Glia In Cortex Research Articles

Conserved miR-8/miR-200 Defines a Glial Niche that Controls Neuroepithelial Expansion and Neuroblast Transition

Neuroepithelial cell proliferation must be carefully balanced with the transition to neuroblast (neural stem cell) to control neurogenesis. Here, we show that loss of the Drosophila microRNA mir-8 (the homolog of vertebrate miR-200 family) results in both excess proliferation and ectopic neuroblast transition. Unexpectedly, mir-8 is expressed in a subpopulation of optic-lobe-associated cortex glia that extend processes that ensheath the neuroepithelium, suggesting that glia cells communicate with the neuroepithelium. We provide evidence that miR-8-positive glia express Spitz, a transforming growth factor α (TGF-α)-like ligand that triggers epidermal growth factor receptor (EGFR) activation to promote neuroepithelial proliferation and neuroblast formation. Further, our experiments suggest that miR-8 ensures both a correct glial architecture and the spatiotemporal control of Spitz protein synthesis via direct binding to Spitz 3' UTR. Together, these results establish glial-derived cues as key regulatory elements in the control of neuroepithelial cell proliferation and the neuroblast transition.

Gliogenesis in the embryonic brain of the grasshopper Schistocerca gregaria with particular focus on the protocerebrum prior to mid-embryogenesis

I investigate the pattern of gliogenesis in the brain of the grasshopper Schistocerca gregaria prior to mid-embryogenesis, with particular focus on the protocerebrum. Using the glia-specific marker Repo and the neuron-specific marker HRP, I identify three types of glia with respect to their respective positions in the brain: surface glia form the outmost cell layer ensheathing the brain; cortex glia are intermingled with neuronal somata forming the brain cortex; and neuropil glia are associated with brain neuropils. The ontogeny of each glial type has also been studied. At 24% of embryogenesis, a few glia are observed in each hemisphere of the proto-, deuto- and tritocerebrum. In each protocerebral hemisphere, such glia form a cluster that expands rapidly during later development. Closer examination reveals proliferative glia in such clusters at ages spanning from 24 to 36% of embryogenesis, indicating that glial proliferation may account for the expansion of the clusters. Data derived from 33-39% of embryogenesis suggest that, in the protocerebrum, each type of glia is likely to be generated by its respective progenitor-forming clusters. Moreover, the glial cluster located at the anterior end of the brain can give rise to both surface glia and cortex glia that populate the protocerebrum via subsequent migration. Proliferation is observed for all three glial types, indicating a possible source for the glia.

A multipotent transit-amplifying neuroblast lineage in the central brain gives rise to optic lobe glial cells in Drosophila

The neurons and glial cells of the Drosophila brain are generated by neural stem cell-like progenitors during two developmental phases, one short embryonic phase and one more prolonged postembryonic phase. Like the bulk of the adult-specific neurons, most of glial cells found in the adult central brain are generated postembryonically. Five of the neural stem cell-like progenitors that give rise to glial cells during postembryonic brain development have been identified as type II neuroglioblasts that generate neural and glial progeny through transient amplifying INPs. Here we identify DL1 as a novel multipotent neuroglial progenitor in the central brain and show that this type II neuroblast not only gives rise to neurons that innervate the central complex but also to glial cells that contribute exclusively to the optic lobe. Immediately following their generation in the central brain during the second half of larval development, these DL1 lineage-derived glia migrate into the developing optic lobe, where they differentiate into three identified types of optic lobe glial cells, inner chiasm glia, outer chiasm glia and cortex glia. Taken together, these findings reveal an unexpected central brain origin of optic lobe glial cells and central complex interneurons from one and the same type II neuroglioblast.

Mutation of a NCKX Eliminates Glial Microdomain Calcium Oscillations and Enhances Seizure Susceptibility

Glia exhibit spontaneous and activity-dependent fluctuations in intracellular Ca(2+), yet it is unclear whether glial Ca(2+) oscillations are required during neuronal signaling. Somatic glial Ca(2+) waves are primarily mediated by the release of intracellular Ca(2+) stores, and their relative importance in normal brain physiology has been disputed. Recently, near-membrane microdomain Ca(2+) transients were identified in fine astrocytic processes and found to arise via an intracellular store-independent process. Here, we describe the identification of rapid, near-membrane Ca(2+) oscillations in Drosophila cortex glia of the CNS. In a screen for temperature-sensitive conditional seizure mutants, we identified a glial-specific Na(+)/Ca(2+), K(+) exchanger (zydeco) that is required for microdomain Ca(2+) oscillatory activity. We found that zydeco mutant animals exhibit increased susceptibility to seizures in response to a variety of environmental stimuli, and that zydeco is required acutely in cortex glia to regulate seizure susceptibility. We also found that glial expression of calmodulin is required for stress-induced seizures in zydeco mutants, suggesting a Ca(2+)/calmodulin-dependent glial signaling pathway underlies glial-neuronal communication. These studies demonstrate that microdomain glial Ca(2+) oscillations require NCKX-mediated plasma membrane Ca(2+) flux, and that acute dysregulation of glial Ca(2+) signaling triggers seizures.

Neuropathological changes in the nucleus basalis in schizophrenia

The nucleus basalis has not been examined in detail in severe mental illness. Several studies have demonstrated decreases in glia and glial markers in the cerebral cortex in schizophrenia, familial bipolar disorder and recurrent depression. Changes in neocortical neuron size and shape have also been reported. The nucleus basalis is a collection of large cholinergic neurons in the basal forebrain receiving information from the midbrain and limbic system, projecting to the cortex and involved with attention, learning and memory, and receives regulation from serotonergic inputs. Forty-one cases aged 41-60 years with schizophrenia or major depressive disorder with age-matched controls were collected. Formalin-fixed paraffin-embedded coronal nucleus basalis sections were histologically stained for oligodendrocyte identification with cresyl-haematoxylin counterstain, for neuroarchitecture with differentiated cresyl violet stain and astrocytes were detected by glial fibrillary acid protein immunohistochemistry. Cell density and neuroarchitecture were measured using Image Pro Plus. There were larger NB oval neuron soma in the combined schizophrenia and major depression disorder groups (p = 0.038), with no significant change between controls and schizophrenia and major depression disorder separately. There is a significant reduction in oligodendrocyte density (p = 0.038) in the nucleus basalis in schizophrenia. The ratio of gemistocytic to fibrillary astrocytes showed a greater proportion of the former in schizophrenia (18.1 %) and major depressive disorder (39.9 %) than in controls (7.9 %). These results suggest glial cell abnormalities in the nucleus basalis in schizophrenia possibly leading to cortical-limbic disturbance and subcortical dysfunction.

Concerted control of gliogenesis by InR/TOR and FGF signalling in the Drosophila post-embryonic brain.

Glial cells are essential for the development and function of the nervous system. In the mammalian brain, vast numbers of glia of several different functional types are generated during late embryonic and early foetal development. However, the molecular cues that instruct gliogenesis and determine glial cell type are poorly understood. During post-embryonic development, the number of glia in the Drosophila larval brain increases dramatically, potentially providing a powerful model for understanding gliogenesis. Using glial-specific clonal analysis we find that perineural glia and cortex glia proliferate extensively through symmetric cell division in the post-embryonic brain. Using pan-glial inhibition and loss-of-function clonal analysis we find that Insulin-like receptor (InR)/Target of rapamycin (TOR) signalling is required for the proliferation of perineural glia. Fibroblast growth factor (FGF) signalling is also required for perineural glia proliferation and acts synergistically with the InR/TOR pathway. Cortex glia require InR in part, but not downstream components of the TOR pathway, for proliferation. Moreover, cortex glia absolutely require FGF signalling, such that inhibition of the FGF pathway almost completely blocks the generation of cortex glia. Neuronal expression of the FGF receptor ligand Pyramus is also required for the generation of cortex glia, suggesting a mechanism whereby neuronal FGF expression coordinates neurogenesis and cortex gliogenesis. In summary, we have identified two major pathways that control perineural and cortex gliogenesis in the post-embryonic brain and have shown that the molecular circuitry required is lineage specific.

Local generation of glia is a major astrocyte source in postnatal cortex

Glial cells constitute nearly 50% of the cells in the human brain. Astrocytes, which make up the largest glial population, are crucial to the regulation of synaptic connectivity during postnatal development. Because defects in astrocyte generation are associated with severe neurological disorders such as brain tumours, it is important to understand how astrocytes are produced. Astrocytes reportedly arise from two sources: radial glia in the ventricular zone and progenitors in the subventricular zone, with the contribution from each region shifting with time. During the first three weeks of postnatal development, the glial cell population, which contains predominantly astrocytes, expands 6-8-fold in the rodent brain. Little is known about the mechanisms underlying this expansion. Here we show that a major source of glia in the postnatal cortex in mice is the local proliferation of differentiated astrocytes. Unlike glial progenitors in the subventricular zone, differentiated astrocytes undergo symmetric division, and their progeny integrate functionally into the existing glial network as mature astrocytes that form endfeet with blood vessels, couple electrically to neighbouring astrocytes, and take up glutamate after neuronal activity.

Drosophila miR-124 regulates neuroblast proliferation through its target anachronism

MicroRNAs (miRNAs) have been implicated as regulators of central nervous system (CNS) development and function. miR-124 is an evolutionarily ancient, CNS-specific miRNA. On the basis of the evolutionary conservation of its expression in the CNS, miR-124 is expected to have an ancient conserved function. Intriguingly, investigation of miR-124 function using antisense-mediated miRNA depletion has produced divergent and in some cases contradictory findings in a variety of model systems. Here we investigated miR-124 function using a targeted knockout mutant and present evidence for a role during central brain neurogenesis in Drosophila melanogaster. miR-124 activity in the larval neuroblast lineage is required to support normal levels of neuronal progenitor proliferation. We identify anachronism (ana), which encodes a secreted inhibitor of neuroblast proliferation, as a functionally important target of miR-124 acting in the neuroblast lineage. ana has previously been thought to be glial specific in its expression and to act from the cortex glia to control the exit of neuroblasts from quiescence into the proliferative phase that generates the neurons of the adult CNS during larval development. We provide evidence that ana is expressed in miR-124-expressing neuroblast lineages and that ana activity must be limited by the action of miR-124 during neuronal progenitor proliferation. We discuss the possibility that the apparent divergence of function of miR-124 in different model systems might reflect functional divergence through target site evolution.

TRPV1-Dependent and -Independent Alterations in the Limbic Cortex of Neuropathic Mice: Impact on Glial Caspases and Pain Perception

During neuropathic pain, caspases are activated in the limbic cortex. We investigated the role of TRPV1 channels and glial caspases in the mouse prelimbic and infralimbic (PL-IL) cortex after spared nerve injury (SNI). Reverse transcriptase-polymerase chain reaction, western blots, and immunfluorescence showed overexpression of several caspases in the PL-IL cortex 7 days postinjury. Caspase-3 release and upregulation of AMPA receptors in microglia, caspase-1 and IL-1β release in astrocytes, and upregulation of Il-1 receptor-1, TRPV1, and VGluT1 in glutamatergic neurons, were also observed. Of these alterations, only those in astrocytes persisted in SNI Trpv1(-/-) mice. A pan-caspase inhibitor, injected into the PL-IL cortex, reduced mechanical allodynia, this effect being reduced but not abolished in Trpv1(-/-) mice. Single-unit extracellular recordings in vivo following electrical stimulation of basolateral amygdala or application of pressure on the hind paw, showed increased excitatory pyramidal neuron activity in the SNI PL-IL cortex, which also contained higher levels of the endocannabinoid 2-arachidonoylglycerol. Intra-PL-IL cortex injection of mGluR5 and NMDA receptor antagonists and AMPA exacerbated, whereas TRPV1 and AMPA receptor antagonists and a CB(1) agonist inhibited, allodynia. We suggest that SNI triggers both TRPV1-dependent and independent glutamate- and caspase-mediated cross-talk among IL-PL cortex neurons and glia, which either participates or counteracts pain.

A morphometric study of glia and neurons in the anterior cingulate cortex in mood disorder

The anterior cingulate cortex (ACC) is a key region for the pathophysiology and treatment of depression. However, it remains unclear whether and how the morphology of the ACC is altered in subjects with mood disorders. A post mortem morphometric study of the supragenual ACC (Brodmann area 24b) in seven subjects with mood disorder and nine comparison subjects. We measured glial and neuronal density, and neuronal size and shape. We also quantified the astrocytic marker, glial fibrillary acidic protein (GFAP), using immunoautoradiography. Cortical and layer thickness did not differ between groups. Subjects with mood disorder had a decreased density of glial cells across all layers, and a reduction in GFAP in white matter. The density of pyramidal neurons was decreased selectively in layer Vb, and their size was increased in layers V and VI. The shape of pyramidal neurons also differed in mood disorder, in layers Va and VI. These data provide further evidence for morphometric alterations in glia and pyramidal neurons in mood disorder. They represent a possible cellular basis for the aberrant functioning and connectivity of the ACC apparent from neuroimaging and other studies.

Morphological diversity and development of glia in Drosophila

Insect glia represents a conspicuous and diverse population of cells and plays a role in controlling neuronal progenitor proliferation, axonal growth, neuronal differentiation and maintenance, and neuronal function. Genetic studies in Drosophila have elucidated many aspects of glial structure, function, and development. Just as in vertebrates, it appears as if different classes of glial cells are specialized for different functions. On the basis of topology and cell shape, glial cells of the central nervous system fall into three classes (Fig. 1A-C): (i) surface glia that extend sheath-like processes to wrap around the entire brain; (ii) cortex glia (also called cell body-associated glia) that encapsulate neuronal somata and neuroblasts which form the outer layer (cortex) of the central nervous system; (iii) neuropile glia that are located at the interface between the cortex and the neuropile, the central domain of the nervous system formed by the highly branched neuronal processes and their synaptic contacts. Surface glia is further subdivided into an outer, perineurial layer, and an inner, subperineurial layer. Likewise, neuropile glia comprises a class of cells that remain at the surface of the neuropile (ensheathing glia), and a second class that forms profuse lamellar processes around nerve fibers within the neuropile (astrocyte-like or reticular glia). Glia also surrounds the peripheral nerves and sensory organs; here, one also recognizes perineurial and subperineurial glia, and a third type called "wrapping glia" that most likely corresponds to the ensheathing glia of the central nervous system. Much more experimental work is needed to determine how fundamental these differences between classes of glial cells are, or how and when during development they are specified. To aid in this work the following review will briefly summarize our knowledge of the classes of glial cells encountered in the Drosophila nervous system, and then survey their development from the embryo to adult.

Drosophila cortex and neuropile glia influence secondary axon tract growth, pathfinding, and fasciculation in the developing larval brain

Glial cells play important roles in the developing brain during axon fasciculation, growth cone guidance, and neuron survival. In the Drosophila brain, three main classes of glia have been identified including surface, cortex, and neuropile glia. While surface glia ensheaths the brain and is involved in the formation of the blood-brain-barrier and the control of neuroblast proliferation, the range of functions for cortex and neuropile glia is less well understood. In this study, we use the nirvana2-GAL4 driver to visualize the association of cortex and neuropile glia with axon tracts formed by different brain lineages and selectively eliminate these glial populations via induced apoptosis. The larval central brain consists of approximately 100 lineages. Each lineage forms a cohesive axon bundle, the secondary axon tract (SAT). While entering and traversing the brain neuropile, SATs interact in a characteristic way with glial cells. Some SATs are completely invested with glial processes; others show no particular association with glia, and most fall somewhere in between these extremes. Our results demonstrate that the elimination of glia results in abnormalities in SAT fasciculation and trajectory. The most prevalent phenotype is truncation or misguidance of axon tracts, or abnormal fasciculation of tracts that normally form separate pathways. Importantly, the degree of glial association with a given lineage is positively correlated with the severity of the phenotype resulting from glial ablation. Previous studies have focused on the embryonic nerve cord or adult-specific compartments to establish the role of glia. Our study provides, for the first time, an analysis of glial function in the brain during axon formation and growth in larval development.

Organization and postembryonic development of glial cells in the adult central brain of Drosophila.

Glial cells exist throughout the nervous system, and play essential roles in various aspects of neural development and function. Distinct types of glia may govern diverse glial functions. To determine the roles of glia requires systematic characterization of glia diversity and development. In the adult Drosophila central brain, we identify five different types of glia based on its location, morphology, marker expression, and development. Perineurial and subperineurial glia reside in two separate single-cell layers on the brain surface, cortex glia form a glial mesh in the brain cortex where neuronal cell bodies reside, while ensheathing and astrocyte-like glia enwrap and infiltrate into neuropils, respectively. Clonal analysis reveals that distinct glial types derive from different precursors, and that most adult perineurial, ensheathing, and astrocyte-like glia are produced after embryogenesis. Notably, perineurial glial cells are made locally on the brain surface without the involvement of gcm (glial cell missing). In contrast, the widespread ensheathing and astrocyte-like glia derive from specific brain regions in a gcm-dependent manner. This study documents glia diversity in the adult fly brain and demonstrates involvement of different developmental programs in the derivation of distinct types of glia. It lays an essential foundation for studying glia development and function in the Drosophila brain.

Oestrogen and Progesterone Reduce Lipopolysaccharide‐Induced Expression of Tumour Necrosis Factor‐α and Interleukin‐18 in Midbrain Astrocytes

Besides microglia, astrocytes exert an important regulatory function in the initiation and control of neuro-inflammatory processes in the central nervous system. Clinical and experimental data suggest that sex steroids are neuroprotective and that neurological/neurodegenerative disorders display sex-specific characteristics. Astroglia is known to respond to toxic stimuli by secretion of distinct pro-inflammatory/apoptotic cytokines. In the present study, we investigated the influence of oestrogen and progesterone on the expression of the cytokines tumour necrosis factor (TNF)-alpha and interleukin (IL)-18 in primary astrocytes obtained from neonatal mouse midbrain and cerebral cortex after the stimulation with lipopolysaccharides (LPS). LPS strongly induced the expression of TNF-alpha in astrocytes from both brain regions and IL-18 in those from midbrain. Oestrogen significantly attenuated LPS-induced TNF-alpha expression in the midbrain glia but not in the cortex glia. Combined treatment with oestrogen and progesterone together diminished LPS-induced IL-18 expression in the midbrain completely. Both steroid effects could be specifically antagonised by the steroid hormone receptor antagonists ICI 182 780 and mifepristone. We conclude that neuroprotective oestrogen and progesterone effects in the midbrain might be in part the consequence of a reduced pro-inflammatory response of astroglia.

P2Y1receptor switches to neurons from glia in juvenile versus neonatal rat cerebellar cortex

BackgroundIn the CNS, several P2 receptors for extracellular nucleotides are identified on neurons and glial cells to participate to neuron-neuron, glia-glia and glia-neuron communication.ResultsIn this work, we describe the cellular and subcellular presence of metabotropic P2Y1 receptor in rat cerebellum at two distinct developmental ages, by means of immunofluorescence-confocal and electron microscopy as well as western blotting and direct membrane separation techniques. At postnatal day 21, we find that P2Y1 receptor in addition to Purkinje neurons, is abundant on neuronal specializations identified as noradrenergic by anatomical, morphological and biochemical features. P2Y1 receptor immunoreactivity colocalizes with dopamine β-hydroxylase, tyrosine hydroxylase, neurofilament light chain, synaptophysin and flotillin, but not with glial fibrillary acidic protein for astrocytes. P2Y1 receptor is found enriched in membrane microdomains such as lipid rafts, in cerebellar synaptic vesicles, and is moreover visualized on synaptic varicosities by electron microscopy analysis. When examined at postnatal day 7, P2Y1 receptor immunoreactivity is instead predominantly expressed only on Bergmann and astroglial cells, as shown by colocalization with glial fibrillary acidic protein rather then neuronal markers. At this age, we moreover identify that P2Y1 receptor-positive Bergmann fibers wrap up doublecortin-positive granule cells stretching along them, while migrating through the cerebellar layers.ConclusionMembrane components including purinergic receptors are already known to mediate cellular contact and aggregation in platelets. Our results suggesting a potential role for P2Y1 protein in cell junction/communication and development, are totally innovative for the CNS.

Chronic Unpredictable Stress Decreases Cell Proliferation in the Cerebral Cortex of the Adult Rat

One of the most consistent morphologic findings in postmortem studies of brain tissue from depressed patients is a decrease in the number of glia in the prefrontal cortex. However, little is known about the mechanisms that contribute to this decrease in cell number. To address this question, we subjected adult rats to chronic stress, a vulnerability factor for depression, and measured cell proliferation as a potential cellular mechanism that could underlie glial reduction in depression. We found that exposure to chronic unpredictable stress (CUS) for 15 days significantly decreased cell proliferation in neocortex by approximately 35%. This effect was dependent on the duration, intensity and type of stress, and was region-specific. Analysis of cell phenotype demonstrated that there was a decrease in the number of oligodendrocytes and endothelial cells. Finally, using a CUS paradigm that allows for analysis of anhedonia, we found that chronic antidepressant administration reversed the decrease in cortical cell proliferation, as well as the deficit in sucrose preference. These findings are consistent with the possibility that decreased cell proliferation could contribute to reductions in glia in prefrontal cortex of depressed subjects and further elucidate the cellular actions of stress and antidepressants.

Glutamine and Glutamate Levels in Children and Adolescents With Bipolar Disorder: A 4.0-T Proton Magnetic Resonance Spectroscopy Study of the Anterior Cingulate Cortex

The purpose of this study was to use proton magnetic resonance spectroscopy, at 4.0 T, to explore the glutamine and glutamate levels in the anterior cingulate cortex of children and adolescents with bipolar disorder (BPD; medicated and unmedicated) and healthy comparison subjects (HCSs). We hypothesized that unmedicated children with BPD would have reduced glutamine and glutamate levels compared with HCSs and medicated children with BPD. Spectra were acquired from the anterior cingulate cortex in 22 children and adolescents with DSM-IV-TR BPD, type 1 (13 female: age 12.6 +/- 4.4 years: 7 of the subjects with BPD were unmedicated at the time of the scan) and 10 HCSs (7 female: age 12.3 +/- 2.5 years). Unmedicated subjects with BPD had significantly lower glutamine levels than HCSs or medicated subjects with BPD. There were no differences in glutamate levels between the three groups. These results are consistent with there being an abnormality in anterior cingulate cortex glia in untreated children and adolescents with BPD. The results of this pilot study may be important in helping us better understand the pathophysiology of child and adolescent BPD. In addition, this observation may help to develop better and more targeted treatments, in particular those affecting the metabolism of glutamine, perhaps by regulation of glutamine synthetase activity.

Morphogenesis and proliferation of the larval brain glia in Drosophila

Glial cells subserve a number of essential functions during development and function of the Drosophila brain, including the control of neuroblast proliferation, neuronal positioning and axonal pathfinding. Three major classes of glial cells have been identified. Surface glia surround the brain externally. Neuropile glia ensheath the neuropile and form septa within the neuropile that define distinct neuropile compartments. Cortex glia form a scaffold around neuronal cell bodies in the cortex. In this paper we have used global glial markers and GFP-labeled clones to describe the morphology, development and proliferation pattern of the three types of glial cells in the larval brain. We show that both surface glia and cortex glia contribute to the glial layer surrounding the brain. Cortex glia also form a significant part of the glial layer surrounding the neuropile. Glial cell numbers increase slowly during the first half of larval development but show a rapid incline in the third larval instar. This increase results from mitosis of differentiated glia, but, more significantly, from the proliferation of neuroblasts.

Time course and sequence of pathological changes in the cerebellum of microsphere-embolized rats

Ischemia is a major cause of damage to the central nervous system as a consequence of stroke or trauma. Here, we analyzed with high temporal resolution the time course of pathological changes in the neurons (granule and Purkinje cells) and glia (Bergmann and astroglia cells) in the cerebellar cortex and white matter. The period studied ranged from 30 min to 7 days after a microsphere-induced embolism used as a model of stroke and multi-infarct dementia. Some pathological changes in the neurons in the cerebellar cortex were identified early, that is, beginning at 3 h after the microsphere-induced embolism, and glial pathology appeared only later. The pathological changes in the white matter also appeared slightly later, that is, 6 h after embolism and were less pronounced than those in the cerebellar cortex. This suggests that neuronal pathology is induced more rapidly and/or more easily than the glial pathology. In addition, BrdU staining shows that cell proliferation is limited to a 1-day period beginning about 1 day after the embolism. These data demonstrate that changes after an ischemic lesion of the cerebellum proceeds from upper cerebellar cortex to deeper cerebellar cortex or white matter and also that microsphere-induced changes proceed from neuronal to glial pathology.

Role of DE-Cadherin in Neuroblast Proliferation, Neural Morphogenesis, and Axon Tract Formation inDrosophilaLarval Brain Development

In the wild-type brain, the Drosophila classic cadherin DE-cadherin is expressed globally by postembryonic neuroblasts and their lineages ("secondary lineages"), as well as glial cells. To address the role of DE-cadherin in the larval brain, we took advantage of the dominant-negative DE-cad(ex) construct, the expression of which was directed to neurons, glial cells, or both. Global expression of DE-cad(ex) driven by a heat pulse during the early second instar resulted in a severe phenotype that included deficits in neural proliferation. Neuroblasts appeared in approximately normal numbers but had highly reduced mitotic activity. When the DE-cad(ex) construct was driven by the glial-specific driver gcm-Gal4, the effect of DE-cad(ex) on neuroblast proliferation could be replicated, which indicates that DE-cadherin acts in glial cells to promote proliferation of neuroblasts. Expression of DE-cad(ex) in neurons, cortex glia, or both results in abnormalities in cortex layering and in trajectories of secondary axons. In the wild-type brain, neuroblasts and neurons generated at different time points are arranged concentrically around the neuropile, with the DE-cadherin-positive neuroblasts and young secondary neurons at the surface, followed by older secondary neurons and primary neurons. Axons of secondary lineages follow a straight radial course toward the neuropile. Processes of glial cells located in the cortex form a scaffold, called trophospongium, that enwraps neuroblasts and neurons. Expression of DE-cad(ex) in neurons, cortex glia, or both disrupted the regular placement of neuroblasts and secondary neurons and resulted in abnormal trajectories of cell body fiber tracts. We conclude that DE-cadherin plays a pivotal role in larval brain proliferation, brain cortex morphogenesis, and axon growth.