Roles of the mammalian subventricular zone in brain development

Cell proliferation in human ganglionic eminence and suppression after prematurity-associated haemorrhage

In premature infants, germinal matrix haemorrhage in the brain is a common occurrence. However, cell proliferation and fate determination in the normal human germinal matrix is poorly understood. Human ganglionic eminence samples were collected prospectively from autopsies of premature and term infants with no evidence of pathological process (n=78; dying at post-menstrual age 14-88 weeks). The ganglionic eminence was thickest at 20-26 weeks and involuted by 34-36 weeks. Proliferating cells, detected by Ki67 immunoreactivity, were abundant throughout the ganglionic eminence prior to 18 weeks, after which a sharp boundary between the dorsal and ventral ganglionic eminence appeared with reduced cell proliferation in the dorsal region. Ki67 immunoreactivity persisted in the majority of ventral cells until ∼28 weeks, after which time the proportion of proliferating cells dropped quickly. The expression of cell lineage markers (such as Olig2, SOX2, platelet-derived growth factor receptor alpha) showed partitioning at the microscopic level. The hypothesis that germinal matrix haemorrhage suppresses cell proliferation was then addressed. In comparison to controls, germinal matrix haemorrhage (n=47; born at post-menstrual age 18-34 weeks followed by survival of 0 h to 98 days) was associated with significantly decreased cell proliferation if survival was >12 h. The cell cycle arrest transcription factor p53 was transiently increased and the oligodendroglial lineage markers Olig2 and platelet-derived growth factor receptor alpha were decreased. Cell death was negligible. A low level of microglial activation was detected. Haemorrhage-associated suppression of cell proliferation in premature human infants could partially explain the reduced brain size and clinical effects in children who suffer germinal matrix haemorrhage after premature birth.

Viral infection and neural stem/progenitor cell's fate: implications in brain development and neurological disorders

Viral infections in the prenatal (during pregnancy) and perinatal period have been a common cause of brain malformation. Besides the immediate neurological dysfunctions, virus infections may critically affect CNS development culminating in long-term cognitive deficits. Most of these neurotropic viruses are most damaging at a critical stage of the host, when the brain is in a dynamic stage of development. The neuropathology can be attributed to the massive neuronal loss induced by the virus as well as lack of CNS repair owing to a deficit in the neural stem/progenitor cell (NSPC) pool or aberrant formation of new neurons from NSPCs. Being one of the mitotically active populations in the post natal brain, the NSPCs have emerged as the potential targets of neurotropic viruses. The NSPCs are self-renewing and multipotent cells residing in the neurogenic niches of the brain, and, therefore, hampering the developmental fate of these cells may adversely affect the overall neurogenesis pattern. A number of neurotropic viruses utilize NSPCs as their cellular reservoirs and often establish latent and persistent infection in them. Both HIV and Herpes virus infect NSPCs over long periods of time and reactivation of the virus may occur later in life. The virus infected NSPCs either undergoes cell cycle arrest or impaired neuronal or glial differentiation, all of which leads to impaired neurogenesis. The disturbances in neurogenesis and CNS development following neurotropic virus infections have direct implications in the viral pathogenesis and long-term neurobehavioral outcome in infected individuals.

Widespread proliferation impairment and hypocellularity in the cerebellum of fetuses with down syndrome

Evidence in mouse models for Down syndrome (DS) and human fetuses with DS clearly shows severe neurogenesis impairment in various telencephalic regions, suggesting that this defect may underlie the cognitive abnormalities of DS. As cerebellar hypotrophy and motor disturbances are part of the clinical features of DS, the goal of our study was to establish whether these defects may be related to neurogenesis impairment during cerebellar development. We found that in fetuses with DS (17-21 weeks of gestation) the cerebellum had an immature pattern, a reduced volume and notably fewer cells (-25%/-50%) in all cerebellar layers. Immunohistochemistry for Ki-67, a marker of cycling cells, showed impaired proliferation (-17%/-50%) of precursors from both cerebellar neurogenic regions (external granular layer and ventricular zone). No differences in apoptotic cell death were found in DS vs. control fetuses. The current study provides novel evidence that in the cerebellum of DS fetuses there is a generalized hypocellularity and that this defect is due to proliferation impairment, rather than to an increased cell death. The reduced proliferation potency found in the DS fetal cerebellum, in conjunction with previous evidence, strengthens the idea that the trisomic brain is characterized by widespread neurogenesis disruption.

A role for intermediate radial glia in the tangential expansion of the mammalian cerebral cortex

The cerebral cortex of large mammals undergoes massive surface area expansion and folding during development. Specific mechanisms to orchestrate the growth of the cortex in surface area rather than in thickness are likely to exist, but they have not been identified. Analyzing multiple species, we have identified a specialized type of progenitor cell that is exclusive to mammals with a folded cerebral cortex, which we named intermediate radial glia cell (IRGC). IRGCs express Pax6 but not Tbr2, have a radial fiber contacting the pial surface but not the ventricular surface, and are found in both the inner subventricular zone and outer subventricular zone (OSVZ). We find that IRGCs are massively generated in the OSVZ, thus augmenting the numbers of radial fibers. Fanning out of this expanding radial fiber scaffold promotes the tangential dispersion of radially migrating neurons, allowing for the growth in surface area of the cortical sheet. Accordingly, the tangential expansion of particular cortical regions was preceded by high proliferation in the underlying OSVZ, whereas the experimental reduction of IRGCs impaired the tangential dispersion of neurons and resulted in a smaller cortical surface. Thus, the generation of IRGCs plays a key role in the tangential expansion of the mammalian cerebral cortex.

Early pharmacotherapy restores neurogenesis and cognitive performance in the Ts65Dn mouse model for Down syndrome

Down syndrome (DS) is a genetic pathology characterized by intellectual disability and brain hypotrophy. Widespread neurogenesis impairment characterizes the fetal and neonatal DS brain, strongly suggesting that this defect may be a major determinant of mental retardation. Our goal was to establish, in a mouse model for DS, whether early pharmacotherapy improves neurogenesis and cognitive behavior. Neonate Ts65Dn mice were treated from postnatal day (P) 3 to P15 with fluoxetine, an antidepressant that inhibits serotonin (5-HT) reuptake and increases proliferation in the adult Ts65Dn mouse (Clark et al., 2006). On P15, they received a BrdU injection and were killed after either 2 h or 1 month. Results showed that P15 Ts65Dn mice had notably defective proliferation in the hippocampal dentate gyrus, subventricular zone, striatum, and neocortex and that proliferation was completely rescued by fluoxetine. In the hippocampus of untreated P15 Ts65Dn mice, we found normal 5-HT levels but a lower expression of 5-HT1A receptors and brain-derived neurotrophic factor (BDNF). In Ts65Dn mice, fluoxetine treatment restored the expression of 5-HT1A receptors and BDNF. One month after cessation of treatment, there were more surviving cells in the dentate gyrus of Ts65Dn mice, more cells with a neuronal phenotype, more proliferating precursors, and more granule cells. These animals were tested for contextual fear conditioning, a hippocampus-dependent memory task, and exhibited a complete recovery of memory performance. Results show that early pharmacotherapy with a drug usable by humans can correct neurogenesis and behavioral impairment in a model for DS.

Expression of vascular endothelial growth factor receptor-3 mRNA in the rat developing forebrain and retina

Vascular endothelial growth factor receptor (VEGFR)-3, a receptor for VEGF-C and VEGF-D, is expressed in neural progenitor cells, but there has been no comprehensive study of its distribution in the developing brain. Here, the temporal and cell-specific expression of VEGFR-3 mRNA was studied in the developing rat forebrain and eye. Expression appeared along the ventricular and subventricular zones of the lateral and third ventricles showing ongoing neurogenesis as early as embryonic day 13 but was progressively down-regulated during development and remained in the subventricular zone and rostral migratory stream of the adult forebrain. VEGFR-3 expression was also detectable in some differentiating and postmitotic neurons in the developing cerebral cortex, including Cajal-Retzius cells, cortical plate neurons, and subplate neurons. Expression in the subplate increased significantly during the early postnatal period but was absent by postnatal day 14. It was also highly expressed in nonneural tissues of the eye during development, including the retinal pigment epithelium, the retinal ciliary margin, and the lens, but persisted in a subset of cells in the pigmented ciliary epithelium of the adult eye. In contrast, there was weak or undetectable expression in the early neural retina, but a subset of retinal neurons in the postnatal and mature retina showed intense signals. These unique spatiotemporal mRNA expression patterns suggest that VEGFR-3 might mediate the regulation of both neurogenesis and adult neuronal function in the rat forebrain and eye.

Ikaros-1 couples cell cycle arrest of late striatal precursors with neurogenesis of enkephalinergic neurons

During central nervous system development, several transcription factors regulate the differentiation of progenitor cells to postmitotic neurons. Here we describe a novel role for Ikaros-1 in the generation of late-born striatal neurons. Our results show that Ikaros-1 is expressed in the boundary of the striatal germinal zone (GZ)/mantle zone (MZ), where it induces cell cycle arrest of neural progenitors by up-regulation of the cyclin-dependent kinase inhibitor (CDKi) p21(Cip1/Waf1). This effect is coupled with the neuronal differentiation of late precursors, which in turn is critical for the second wave of striatal neurogenesis that gives rise to matrix neurons. Consistently, Ikaros(-/-) mice had fewer striatal projecting neurons and, in particular, enkephalin (ENK)-positive neurons. In addition, overexpression of Ikaros-1 in primary striatal cultures increases the number of calbindin- and ENK-positive neurons. Our results also show that Ikaros-1 acts downstream of the Dlx family of transcription factors, insofar as its expression is lost in Dlx1/2 double knockout mice. However, we demonstrate that Ikaros-1 and Ebf-1 independently regulate the final determination of the two populations of striatal projection neurons of the matrix compartment, ENK- and substance P-positive neurons. In conclusion, our findings identify Ikaros-1 as a modulator of cell cycle exit of neural progenitors that gives rise to the neurogenesis of ENK-positive striatal neurons.

The cerebral cortex overlying periventricular leukomalacia: analysis of pyramidal neurons

The role of the cerebral cortex in the cognitive deficits in preterm survivors is poorly understood. Periventricular leukomalacia (PVL), the key feature of encephalopathy of prematurity, is characterized by periventricular necrotic foci and diffuse gliosis in the surrounding cerebral white matter. Here, we tested the hypothesis that reductions in the density of layer I neurons and/or pyramidal neurons in layers III and/or V are associated with PVL, indicating cortical pathology potentially associated with cognitive deficits in long-term survivors. In controls (23 gestational weeks to 18 postnatal months) (n = 15), a lack of significant differences in pyramidal density among incipient Brodmann areas suggested that cytoarchitectonic differences across functional areas are not fully mature in the fetal and infant periods. There was a marked reduction (38%) in the density of layer V neurons in all areas sampled in the PVL cases (n = 17) compared to controls (n = 12) adjusted for postconceptional age at or greater than 30 weeks, when the six-layer cortex is visually distinct (P < 0.024). This may reflect a dying-back loss of somata complicating transection of layer V axons projecting through the necrosis in the underlying white matter. This study underscores the potential role of secondary cortical injury in the encephalopathy of prematurity.

Hypoxia stimulates proliferation of rat neural stem cells with influence on the expression of cyclin D1 and c-Jun N-terminal protein kinase signaling pathway in vitro

Ischemia/hypoxia is known to induce the neural stem cells proliferation and neural differentiation in rodent and human brain; however its mechanisms remain largely unknown. In this study we investigated the effect of hypoxia on neural stem cells (NSCs) proliferation with the expression of cyclin D1 and the phosphorylation of mitogen-activated protein kinases (MAPK) signaling molecules. NSCs were cultured from cortex of fetal Sprague-Dawley rats on embryonic day 5.5. The hypoxia was made using a microaerophilic incubation system. The NSCs proliferation was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, diameter measurement of neurospheres, bromodeoxyuridine (BrdU) incorporation assay and cell cycle analysis. The cell death of NSCs was evaluated by terminal dUTP nick-end labeling (TUNEL) assay. The expression of cyclin D1, phosphorylated extracellular signal regulated kinase (ERK), c-Jun N-terminal protein kinase (JNK) and p38 were analyzed by immunoblotting assay. The results showed that hypoxia increased NSCs proliferation in cell amount, diameter of neurospheres, BrdU incorporation and cell division, and the highest proliferation of the NSCs was observed with 12 h hypoxic treatment; hypoxia did not decrease cell death of NSCs; after hypoxic treatment, the expression of cyclin D1 increased, meanwhile P-JNK2 level increased, P-p38 decreased, and no significant change in P-ERK2 level compared to normoxic cultures. JNK inhibitor SP600125 attenuated the increase of cyclin D1 induced by hypoxia. These findings propose that hypoxia increases cyclin D1 expression through activation of JNK in NSCs of rat in vitro, suggesting a novel possible mechanism for hypoxia-induced proliferation of NSCs.

In vivo MRI of endogenous stem/progenitor cell migration from subventricular zone in normal and injured developing brains

Understanding the alterations of migratory activities of the endogenous neural stem/progenitor cells (NSPs) in injured developing brains is becoming increasingly imperative for curative reasons. In this study, 10-day-old neonatal rats with and without hypoxic-ischemic (HI) insult at postnatal day 7 were injected intraventricularly with micron-sized iron oxide particles (MPIOs), followed by serial high-resolution MRI at 7 T for 2 weeks. MRI findings were correlated to the histological analysis using iron staining and several immunohistochemical double staining. The results indicated that in normal and HI-injured brains the NSPs from the subventricular zone (SVZ) were labeled by MPIOs, and migrated as newly created cells (iron+/BrdU+), neuroblasts (iron+/nestin+), astrocytes or astrocytes-like progenitor cells (iron+/GFAP+), and mature neurons (iron+/NeuN+). In normal brains, the endogenous NSPs mainly exhibited a tangential pattern in both rostral and caudal directions. The NSP radial migratory pattern could be observed in some rats. In the HI-injured brains during the same developmental period, the NSPs mainly migrated towards the HI lesion sites. The tangential, rostrocaudal migrations could be observed but impaired. These findings suggest that the NSP migratory pathways in SVZ change in response to the HI insult, likely due to the self-repairing efforts known in the neonatal brains. The MRI approach demonstrated here is potentially applicable to the in vivo and longitudinal study of NSP cell activities in developing brains under normal and pathological conditions and in therapeutic interventions.

The presenilin-1 familial Alzheimer's disease mutation P117L decreases neuronal differentiation of embryonic murine neural progenitor cells

The presenilin-1 gene is mutated in early-onset familial Alzheimer's disease. The mutation Pro117Leu is implicated in a very severe form of the disease, with an onset of less than 30 years. The consequences of this mutation on neurogenesis in the hippocampus of adult transgenic mice have already been studied in situ. The survival of neural progenitor cells was impaired resulting in decreased neurogenesis in the dentate gyrus. Our intention was to verify if similar alterations could occur in vitro in progenitor cells from the murine ganglionic eminences isolated from embryos of this same transgenic mouse model. These cells were grown in culture as neurospheres and after differentiation the percentage of neurons generated as well as their morphology were analysed. The mutation results in a significant decrease in neurogenesis compared to the wild type mice and the neurons grow longer and more ramified neurites. A shift of differentiation towards gliogenesis was observed that could explain decreased neurogenesis despite increased proliferation of neural precursors in transgenic neurospheres. A diminished survival of the newly generated mutant neurons is also proposed. Our data raise the possibility that these alterations in embryonic development might contribute to increase the severity of the Alzheimer's disease phenotype later in adulthood.

Basic fibroblast growth factor stimulates the proliferation and differentiation of neural stem cells in neonatal rats after ischemic brain injury

A little is known about the proliferation and fate of neural stem cells in the subventricular zone (SVZ) after cerebral ischemia. However, how endogenous neural stem cells are activated in the premature brain is not clear, although basic fibroblast growth factor (bFGF) is important in neurogenesis. To investigate the effect of bFGF on the proliferation and differentiation of neural stem cells after brain ischemia, we observed cellular changes in the subventricular zone (SVZ) of 3-day-old rats (approximately equivalent to premature infants) using immunofluorescence assays, Western blot analysis, and real-time quantitative PCR methods. The bilateral common carotid artery (BCCA) was occluded in 108 animals, then half received bFGF 10ng/g. Besides, 54 rats without ischemia as normal control. Proliferating cells were labeled by bromodeoxyuridine (BrdU) through intraperitoneal injection in a pulsed or a cumulative protocol. Rats were killed at 4, 7, and 14 days after ischemic injury. The number of proliferating cells in the SVZ in bFGF-treated rats was higher than that in untreated rats; bFGF also promoted neural stem cell differentiation into neurons, astrocytes, and oligodendrocytes. Western blot analysis and real-time quantitative PCR assays confirmed these results. We suggest that bFGF promotes the repair of ischemia brain injury through increasing the proliferation of neural stem cells and their differentiation into neurons, astrocytes, and oligodendrocytes.

Patterns of p57Kip2 expression in embryonic rat brain suggest roles in progenitor cell cycle exit and neuronal differentiation

In developing central nervous system, a variety of mechanisms couple cell cycle exit to differentiation during neurogenesis. The cyclin-dependent kinase (CDK) inhibitor p57Kip2 controls the transition from proliferation to differentiation in many tissues, but roles in developing brain remain uncertain. To characterize possible functions, we defined p57Kip2 protein expression in embryonic (E) day 12.5 to 20.5 rat brains using immunohistochemistry combined with markers of proliferation and differentiation. The p57Kip2 was localized primarily in cell nuclei and positive cells formed two distinct patterns including wide dispersion and laminar aggregation that were brain region-specific. From E12.5 to E16.5, p57Kip2 expression was detected mainly in ventricular zone (VZ) and/or mantle zone of hippocampus, septum, basal ganglia, thalamus, hypothalamus, midbrain, and spinal cord. After E18.5, p57Kip2 was detected in select regions undergoing differentiation. The p57Kip2 expression was also compared with regional transcription factors, including Ngn2, Nkx2.1, and Pax6. Time course studies performed in diencephalon showed that p57Kip2 immunoreactivity colocalized with BrdU at 8 hr in nuclei exhibiting the wide dispersion pattern, whereas colocalization in the laminar pattern occurred only later. Moreover, p57Kip2 frequently colocalized with neuronal marker, beta-III tubulin. Finally, we characterized relationships of p57Kip2 to CDK inhibitor p27Kip1: in proliferative regions, p57Kip2 expression preceded p27Kip1 as cells underwent differentiation, though the proteins colocalized in substantial numbers of cells, suggesting potentially related yet distinct functions of Cip/Kip family members during neurogenesis. Our observations that p57Kip2 exhibits nuclear expression as precursors exit the cell cycle and begin expressing neuronal characteristics suggests that the CDK inhibitor contributes to regulating the transition from proliferation to differentiation during brain development.

Lithium restores neurogenesis in the subventricular zone of the Ts65Dn mouse, a model for Down syndrome

Down syndrome (DS), a high-incidence genetic pathology, involves brain hypoplasia and mental retardation. Emerging evidence suggests that reduced neurogenesis may be a major determinant of brain underdevelopment in DS. To establish whether it is possible to improve neurogenesis in DS, Ts65Dn mice--the most widely used model for DS--and euploid mice were treated with control or lithium chow for 1 month. During the last 3 days animals received one daily injection of 5-bromo-2-deoxyuridine (BrdU)--a marker of proliferating cells--and were sacrificed 24 h after the last injection. Neurogenesis was examined in the subventricular zone (SVZ), a region that retains a neurogenic potential across life. We found that Ts65Dn mice had less (-40%) BrdU+ cells than euploid mice, indicating severe proliferation impairment. Treatment with lithium increased the number of Brdu+ cells in both euploid and Ts65Dn mice. In the latter the number of Brdu+ cells became similar to that of untreated euploid mice. Our study shows that lithium is able to restore cell proliferation in the SVZ of the Ts65Dn mouse and point at treatments with mood stabilizers as a potential tool to improve neurogenesis in patients with DS.

Experimental neuronal migration disorders following the administration of ibotenate in hamsters: the role of the subventricular zone in the development of cortical dysplasia

To examine the role of subventricular zone in cortical dysplasia, an experimental model was established using a neuronal tracing study. Ibotenate is a glutamate receptor agonist, and its intracerebral injection produces excitotoxic lesions mimicking microgyria and heterotopia. A total of 72 newborn hamsters were subjected. Biotinylated dextran amine was injected into the ganglionic eminence for the neuronal tracer. The cortical lesions and apoptotic cells were analyzed. In the microgyric cortex, terminal deoxynucleotidyl transferase-mediated 2' -deoxyuridine 5'-triphosphate-biotin end labeling-positive cells were increased and accumulated in the cortical folding. Biotinylated dextran amine-positive cells and fibers were derived from the dorsolateral subventricular zone and directed toward the cortical folding. In the heterotopic cortex, terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate- biotin end labeling-positive cells were distributed around the heterotopia, but number of cells was not remarkable. Our findings suggest that the subventricular zone plays an important role in the formation of cortical dysplasia, especially in the microgyria, after excitatory neuronal injury.

Brain injury in premature infants: a complex amalgam of destructive and developmental disturbances

Brain injury in premature infants is of enormous public health importance because of the large number of such infants who survive with serious neurodevelopmental disability, including major cognitive deficits and motor disability. This type of brain injury is generally thought to consist primarily of periventricular leukomalacia (PVL), a distinctive form of cerebral white matter injury. Important new work shows that PVL is frequently accompanied by neuronal/axonal disease, affecting the cerebral white matter, thalamus, basal ganglia, cerebral cortex, brain stem, and cerebellum. This constellation of PVL and neuronal/axonal disease is sufficiently distinctive to be termed "encephalopathy of prematurity". The thesis of this Review is that the encephalopathy of prematurity is a complex amalgam of primary destructive disease and secondary maturational and trophic disturbances. This Review integrates the fascinating confluence of new insights into both brain injury and brain development during the human premature period.

Retardation in somatosensory cortex development induced by postnatal BrdU treatment in mice

Cerebral dysgeneses are in the background of several neurological and mental disturbances. The aim of the present study was to investigate structural and activity changes following disturbed postnatal neuronal development in mice. Newborn C57Bl6 mice were exposed to 5-bromo-2'-deoxyuridine (BrdU: daily 50 microg/g body weight) during a period between postnatal days P0-P5 or P0-P11, respectively, and neuronal malformation and malfunctioning of somatosensory (barrel field) cortex was analyzed in adolescent animals. Alterations in histological architecture of interneuronal and glial elements were studied and correlated with electrophysiological modifications. Between P30 and P35 days litters underwent ex vivo electrophysiological experiments to examine the changes in basic excitability and in synaptic efficacy. Parallel immunohistochemistry was performed to detect BrdU, GABA and GFAP. There were no BrdU immunopositive cell nuclei in control animals, but marked staining was observed in both BrdU treated groups. Lessening in the number of GABAergic neurons was observed in the treated groups. GFAP immunohistochemical analysis has shown an increased number of activated astroglial cells in treated animals. Reduction of the number of GABAergic neurons was observed in the treated groups. Electrophysiological recordings on cortical slices showed increased excitability in the treated groups.

Group I metabotropic glutamate receptors control proliferation, survival and differentiation of cultured neural progenitor cells isolated from the subventricular zone of adult mice

Neural progenitor cells (NPCs) are found in the subventricular zone (SVZ) of the adult brain, a specialized neurogenic niche that might provide a substrate for brain repair after injury. The incomplete knowledge of how NPCs in the niche respond to local signals limits the use of cultured NPCs in the development of cell transplantation strategies. We show that neurospheres obtained from the SVZ of the adult mouse expressed functional mGlu1 and mGlu5 metabotropic glutamate receptors. Pharmacological blockade of mGlu5 receptors promoted the apoptotic death of progenitors undergoing differentiation into neurons (PSA/NCAM+ cells for the most part), whereas blockade of mGlu1 receptors reduced the proliferation rate of NPCs, and promoted their differentiation towards the neuronal lineage. We conclude that endogenous activation of mGlu5 receptors might support specifically the survival of neuronal-restricted precursors, whereas endogenous activation of mGlu1 receptors might sustain the proliferation of earlier progenitors. Moreover, mGlu1 receptor antagonists increased the survival of NPCs, suggesting that endogenously activated mGlu1 receptors might play a role in the natural cell loss regulating the number or the type of progenitors.

The R246S hot-spot p53 mutant exerts dominant-negative effects in embryonic stem cells in vitro and in vivo

p53 is the most frequently mutated tumour-suppressor gene in human cancers. Mutant p53 is thought to contribute to carcinogenesis by the acquisition of gain-of-function properties or through the exertion of dominant-negative (DN) effects over the remaining wild-type protein. However, the context in which the DN effects are observed is not well understood. We have therefore generated `knock-in' mouse embryonic stem (ES) cells to investigate the effects of expressing a commonly found hot-spot p53 mutant, R246S – the mouse equivalent of human R249S, which is associated with hepatocellular carcinomas. We demonstrate here that R246S mutant p53 exhibits DN effects with respect to target gene expression, cell survival and cell cycle arrest both in cells that are in the undifferentiated state and upon differentiation. The knock-in cells contain higher levels of p53 that localizes to the nucleus even in the absence of genotoxic stress and yet remains non-functional, reminiscent of mutant p53 found in human tumours. In a model based on carbon-tetrachloride-induced liver injury, these cells were consistently highly tumorigenic in vivo, similar to p53–/– cells and in contrast to both p53+/+ and p53+/– ES cells. These data therefore indicate that the DN effects of mutant p53 are evident in the stem-cell context, in which its expression is relatively high compared with terminally differentiated cells.

Development of the human cerebral cortex: Boulder Committee revisited

In 1970 the Boulder Committee described the basic principles of the development of the CNS, derived from observations on the human embryonic cerebrum. Since then, numerous studies have significantly advanced our knowledge of the timing, sequence and complexity of developmental events, and revealed important inter-species differences. We review current data on the development of the human cerebral cortex and update the classical model of how the structure that makes us human is formed.

CNS progenitor cells and oligodendrocytes are targets of chemotherapeutic agents in vitro and in vivo

Background

Chemotherapy in cancer patients can be associated with serious short- and long-term adverse neurological effects, such as leukoencephalopathy and cognitive impairment, even when therapy is delivered systemically. The underlying cellular basis for these adverse effects is poorly understood.

Results

We found that three mainstream chemotherapeutic agents – carmustine (BCNU), cisplatin, and cytosine arabinoside (cytarabine), representing two DNA cross-linking agents and an antimetabolite, respectively – applied at clinically relevant exposure levels to cultured cells are more toxic for the progenitor cells of the CNS and for nondividing oligodendrocytes than they are for multiple cancer cell lines. Enhancement of cell death and suppression of cell division were seen in vitro and in vivo. When administered systemically in mice, these chemotherapeutic agents were associated with increased cell death and decreased cell division in the subventricular zone, in the dentate gyrus of the hippocampus and in the corpus callosum of the CNS. In some cases, cell division was reduced, and cell death increased, for weeks after drug administration ended.

Conclusion

Identifying neural populations at risk during any cancer treatment is of great importance in developing means of reducing neurotoxicity and preserving quality of life in long-term survivors. Thus, as well as providing possible explanations for the adverse neurological effects of systemic chemotherapy, the strong correlations between our in vitro and in vivo analyses indicate that the same approaches we used to identify the reported toxicities can also provide rapid in vitro screens for analyzing new therapies and discovering means of achieving selective protection or targeted killing.

Decreased neuronal nitric oxide synthase expression and cell migration in the peri-infarction after focal cerebral ischemia in rats

Neuronal nitric oxide synthase (nNOS) regulates neurogenesis in the normal developing brain, but the role of nNOS in neurogenesis of the adult ischemic brain remains unclear. The aim of this study was to investigate the temporal and spatial relationship between cell migration from the ependymal/subventricular zone (SVZ) to periinfarction and nNOS expression in the rat. Ependymal/subventricular zone cells were prelabeled with fluorescence dye DiI. Focal cerebral ischemia was induced by occlusion of the left middle cerebral artery. At 1, 3, 7, 14 and 21 days after ischemia, the rats were killed in order to determine the number of migrating cells, the colocalization of DiI and nNOS as well as nNOS quantity in specific regions. Compared to non-ischemic control and 1 day post-ischemia, the number of DiI-labeled cells in the selected regions increased at 3 days and peaked 14 days following ischemia. During 3-7 days post-ischemia, none of the migrating cells expressed nNOS and decreased nNOS expression was observed in the regions where migrating cells passed through. These results suggest the possible association between ependymal/SVZ cell migration and decreased nNOS expression within the areas including the migrating routes towards the peri-infarction.

The ectonucleotidases alkaline phosphatase and nucleoside triphosphate diphosphohydrolase 2 are associated with subsets of progenitor cell populations in the mouse embryonic, postnatal and adult neurogenic zones

Subventricular zone (SVZ)-derived adult neurospheres express two ectonucleotidases, nucleoside triphosphate diphosphohydrolase 2 (NTPDase2) and tissue non-specific alkaline phosphatase (TNAP). Agonists of the nucleotide receptors P2Y(1) and P2Y(2) as well as adenosine augment growth factor-mediated progenitor cell proliferation. NTPDase2 converts ATP and UTP to ADP and UDP, respectively, which are all P2Y receptor agonists. TNAP hydrolyzes nucleoside triphosphates and diphosphates and produces the P1 receptor agonist adenosine. In the SVZ, NTPDase2 is specifically expressed by type B cells. In order to further scrutinize the association of key molecules of the purinergic signaling pathway with neurogenic regions, we analyzed the expression of TNAP at the lateral ventricles of the adult and developing mouse brain. In the adult brain, TNAP was expressed by type B, type A and at least subsets of type C cells of the SVZ and throughout the rostral migratory stream. Almost 100% of the proliferating, Ki-67-positive cells of the adult SVZ stained for TNAP, supporting the notion of a ubiquitous association of TNAP with SVZ progenitors. In contrast, NTPDase2-positive progenitors of the dentate gyrus were TNAP-negative. Essentially all cells of the telencephalic vesicle at embryonic day (E) 14 revealed TNAP activity, including doublecortin-positive neuroblasts. During further embryonic development, enhanced TNAP activity became restricted to cells of the ventricular and SVZ. In contrast to TNAP, NTPDase2 was first expressed in the SVZ perinatally, in association with TNAP-positive SVZ border cells. During later development, NTPDase2-positive cells disappeared from the ventricular surface and began to form sheaths around clusters of subventricular doublecortin-positive cells, apparently transforming into type B cells. Our results identify TNAP and NTPDase2 as novel markers for subsets of progenitors in the adult and developing mouse brain. They further support the notion that signaling via extracellular nucleotides and nucleosides contributes to embryonic and adult neurogenesis.

Bilateral changes after neonatal ischemia in the P7 rat brain

Neurogenesis persists throughout life in the rodent subventricular zone (SVZ) and subgranular zone (SGZ) and increases in the adult after brain injury. In this study, postnatal day 7 rats underwent middle cerebral artery electrocoagulation and transient homolateral common carotid artery occlusion, a lesioning protocol that resulted in ipsilateral (IL) forebrain ischemic injury, leading to a cortical cavity 3 weeks later. The effects of neonatal ischemia on hemispheric damage, cell death, cell proliferation, and neurogenesis were examined 4 hours to 6 weeks later by the terminal deoxynucleotidyl transferase dUTP nick-end labeling assay and immunohistochemistry of Ki-67 in proliferating cells and of doublecortin, a microtubule-associated protein expressed only by immature neurons. Neonatal ischemic injury resulted in persistent reduced IL and transient reduced contralateral (CL) hemispheric areas, a consequence of sustained and transient cell death in the IL and CL areas, respectively. Ki-67 immunostaining revealed 3 peaks of newly generated cells in the dorsal SVZ and SGZ in the IL side and also in the CL side at 48 hours and 7 and 28 days after ischemia. Double immunofluorescence revealed that most of the Ki-67-positive cells were astrocytes at 48 hours. Ischemic injury also stimulated SVZ neurogenesis, based on increased doublecortin immunostaining in both SVZs at 7 to 14 days after injury. Doublecortin-positive neurons remained visible around the lesion at 21 days but displayed an immature shape in discrete chains or clusters. Although unilateral ischemic damage was produced, results indicate successful regenerative changes in the CL hemisphere, allowing anatomical recovery.

Validating in utero electroporation for the rapid analysis of gene regulatory elements in the murine telencephalon

With the ultimate goal of understanding how genetic modules have evolved in the telencephalon, we set out to modernize the functional analysis of cross-species cis-regulatory elements in mouse. In utero electroporation is rapidly replacing transgenesis as the method of choice for gain- and loss-of-function studies in the murine telencephalon, but the application of this technique to the analysis of transcriptional regulation has yet to be fully explored and exploited. To empirically define the developmental stages required to target specific populations of neurons in the dorsal telencephalon, or pallium, which gives rise to the neocortex in mouse, we performed a temporal and spatial analysis of the migratory properties of electroporated versus birth-dated cells. Next, we compared the activities of two known Ngn2 enhancers via transgenesis and in utero electroporation, demonstrating that the latter technique more faithfully reports the endogenous telencephalic expression pattern observed in an Ngn2lacZ knock-in line. Finally, we used this approach to test the telencephalic activities of a series of deletion constructs comprised of the zebrafish ER81 upstream regulatory region, allowing us to identify a previously uncharacterized enhancer that displays cross-species activity in the murine piriform cortex and lateral neocortex, yet not in more medial domains of the forebrain. Taken together, our data supports the contention that in utero technology can be exploited to rapidly examine the architecture and evolution of pallial-specific cis-regulatory elements.

Developmental ability of cloned embryos from neural stem cells

The success rate is generally higher when cloning mice from embryonic stem (ES) cell nuclei than from somatic cell nuclei, suggesting that the embryonic nature or the undifferentiated state of the donor cell increases cloning efficiency. We assessed the developmental ability of cloned embryos derived from cultured neural stem cell (NSC) nuclei and compared the success rate with that of embryos cloned from other donor cells such as differentiated NSCs, cumulus cells, Sertoli cells and ES cells in the mouse. The transfer of two-cell cloned embryos derived from cultured NSC nuclei into surrogate mothers produced five live cloned mice. However, the success rate (0.5%) was higher in embryos cloned from cultured NSC nuclei than from differentiated NSCs (0%), but lower than that obtained by cloning mice from other cell nuclei (2.2-3.5%). Although the in vitro developmental potential to the two-cell stage of the cloned embryos derived from NSC nuclei (73%) was similar to that of the cloned embryos derived from other somatic cell nuclei (e.g., 85% in Sertoli cells and 75% in cumulus cells), the developmental rate to the morula-blastocyst stage was only 7%. This rate is remarkably lower than that produced from other somatic cells (e.g., 50% in Sertoli cells and 54% in cumulus cells). These results indicate that the undifferentiated state of neural cells does not enhance the cloning efficiency in mice and that the arrest point for in vitro development of cloned embryos depends on the donor cell type.

Oxygen tension regulates survival and fate of mouse central nervous system precursors at multiple levels

Despite evidence that oxygen regulates neural precursor fate, the effects of changing oxygen tensions on distinct stages in precursor differentiation are poorly understood. We found that 5% oxygen permitted clonal and long-term expansion of mouse fetal cortical precursors. In contrast, 20% oxygen caused a rapid decrease in hypoxia-inducible factor 1alpha and nucleophosmin, followed by the induction of p53 and apoptosis of cells. This led to a decrease in overall cell number and particularly a loss of astrocytes and oligodendrocytes. Clonal analysis revealed that apoptosis in 20% oxygen was due to a complete loss of CD133(lo)CD24(lo) multipotent precursors, a substantial loss of CD133(hi)CD24(lo) multipotent precursors, and a failure of remaining CD133(hi)CD24(lo) cells to generate glia. In contrast, committed neuronal progenitors were not significantly affected. Switching clones from 5% to 20% oxygen only after mitogen withdrawal led to a decrease in total clone numbers but an even greater decrease in oligodendrocyte-containing clones. During this late exposure to 20% oxygen, bipotent glial (A2B5+) and early (platelet-derived growth factor receptor alpha) oligodendrocyte progenitors appeared and disappeared more quickly, relative to 5% oxygen, and late stage O4+ oligodendrocyte progenitors never appeared. These results indicate that multipotent cells and oligodendrocyte progenitors are more susceptible to apoptosis at 20% oxygen than committed neuronal progenitors. This has important implications for optimizing ex vivo production methods for cell replacement therapies.

Perlecan controls neurogenesis in the developing telencephalon

Background

Perlecan is a proteoglycan expressed in the basal lamina of the neuroepithelium during development. Perlecan absence does not impair basal lamina assembly, although in the 55% of the mutants early disruptions of this lamina conducts to exencephaly, impairing brain development. The rest of perlecan-null brains complete its prenatal development, maintain basal lamina continuity interrupted by some isolated ectopias, and are microcephalic. Microcephaly consists of thinner cerebral walls and underdeveloped ganglionic eminences. We have studied the mechanisms that generate brain atrophy in telencephalic areas where basal lamina is intact.

Results

Brain atrophy in the absence of perlecan started in the ventral forebrain and extended to lateral and dorsal parts of the cortex in the following stages. First, the subpallial forebrain developed poorly in early perlecan-null embryos, because of a reduced cell proliferation: the number of cells in mitosis decreased since the early stages of development. This reduction resulted in a decreased tangential migration of interneurons to the cerebral cortex. Concomitant with the early hypoplasia observed in the medial ganglionic eminences, Sonic Hedgehog signal decreased in the perlecan-null floor plate basal lamina at E12.5. Second, neurogenesis in the pallial neuroepithelium was affected in perlecan deficient embryos. We found reductions of nearly 50% in the number of cells exiting the cell cycle at E12–E13. The labeling index, which was normal at this age, significantly decreased with advancing corticogenesis. Moreover, nestin⁺ or PCNA⁺ progenitors increased since E14.5, reaching up to about 150% of the proportion of PCNA⁺ cells in the wild-type at E17.5. Thus, labeling index reduction together with increased progenitor population, suggests that atrophy is the result of altered cell cycle progression in the cortical progenitors. Accordingly, less neurons populated the cortical plate and subplate of perlecan-null neocortex, as seen with the neuronal markers β-tubulin and Tbr1.

Conclusion

As a component of the basal lamina, perlecan both maintains this structure and controls the response of the neuroepithelium to growth factors. Less mitotic cells in the early medial ganglionic eminences, and impaired cell cycle progression in the late neocortex, suggests insufficient recruitment and signaling by neurogenic morphogens, such as SHH or FGF2.

Developmental changes and injury induced disruption of the radial organization of the cortex in the immature rat brain revealed by in vivo diffusion tensor MRI

During brain development, morphological changes modify the cortex from its immature radial organization to its mature laminar appearance. Applying in vivo diffusion tensor imaging (DTI), the microstructural organization of the cortex in the immature rat was analyzed and correlated to neurohistopathology. Significant differences in apparent diffusion coefficient (ADC) and fractional anisotropy (FA) were detected between the external (I-III) and deep (IV-VI) cortical layers in postnatal day 3 (P3) and P6 pups. With cortical maturation, ADC was reduced in both cortical regions, whereas a decrease in FA was only seen in the deep layers. A distinct radial organization of the external cortical layers with the eigenvectors perpendicular to the pial surface was observed at both ages. Histology revealed maturational differences in the cortical architecture with increased neurodendritic density and reduction in the radial glia scaffolding. Early DTI after hypoxia-ischemia at P3 shows reduced ADC and FA in the ipsilateral cortex that persisted at P6. Cortical DTI eigenvector maps reveal microstructural disruption of the radial organization corresponding to regions of neuronal death, radial glial disruption, and astrocytosis. Thus, the combined use of in vivo DTI and histopathology can assist in delineating normal developmental changes and postinjury modifications in the immature rodent brain.

Neural stem/progenitor cells participate in the regenerative response to perinatal hypoxia/ischemia

Perinatal hypoxia/ischemia (H/I) is the leading cause of neurologic injury resulting from birth complications. Recent advances in critical care have dramatically improved the survival rate of infants suffering this insult, but approximately 50% of survivors will develop neurologic sequelae such as cerebral palsy, epilepsy or cognitive deficits. Here we demonstrate that tripotential neural stem/progenitor cells (NSPs) participate in the regenerative response to perinatal H/I as their numbers increase 100% by 3 d and that they alter their intrinsic properties to divide using expansive symmetrical cell divisions. We further show that production of new striatal neurons follows the expansion of NSPs. Increased proliferation within the NSP niche occurs at 2 d after perinatal H/I, and the proliferating cells express nestin. Of those stem-cell related genes that change, the membrane receptors Notch1, gp-130, and the epidermal growth factor receptor, as well as the downstream transcription factor Hes5, which stimulate NSP proliferation and regulate stem cellness are induced before NSP expansion. The mechanisms for the reactive expansion of the NSPs reported here reveal potential therapeutic targets that could be exploited to amplify this response, thus enabling endogenous precursors to restore a normal pattern of brain development after perinatal H/I.

Hypoxia/ischemia expands the regenerative capacity of progenitors in the perinatal subventricular zone

Neurons and oligodendrocyte progenitors are highly sensitive to perinatal hypoxic-ischemic injury. As accumulating evidence suggests that many insults to the human infant occur in utero, and preventing brain damage to infants in utero will prove difficult, there is strong rationale to pursue regenerative strategies to reduce the morbidity associated with developmental brain injuries. The purpose of this study was to determine whether a hypoxic-ischemic insult stimulates the neural stem/progenitor cells in the subventricular zone to generate new neurons and oligodendrocytes. Hypoxia-ischemia was induced using the Vannucci rat model on postnatal day-6 pups. Injections of 5'-bromo-2'-deoxyuridine to label cells undergoing DNA synthesis after hypoxia-ischemia revealed that there is a robust proliferative response within the subventricular zone of the injured hemisphere that continues for at least 1 week after the hypoxic-ischemic episode. Using the neurosphere assay to quantify the number of neural stem/progenitor cells in the subventricular zone, we find that there are twice as many neural stem/progenitor cells in the affected dorsolateral subventricular zone at 1 week of recovery and that these cells generate larger spheres in response to growth factors compared with controls. Precursors from the injured hemisphere generate three times as many neurons in vitro and more than twice as many oligodendroglia compared with controls. Hypoxia-ischemia also increases neurogenesis in vivo. Doublecortin positive cells with migratory profiles were observed streaming from the ipsilateral subventricular zone to the striatum and neocortex, whereas, few doublecortin positive cells were found in the contralateral hemisphere after hypoxia-ischemia. These observations provide evidence that the somatic neural progenitors of the subventricular zone participate in the production of new brain cells lost after hypoxia-ischemia.

MRI of normal fetal brain development

Normal fetal brain maturation can be studied by in vivo magnetic resonance imaging (MRI) from the 18th gestational week (GW) to term, and relies primarily on T2-weighted and diffusion-weighted (DW) sequences. These maturational changes must be interpreted with a knowledge of the histological background and the temporal course of the respective developmental steps. In addition, MR presentation of developing and transient structures must be considered. Signal changes associated with maturational processes can mainly be ascribed to the following changes in tissue composition and organization, which occur at the histological level: (1) a decrease in water content and increasing cell-density can be recognized as a shortening of T1- and T2-relaxation times, leading to increased T1-weighted and decreased T2-weighted intensity, respectively; (2) the arrangement of microanatomical structures to create a symmetrical or asymmetrical environment, leading to structural differences that may be demonstrated by DW-anisotropy; (3) changes in non-structural qualities, such as the onset of a membrane potential in premyelinating axons. The latter process also influences the appearance of a structure on DW sequences. Thus, we will review the in vivo MR appearance of different maturational states of the fetal brain and relate these maturational states to anatomical, histological, and in vitro MRI data. Then, the development of the cerebral cortex, white matter, temporal lobe, and cerebellum will be reviewed, and the MR appearance of transient structures of the fetal brain will be shown. Emphasis will be placed on the appearance of the different structures with the various sequences. In addition, the possible utility of dynamic fetal sequences in assessing spontaneous fetal movements is discussed.

Treatment with olanzapine increases cell proliferation in the subventricular zone and prefrontal cortex

The present study examines the effect of chronic treatment with two atypical neuroleptics, commonly used to treat schizophrenia. Adult rats were given either risperidone or olanzapine in their drinking water for 21 days. Memory was assessed on the first and last day of treatment using an object discrimination test, and the rate of cell proliferation in the subventricular zone (SVZ), dentate gyrus (DG) and prefrontal cortex (PFC) was quantified by immuno staining for Ki-67. The results show that both risperidone and olanzapine significantly improved performance in object discrimination after 21 days, and additionally, olanzapine significantly increased cell proliferation in the SVZ and PFC but not the DG.

In vivo Evidence for Radial Migration of Neurons by Long-Distance Somal Translocation in the Developing Ferret Visual Cortex

During the development of the cerebral cortex, neurons generated in the cortical ventricular zone migrate radially toward the marginal zone. Radially migrating neurons are thought to display 1 of 2 morphologies: cells with a long, pia-contacting, apical process utilized for somal translocation early in development, when the cortex is still relatively thin; or cells with a short leading process, abundant at late stages of corticogenesis when neurons need to travel for longer distances. In large convoluted brains, like those of many primates and carnivores, radially migrating neurons must travel distances up to several millimeters before reaching their final destination, often following curvilinear trajectories. Here we analyze modes and morphologies of radially migrating neurons in convoluted brains by studying the visual cortex of developing ferrets. We provide in vivo and in vitro evidence for the existence of late-born cortical neurons that migrate radially by long-distance somal translocation within a long apical process extended to the cortical plate, in contrast to the early somal translocation observed in rodents. Long-distance translocating neurons in the ferret show a discontinuous rhythm of migration, alternating periods of advance with periods of stall. Furthermore, by combining different labeling methods we find the simultaneous presence in the developing ferret cortex of long-distance translocating neurons and neurons migrating within a short leading process.

An evolutionary perspective on FoxP2: strictly for the birds?

FoxP2 mutations in humans are associated with a disorder that affects both the comprehension of language and its production, speech. This discovery provided the first opportunity to analyze the genetics of language with molecular and neurobiological tools. The amino acid sequence and the neural expression pattern of FoxP2 are extremely conserved, from reptile to man. This suggests an important role for FoxP2 in vertebrate brains, regardless of whether they support imitative vocal learning or not. Its expression pattern pinpoints neural circuits that might have been crucial for the evolution of speech and language, including the basal ganglia and the cerebellum. Recent studies in songbirds show that during times of song plasticity FoxP2 is upregulated in a striatal region essential for song learning. This suggests that FoxP2 plays important roles both in the development of neural circuits and in the postnatal behaviors they mediate.

Progenitor cells from the adult mouse brain acquire a neuronal phenotype in response to beta-amyloid

Neurospheres from adult mouse subventricular zone (SVZ) were grown in suspension cultures for 12-15 days. Neurospheres consisted mainly of neural precursor cells (NPCs) immunoreactive for nestin and also contained nestin-negative precursors. We used these neurospheres to determine the effects of synthetic beta-amyloid fragments (both betaAP(1-42) and betaAP(25-35)) on NPC proliferation, differentiation and survival. We show that neurospheres exposed to 25 microM betaAP(25-35) or betaAP(1-42) for 24 h (a toxic condition for mature neurons) did not undergo apoptosis. Instead, betaAP(25-35) orientated nestin-negative precursors towards nestin-positive NPCs and turned nestin-positive NPCs into neuroblasts. Intracerebroventricular infusion of full-length betaAP(1-42) increased the population of PSA-NCAM-positive cells in the SVZ, without affecting proliferation. We conclude that betaAP influences the fate of progenitor cells, driving their differentiation towards a neuronal lineage.

Neuronal migration in the murine rostral migratory stream requires serum response factor

The central nervous system is fundamentally dependent on guided cell migration, both during development and in adulthood. We report an absolute requirement of the transcription factor serum response factor (SRF) for neuronal migration in the mouse forebrain. Conditional, late-prenatal deletion of Srf causes neurons to accumulate ectopically at the subventricular zone (SVZ), a prime neurogenic region in the brain. SRF-deficient cells of the SVZ exhibit impaired tangential chain migration along the rostral migratory stream into the olfactory bulb. SVZ explants display retarded chain migration in vitro. Regarding target genes, SRF deficiency impairs expression of the beta-actin and gelsolin genes, accompanied by reduced cytoskeletal actin fiber density. At the posttranslational level, cofilin, a key regulator of actin dynamics, displays dramatically elevated inhibitory phosphorylation at Ser-3. Our studies indicate that SRF-controlled gene expression directs both the structure and dynamics of the actin microfilament, thereby determining cell-autonomous neuronal migration.

Differentiation prevents assessment of neural stem cell pluripotency after blastocyst injection

Earlier studies reported that neural stem (NS) cells injected into blastocysts appeared to be pluripotent, differentiating into cells of all three germ layers. In this study, we followed in vitro green fluorescent protein (GFP)-labeled NS and embryonic stem (ES) cells injected into blastocysts. Forty-eight hours after injection, significantly fewer blastocysts contained GFP-NS cells than GFP-ES cells. By 96 hours, very few GFP-NS cells remained in blastocysts compared with ES cells. Moreover, 48 hours after injection, GFP-NS cells in blastocysts extended long cellular processes, ceased expressing the NS cell marker nestin, and instead expressed the astrocytic marker glial fibrillary acidic protein. GFP-ES cells in blastocysts remained morphologically undifferentiated, continuing to express the pluripotent marker stage-specific embryonic antigen-1. Selecting cells from the NS cell population that preferentially formed neurospheres for injection into blastocysts resulted in identical results. Consistent with this in vitro behavior, none of almost 80 mice resulting from NS cell-injected blastocysts replaced into recipient mothers were chimeric. These results strongly support the idea that NS cells cannot participate in chimera formation because of their rapid differentiation into glia-like cells. Thus, these results raise doubts concerning the pluripotency properties of NS cells.

Isolation of immortalized, INK4a/ARF-deficient cells from the subventricular zone after in utero N-ethyl-N-nitrosourea exposure

OBJECT

Brain tumors, including gliomas, develop several months after rats are exposed in utero to N-ethyl-N-nitroso-urea (ENU). Although pathological changes cannot be detected until these animals are several weeks old, the process that eventually leads to glioma formation must begin soon after exposure given the rapid clearance of the carcinogen and the observation that transformation of brain cells isolated soon after exposure occasionally occurs. This model can therefore potentially provide useful insights about the early events that precede overt glioma formation. The authors hypothesized that future glioma cells arise from stem/progenitor cells residing in or near the subventricular zone (SVZ) of the brain.

METHODS

Cells obtained from the SVZ or corpus striatum in ENU-exposed and control rats were cultured in an epidermal growth factor (EGF)-containing, chemically defined medium. Usually, rat SVZ cells cultured in this manner (neurospheres) are nestin-positive, undifferentiated, and EGF-dependent and undergo cell senescence. Consistent with these prior observations, control SVZ cells undergo senescence by the 12th to 15th doubling (20 of 20 cultures). In contrast, three of 15 cultures of cells derived from the SVZs of individual ENU-treated rats continue to proliferate for more than 60 cell passages. Each of these nestin-expressing immortalized cell lines harbored a common homozygous deletion spanning the INK4a/ARF locus and was unable to differentiate into neural lineages after exposure to specific in vitro stimuli. Nevertheless, unlike the rat C6 glioma cell line, these immortalized cell lines demonstrate EGF dependence and low clonogenicity in soft agar and did not form tumors after intracranial transplantation.

CONCLUSIONS

Data in this study indicated that immortalized cells may represent glioma precursors that reside in the area of the SVZ after ENU exposure that may serve as a reservoir for further genetic and epigenetic hits that could eventually result in a full glioma phenotype.

Development of GABAergic neurons from the ventricular zone in the superior colliculus of the mouse

The superior colliculus (SC) is a layered structure in the midbrain and is particularly rich in gamma-aminobutyric acid (GABA). The present investigation aimed to determine whether the development of GABAergic neurons in the SC is common to that of the neocortex in which they are produced in a distinct area called the ganglionic eminence and are transported by tangential migration. A green fluorescent protein (GFP) knock-in mouse was used in which a GFP gene was introduced into the gene for glutamic acid decarboxylase (GAD) 67 and all GABAergic neurons were fluorescent. At embryonic day (E) 11-14, GFP-positive cells increased strikingly. They were spindle-shaped with processes at both poles and oriented radially between the ventricular and pial surface, together with other GFP-negative cells. After the cutting of the embryonic SC, GFP-positive cells accumulated on one side of the injury as expected from their radial but not tangential migration. In the living slice preparations GFP-positive cells migrated radially during the observation. These results indicate that tangential migration of GABAergic neurons as observed in the neocortex is not applicable and that radial migration from the underlying ventricular zone is predominant in the SC. At E12-13, bundles of commissural GFP-positive fibers which appeared to originate outside the SC were distributed at the superficial layer. These superficial fibers were no longer observed at the later stages.

CNTF/LIF/gp130 receptor complex signaling maintains a VZ precursor differentiation gradient in the developing ventral forebrain

The extrinsic signaling pathways responsible for the formation and maintenance of the unique laminar organization of the forebrain germinal zones are largely unknown. In the present study, we asked whether ciliary neurotrophic factor (CNTF)/leukemia inhibitory factor (LIF)/gp130 signaling plays a role in the development of the germinal layers in the lateral ganglionic eminence. We found that CNTF/LIF/gp130 receptor signaling promotes the self-renewal/expansion of a subpopulation of fibroblast growth factor-responsive ventricular zone (VZ) precursors in the ventral forebrain. Analysis of Lifr-/- mice suggests that CNTF/LIF/gp130 signaling maintains a subpopulation of GSH2+ VZ precursors, which are necessary for normal growth of the early ventral forebrain and for maintaining a gradient of VZ precursor differentiation in the lateral ganglionic eminence, as defined by GSH2, MASH1 and DLX2 expression. Furthermore, addition of exogenous CNTF to embryonic forebrain explant cultures deprived of choroid plexus-derived CNTF, was sufficient to promote a VZ differentiation gradient. In contrast to the forebrain, CNTF/LIF/gp130 signaling reduced, rather than enhanced, precursor self-renewal/expansion in the spinal cord. These results demonstrate a novel region-specific role for CNTF/LIF/gp130 signaling in the development of the germinal layers of the embryonic telencephalon.