dentate gyrus.

The dentate gyrus subregion of the mammalian hippocampus is an adult neural stem cell niche and site of lifelong neurogenesis. Hypotheses regarding the role of adult-born neuron synaptic integration in hippocampal circuit function are framed by robust estimations of adult-born versus pre/perinatally-born neuron number. In contrast, the non-neurogenic functions of adult neural stem cells and their immediate progeny, such as secretion of bioactive growth factors and expression of extracellular matrix-modifying proteins, lack similar framing due to few estimates of their number versus other prominent secretory cells. Here, we apply immunohistochemical methods to estimate cell density of neural stem/progenitor cells versus other major classes of glial and endothelial cell types that are potentially secretory in the dentate gyrus of adult mice. Of the cell types quantified, we found that GFAP+SOX2+ stellate astrocytes were the most numerous, followed by CD31+ endothelia, GFAP-SOX2+ intermediate progenitors, Olig2+ oligodendrocytes, Iba1+ microglia, and GFAP+SOX2+ radial glia-like neural stem cells. We did not observe any significant sex differences in density of any cell population. Notably, neural stem/progenitor cells were present at a similar density as several cell types known to have potent functional roles via their secretome. These findings may be useful for refining hypotheses regarding the contributions of these cell types to regulating hippocampal function and their potential therapeutic uses. All experimental protocols were approved by the Ohio State University Institutional Animal Care and Use Committee (protocol# 2016A00000068) on July 14, 2016.

Biomaterials patterning regulates neural stem cells fate and behavior: The interface of biology and material science.

The combination of nanotechnology and stem cell biology is one of the most promising advances in the field of regenerative medicine. This novel combination has widely been utilized in vitro settings in an attempt to develop efficient therapeutic strategies to overcome the limited capacity of the central nervous system (CNS) in replacing degenerating neural cells with functionally normal cells after the onset of acute and chronic neurological disorders. Importantly, biomaterials, not only, enhance the endogenous CNS neurogenesis and plasticity, but also, could provide a desirable supportive microenvironment to harness the full potential of the in vitro expanded neural stem cells (NSCs) for regenerative purposes. Here, first, we discuss how the physical and biochemical properties of biomaterials, such as their stiffness and elasticity, could influence the behavior of NSCs. Then, since the NSCs niche or microenvironment is of fundamental importance in controlling the dynamic destiny of NSCs such as their quiescent and proliferative states, topographical effects of surface diversity in biomaterials, that is, the micro-and nano-patterned surfaces will be discussed in detail. Finally, the influence of biomaterials as artificial microenvironments on the behavior of NSCs through the specific mechanotransduction signaling pathway mediated by focal adhesion formation will be reviewed.

3D Reconstitution of the Neural Stem Cell Niche: Connecting the Dots.

Neural stem cells (NSCs) are important constituents of the nervous system, and they become constrained in two specific regions during adulthood: the subventricular zone (SVZ) and the subgranular zone (SGZ) of the dentate gyrus in the hippocampus. The SVZ niche is a limited-space zone where NSCs are situated and comprised of growth factors and extracellular matrix (ECM) components that shape the microenvironment of the niche. The interaction between ECM components and NSCs regulates the equilibrium between self-renewal and differentiation. To comprehend the niche physiology and how it controls NSC behavior, it is fundamental to develop in vitro models that resemble adequately the physiologic conditions present in the neural stem cell niche. These models can be developed from a variety of biomaterials, along with different biofabrication approaches that permit the organization of neural cells into tissue-like structures. This review intends to update the most recent information regarding the SVZ niche physiology and the diverse biofabrication approaches that have been used to develop suitable microenvironments ex vivo that mimic the NSC niche physiology.

Galectins and Their Ligand Glycoconjugates in the Central Nervous System Under Physiological and Pathological Conditions.

Galectins are β-galactoside-binding lectins consisting of 15 members in mammals. Galectin-1,-3,-4,-8, and -9 are predominantly expressed in the central nervous system (CNS) and regulate various physiological and pathological events. This review summarizes the current knowledge of the cellular expression and role of galectins in the CNS, and discusses their functions in neurite outgrowth, myelination, and neural stem/progenitor cell niches, as well as in ischemic/hypoxic/traumatic injuries and neurodegenerative diseases such as multiple sclerosis. Galectins are expressed in both neurons and glial cells. Galectin-1 is mainly expressed in motoneurons, whereas galectin-3-positive neurons are broadly distributed throughout the brain, especially in the hypothalamus, indicating its function in the regulation of homeostasis, stress response, and the endocrine/autonomic system. Astrocytes predominantly contain galectin-1, and galectin-3 and−9 are upregulated along with its activation. Activated, but not resting, microglia contain galectin-3, supporting its phagocytic activity. Galectin-1,−3, and -4 are characteristically expressed during oligodendrocyte differentiation. Galectin-3 from microglia promotes oligodendrocyte differentiation and myelination, while galectin-1 and axonal galectin-4 suppress its differentiation and myelination. Galectin-1- and- 3-positive cells are involved in neural stem cell niche formation in the subventricular zone and hippocampal dentate gyrus, and the migration of newly generated neurons and glial cells to the olfactory bulb or damaged lesions. In neurodegenerative diseases, galectin-1,-8, and -9 have neuroprotective and anti-inflammatory activities. Galectin-3 facilitates pro-inflammatory action; however, it also plays an important role during the recovery period. Several ligand glycoconjugates have been identified so far such as laminin, integrins, neural cell adhesion molecule L1, sulfatide, neuropilin-1/plexinA4 receptor complex, triggering receptor on myeloid cells 2, and T cell immunoglobulin and mucin domain. N-glycan branching on lymphocytes and oligodendroglial progenitors mediated by β1,6-N-acetylglucosaminyltransferase V (Mgat5/GnTV) influences galectin-binding, modulating inflammatory responses and remyelination in neurodegenerative diseases. De-sulfated galactosaminoglycans such as keratan sulfate are potential ligands for galectins, especially galectin-3, regulating neural regeneration. Galectins have multitudinous functions depending on cell type and context as well as post-translational modifications, including oxidization, phosphorylation, S-nitrosylation, and cleavage, but there should be certain rules in the expression patterns of galectins and their ligand glycoconjugates, possibly related to glucose metabolism in cells.

NSCs Under Strain—Unraveling the Mechanoprotective Role of Differentiating Astrocytes in a Cyclically Stretched Coculture With Differentiating Neurons

The neural stem cell (NSC) niche is a highly vascularized microenvironment that supplies stem cells with relevant biological and chemical cues. However, the NSCs’ proximity to the vasculature also means that the NSCs are subjected to permanent tissue deformation effected by the vessels’ heartbeat-induced pulsatile movements. Cultivating NSCs under common culture conditions neglects the—yet unknown—influence of this cyclic mechanical strain on neural stem cells. Under the hypothesis that pulsatile strain should affect essential NSC functions, a cyclic uniaxial strain was applied under biomimetic conditions using an in-house developed stretching system based on cross-linked polydimethylsiloxane (PDMS) elastomer. While lineage commitment remained unaffected by cyclic deformation, strain affected NSC quiescence and cytoskeletal organization. Unexpectedly, cyclically stretched stem cells aligned in stretch direction, a phenomenon unknown for other types of cells in the mammalian organism. The same effect was observed for young astrocytes differentiating from NSCs. In contrast, young neurons differentiating from NSCs did not show mechanoresponsiveness. The exceptional orientation of NSCs and young astrocytes in the stretch direction was blocked upon RhoA activation and went along with a lack of stress fibers. Compared to postnatal astrocytes and mature neurons, NSCs and their young progeny displayed characteristic and distinct mechanoresponsiveness. Data suggest a protective role of young astrocytes in mixed cultures of differentiating neurons and astrocytes by mitigating the mechanical stress of pulsatile strain on developing neurons.

Isolation and Culture of Neural Stem/Progenitor Cells from the Postnatal Periventricular Region.

Due to the complexity of the neural stem cell (NSC) niche organization, the lack of specific NSC markers, and the difficulty of long-term tracking these cells and their progeny in vivo, the functional properties of the endogenous NSCs remain largely unexplored. These limitations have led to the development of methodologies to efficiently isolate, expand, and differentiate NSCs ex vivo. We describe here the peculiarities of the neurosphere assay (NSA) as a methodology that allows to efficiently isolate, expand, and differentiate somatic NSCs derived from the postnatal and adult forebrain periventricular region while preserving proliferation, self-renewal, and multipotency, the main attributes that provide their functional identification.

Neonatal Transplant in Hypoxic Injury.

Even with therapeutic hypothermia as standard of care, hypoxic-ischemic encephalopathy in neonates often causes long-term disabilities. Stem cell therapy may be a successful treatment for HIE both in the acute and chronic time periods post-injury. Neurogenic astrocytes with characteristics of neural stem cells can be cultured as adherent monolayers and be induced to generate neuronal progeny in vitro and in vivo following reintroduction into the neural stem cell niche of both neonatal and adult hosts. Thus, these neurogenic astrocytes represent promising candidates for cell replacement therapy in HIE. Such an approach requires optimized cell cultivation protocols as well as extensive testing of donor cells to assess their capacity for engraftment, survival, and integration in the HIE animal models. In this chapter, we will describe methods of generating the HIE model, generating and culturing monolayer neurogenic astrocytes, and transplanting these cells into HIE animal models.

Roles of Enteric Neural Stem Cell Niche and Enteric Nervous System Development in Hirschsprung Disease.

The development of the enteric nervous system (ENS) is highly modulated by the synchronized interaction between the enteric neural crest cells (ENCCs) and the neural stem cell niche comprising the gut microenvironment. Genetic defects dysregulating the cellular behaviour(s) of the ENCCs result in incomplete innervation and hence ENS dysfunction. Hirschsprung disease (HSCR) is a rare complex neurocristopathy in which the enteric neural crest-derived cells fail to colonize the distal colon. In addition to ENS defects, increasing evidence suggests that HSCR patients may have intrinsic defects in the niche impairing the extracellular matrix (ECM)-cell interaction and/or dysregulating the cellular niche factors necessary for controlling stem cell behaviour. The niche defects in patients may compromise the regenerative capacity of the stem cell-based therapy and advocate for drug- and niche-based therapies as complementary therapeutic strategies to alleviate/enhance niche-cell interaction. Here, we provide a summary of the current understandings of the role of the enteric neural stem cell niche in modulating the development of the ENS and in the pathogenesis of HSCR. Deciphering the contribution of the niche to HSCR may provide important implications to the development of regenerative medicine for HSCR.

A Shift in Tissue Stiffness During Hippocampal Maturation Correlates to the Pattern of Neurogenesis and Composition of the Extracellular Matrix.

Aging changes the mechanical properties of brain tissue, such as stiffness. It has been proposed that the maintenance and differentiation of neural stem cells (NSCs) are regulated in accordance with extracellular stiffness. Neurogenesis is observed in restricted niches, including the dentate gyrus (DG) of the hippocampus, throughout mammalian lifetimes. However, profiles of tissue stiffness in the DG in comparison with the activity of NSCs from the neonatal to the matured brain have rarely been addressed so far. Here, we first applied ultrasound-based shear-wave elasticity imaging (SWEI) in living animals to assess shear modulus as in vivo brain stiffness. To complement the assay, atomic force microscopy (AFM) was utilized to determine the Young’s modulus in the hippocampus as region-specific stiffness in the brain slice. The results revealed that stiffness in the granule cell layer (GCL) and the hilus, including the subgranular zone (SGZ), increased during hippocampal maturation. We then quantified NSCs and immature neural cells in the DG with differentiation markers, and verified an overall decrease of NSCs and proliferative/immature neural cells along stages, showing that a specific profile is dependent on the subregion. Subsequently, we evaluated the amount of chondroitin sulfate proteoglycans (CSPGs), the major extracellular matrix (ECM) components in the premature brain by CS-56 immunoreactivity. We observed differential signal levels of CSPGs by hippocampal subregions, which became weaker during maturation. To address the contribution of the ECM in determining tissue stiffness, we manipulated the function of CSPGs by enzymatic digestion or supplementation with chondroitin sulfate, which resulted in an increase or decrease of stiffness in the DG, respectively. Our results illustrate that stiffness in the hippocampus shifts due to the composition of ECM, which may affect postnatal neurogenesis by altering the mechanical environment of the NSC niche.

Histological Studies of the Ventricular–Subventricular Zone as Neural Stem Cell and Glioma Stem Cell Niche

The neural stem cell niche of the ventricular-subventricular zone supports the persistence of stem and progenitor cells in the mature brain. This niche has many notable cytoarchitectural features that affect the activity of stem cells and may also support the survival and growth of invading tumor cells. Histochemical studies of the niche have revealed many proteins that, in combination, can help to reveal stem-like cells in the normal or cancer context, although many caveats persist in the quest to consistently identify these cells in the human brain. Here, we explore the complex relationship between the persistent proliferative capacity of the neural stem cell niche and the malignant proliferation of brain tumors, with a special focus on histochemical identification of stem cells and stem-like tumor cells and an eye toward the potential application of high-dimensional imaging approaches to the field.

Regulation of the Brain Neural Niche by Soluble Molecule Akhirin.

In the central nervous system (CNS), which comprises the eyes, spinal cord, and brain, neural cells are produced by the repeated division of neural stem cells (NSCs) during the development of the CNS. Contrary to the notion that the CNS is relatively static with a limited cell turnover, cells with stem cell-like properties have been isolated from most neural tissues. The microenvironment, also known as the NSC niche, consists of NSCs/neural progenitor cells, other neurons, glial cells, and blood vessels; this niche is thought to regulate neurogenesis and the differentiation of NSCs into neurons and glia. Although it has been established that neurons, glia, and blood vessels interact with each other in a complex manner to generate neural tissues in the NSC niche, the underlying molecular mechanisms in the CNS niche are unclear. Herein, we would like to introduce the extracellular secreted protein, Akhirin (AKH; Akhi is the Bengali translation for eye). AKH is specifically expressed in the CNS niche—the ciliary body epithelium in the retina, the central canal of the spinal cord, the subventricular zone, and the subgranular zone of the dentate gyrus of the hippocampus—and is supposedly involved in NSC niche regulation. In this review, we discuss the role of AKH as a niche molecule during mouse brain formation.

Microtubule disruption upon CNS damage triggers mitotic entry via TNF signaling activation.

Repair after traumatic injury often starts with mitotic activation around the lesion edges. Early midline cells in the Drosophila embryonic CNS can enter into division following the traumatic disruption of microtubules. We demonstrate that microtubule disruption activates non-canonical TNF signaling by phosphorylation of TGF-β activated kinase 1 (Tak1) and its target IkappaB kinase (Ik2), culminating in Dorsal/NfkappaB nuclear translocation and Jra/Jun expression. Tak1 and Ik2 are necessary for the damaged-induced divisions. Microtubule disruption caused by Tau accumulation is also reported in Alzheimer's disease (AD). Human Tau expression in Drosophila midline cells is sufficient to induce Tak1 phosphorylation, Dorsal and Jra/Jun expression, and entry into mitosis. Interestingly, activation of Tak1 and Tank binding kinase 1 (Tbk1), the human Ik2 ortholog, and NfkappaB upregulation are observed in AD brains.