Localization of transitin mRNA, a nestin-like intermediate filament family member, in chicken radial glia processes

Neurotrophic Factor-α1: A Key Wnt-β-Catenin Dependent Anti-Proliferation Factor and ERK-Sox9 Activated Inducer of Embryonic Neural Stem Cell Differentiation to Astrocytes in Neurodevelopment

Embryonic neurodevelopment involves inhibition of proliferation of multipotent neural stem cells (NSCs) followed by differentiation into neurons, astrocytes and oligodendrocytes to form the brain. We have identified a new neurotrophic factor, NF-α1, which inhibits proliferation and promotes differentiation of NSC/progenitors derived from E13.5 mouse cortex. Inhibition of proliferation of these cells was mediated through negatively regulating the Wnt pathway and decreasing β-catenin. NF-α1 induced differentiation of NSCs to astrocytes by enhancing Glial Fibrillary Acidic Protein (GFAP) expression through activating the ERK1/2-Sox9 signaling pathway. Cultured E13.5 cortical stem cells from NF-α1-knockout mice showed decreased astrocyte numbers compared to wild-type mice, which was rescued by treatment with NF-α1. In vivo, immunocytochemistry of brain sections and Western blot analysis of neocortex of mice showed a gradual increase of NF-α1 expression from E14.5 to P1 and a surge of GFAP expression at P1, the time of increase in astrogenesis. Importantly, NF-α1-Knockout mice showed ∼49% fewer GFAP positive astrocytes in the neocortex compared to WT mice at P1. Thus, NF-α1 is critical for regulating antiproliferation and cell fate determination, through differentiating embryonic stem cells to GFAP-positive astrocytes for normal neurodevelopment. Stem Cells 2017;35:557-571.

Tangential migration of glutamatergic neurons and cortical patterning during development: Lessons from Cajal-Retzius cells

Tangential migration is a mode of cell movement, which in the developing cerebral cortex, is defined by displacement parallel to the ventricular surface and orthogonal to the radial glial fibers. This mode of long-range migration is a strategy by which distinct neuronal classes generated from spatially and molecularly distinct origins can integrate to form appropriate neural circuits within the cortical plate. While it was previously believed that only GABAergic cortical interneurons migrate tangentially from their origins in the subpallial ganglionic eminences to integrate in the cortical plate, it is now known that transient populations of glutamatergic neurons also adopt this mode of migration. These include Cajal-Retzius cells (CRs), subplate neurons (SPs), and cortical plate transient neurons (CPTs), which have crucial roles in orchestrating the radial and tangential development of the embryonic cerebral cortex in a noncell-autonomous manner. While CRs have been extensively studied, it is only in the last decade that the molecular mechanisms governing their tangential migration have begun to be elucidated. To date, the mechanisms of SPs and CPTs tangential migration remain unknown. We therefore review the known signaling pathways, which regulate parameters of CRs migration including their motility, contact-redistribution and adhesion to the pial surface, and discuss this in the context of how CR migration may regulate their signaling activity in a spatial and temporal manner. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 847-881, 2016.

Radial glia regulate Cajal-Retzius cell positioning in the early embryonic cerebral cortex

The organization of neocortex, along its radial axis, into a six-layered structure is one of the most exquisite features of the brain. Because of their strategic localization in the marginal zone, and their expression of reelin, a signal that controls spatial ordering of cortical layers, Cajal-Retzius (C-R) cells play a crucial role in cortical patterning along this axis. Yet, it remains less well understood how C-R cell targeting itself is regulated. At the onset of corticogenesis when C-R cells first arrive in the cortex via tangential migration, radial glia (RG) are the main cell type present. This suggests that RG may play a role in C-R cell localization. To test this, we used genetic approaches to perturb RG scaffold during early corticogenesis. We found that disrupting RG endfoot adhesion to basal lamina consistently results in C-R cell displacement. These displacements do not appear to result from primary defects in neural progenitor cell proliferation, deficits in the meninges or basement membrane, or cell autonomous defects in C-R cells. Instead, they show close temporal and spatial correlation with RG endfoot retraction. Moreover, ablation of RG via cell cycle blockade similarly results in local displacement of C-R cells. These lines of evidence thus indicate that, during early corticogenesis, RG play a primary role in regulating spatial targeting of C-R cells. Since RG are also neural progenitors as well as neuronal migration scaffolds, these findings suggest that, during nervous system development, neuroepithelial stem cells may not only be responsible for generating a diverse array of neuronal cell types and facilitating their radial migration. They may also, through regulating the placement of guidepost cells, coordinate spatial patterning of the nervous system along its radial axis.

Characterization of neural stem/progenitor cells expressing VEGF and its receptors in the subventricular zone of newborn piglet brain

Neural stem/progenitor cell (NSP) biology and neurogenesis in adult central nervous system (CNS) are important both towards potential future therapeutic applications for CNS repair, and for the fundamental function of the CNS. In the present study, we report the characterization of NSP population from subventricular zone (SVZ) of neonatal piglet brain using in vivo and in vitro systems. We show that the nestin and vimentin-positive neural progenitor cells are present in the SVZ of the lateral ventricles of neonatal piglet brain. In vitro, piglet NSPs proliferated as neurospheres, expressed the typical protein of neural progenitors, nestin and a range of well-established neurodevelopmental markers. Upon dissociation and subculture, piglet NSPs differentiated into neurons and glial cells. Clonal analysis demonstrates that piglet NSPs are multipotent and retain the capacity to generate both glia and neurons. These cells expressed VEGF, VEGFR1, VEGFR2 and Neuropilin-1 and -2 mRNAs. Real time PCR revealed that SVZ NSPs from newborn piglet expressed total VEGF and all VEGF splice variants. These findings show that piglet NSPs may be helpful to more effectively design growth factor based strategies to enhance endogenous precursor cells for cell transplantation studies potentially leading to the application of this strategy in the nervous system disease and injury.

Glial migratory streams in the developing hindbrain: a slice culture approach

Compared to our knowledge of neurogenesis, relatively little is known about glial cell specification and migration during central nervous system development. We have established a novel chick hindbrain slice preparation which permits examination of gliogenesis in its native environment, providing a means to study the signaling pathways involved in glial cell specification and migration during development. Cells in the hindbrain slice preparations mature in a manner which is similar to in vivo developmental timing and patterning paradigms. To demonstrate the utility of this approach, we examined the effect of the retinoic acid signaling pathway on cells in these slices, showing that addition of exogenous trans-retinoic acid to slice cultures promotes expression of a marker of mature astrocytes, glial fibrillary acidic protein (GFAP), while the inhibition of endogenous retinoic acid synthesis reduces GFAP expression; the results suggest a role for retinoic acid in modulating glial differentiation. Using these hindbrain slice cultures, we have used two different approaches to label glial progenitors specifically at the ventricular zone and have observed for the first time the ventrally-directed migration of these cells from the ventricular zone of the hindbrain. This slice culture system is thus an innovative and robust tool for examining glial cell migration and the extracellular molecular and signaling pathways which regulate glial differentiation.

Aggrecan is expressed by embryonic brain glia and regulates astrocyte development

Determination of the molecules that regulate astrocyte development has been hindered by the paucity of markers that identify astrocytic precursors in vivo. Here we report that the chondroitin sulfate proteoglycan aggrecan both regulates astrocyte development and is expressed by embryonic glial precursors. During chick brain development, the onset of aggrecan expression precedes that of the astrocytic marker GFAP and is concomitant with detection of the early glial markers GLAST and glutamine synthetase. In co-expression studies, we established that aggrecan-rich cells contain the radial glial markers nestin, BLBP and GLAST and later in embryogenesis, the astroglial marker GFAP. Parallel in vitro studies showed that ventricular zone cultures, enriched in aggrecan-expressing cells, could be directed to a GFAP-positive fate in G5-supplemented differentiation media. Analysis of the chick aggrecan mutant nanomelia revealed marked increases in the expression of the astrocyte differentiation genes GFAP, GLAST and GS in the absence of extracellular aggrecan. These increases in astrocytic marker gene expression could not be accounted for by changes in precursor proliferation or cell death, suggesting that aggrecan regulates the rate of astrocyte differentiation. Taken together, these results indicate a major role for aggrecan in the control of glial cell maturation during brain development.

Transitin, a nestin-like intermediate filament protein, mediates cortical localization and the lateral transport of Numb in mitotic avian neuroepithelial cells

Neuroepithelium is an apicobasally polarized tissue that contains neural stem cells and gives rise to neurons and glial cells of the central nervous system. The cleavage orientation of neural stem cells is thought to be important for asymmetric segregation of fate-determinants, such as Numb. Here, we show that an intermediate filament protein, transitin, colocalizes with Numb in the cell cortex of mitotic neuroepithelial cells, and that transitin anchors Numb via a physical interaction. Detailed immunohistological and time-lapse analyses reveal that basal Numb-transitin complexes shift laterally during mitosis, allowing asymmetric segregation of Numb-transitin to one of the daughter cells, even when the cell cleavage plane is perpendicular to the ventricular surface. In addition, RNA interference (RNAi) knockdown of the transitin gene reveals its involvement in neurogenesis. These results indicate that transitin has important roles in determining the intracellular localization of Numb, which regulates neurogenesis in the developing nervous system of avian embryos.

Immunohistochemical changes related to ageing in the mouse hippocampus and subventricular zone

We investigated mainly immunohistochemical changes of nestin (a marker of neuroepithelial stem cells) and Ki-67 (a marker of proliferating cells) proteins related to ageing in the mouse hippocampus and subventricular zone (SVZ) using young adult (8 weeks old) and middle-aged (40 weeks old) mice. In the present study, no significant changes in neurons and astrocytes of the hippocampal CA1 sector were found in a middle-aged male ICR mice without severe senile weakness, as compared with young adult animals. In contrast, a significant change in the number of microglia was found in the hippocampal CA1 sector of the middle-aged mice. Furthermore, no significant changes in the number of nestin- and Ki-67-positive cells were observed in the hippocampal CA1 sector of the middle-aged mice. On the other hand, decreases in the number of nestin- and Ki-67-immunopositive cells were observed in the SVZ of the middle-aged mice. Furthermore, a migration of nestin- and Ki-67-immunoreactive cells in the corpus callosum was not observed in the SVZ of the middle-aged mice. In the dentate gyrus, significant decreases in the number of Ki-67-immunopositive cells were observed in the middle-aged mice. Our study also showed that nestin immunoreactivity was observed in both Ki-67-postive cells and astrocytes in the SVZ of young adult mice. These findings emphasize the need to recognize ageing as important factors in studies of microglia, which may help to clarify the role of glial cell structure and function during ageing processes. Furthermore, the present findings suggest that ageing processes may decrease neurogenesis in the corpus callosum, SVZ and dentate gyrus. Thus our present findings provide valuable information for the neurogenesis during ageing processes.

Intermediate filament protein synemin is present in human reactive and malignant astrocytes and associates with ruffled membranes in astrocytoma cells

Synemin, a very unique type VI intermediate filament (IF) protein, exhibits alternative splice variants termed alpha and beta. Unlike other IF proteins, synemin binds to actin-associated proteins, including alpha-actinin, vinculin, and alpha-dystrobrevin. Our previous work has demonstrated the presence of synemin in differentiating astrocytes. In this study, we have examined the presence of synemin in human astrocytes under pathological conditions, using rabbit antibodies raised against the C-terminal domain of human synemin produced in bacteria. Western blotting shows that astrocytic tumors contain greater amounts of alpha-synemin than do normal brain tissues. These tumors also contain beta-synemin, which is not detectable in normal brain. Immunohistochemistry demonstrates that, while synemin is present in normal adult brain only in vascular smooth muscle cells, it is newly synthesized by reactive and neoplastic astrocytes. Alpha- and beta-Synemins have also been detected by Western blotting and polymerase chain reaction in several human glioblastoma cell lines. In these cell lines, surprisingly, synemin is associated with ruffled membranes in addition to being distributed along the IF network. In ruffled membranes, synemin was found to co-localize with alpha-actinin. This unusual cellular localization for an IF protein is maintained after nocodazole-induced perinuclear coiling of the vimentin IF network. In addition, immunoprecipitation experiments demonstrate that synemin forms a complex with alpha-actinin in glioblastoma cells. Taken together with synemin localization within ruffled membranes, this finding suggests that synemin plays a role in motility of glioblastoma cells.

Transitin, a nestin-related intermediate filament, is expressed by neural progenitors and can be induced in Müller glia in the chicken retina

The purpose of this study was to test whether transitin, the avian homologue of nestin, is expressed by retinal progenitors in the developing and postnatal chicken. Because nestin has been widely used as a cell-distinguishing marker of neural progenitors in the mammalian nervous system, we expected to find transitin expressed specifically by the neural progenitors of the retina. In early stages of development, transitin is expressed by neural progenitors in the retina and by cells in the developing ciliary body. During later stages of development, transitin expression persists in differentiating Müller glia but is down-regulated by these cells as maturation proceeds. In the postnatal chick, transitin expression is restricted to neural progenitors at the peripheral edge of the retina. We found that the expression of transitin in mature Müller glia was induced by intraocular injections of insulin and fibroblast growth factor-2 (FGF2) but not by ciliary neurotrophic factor. In response to insulin and FGF2, the expression of transitin was induced in the nonpigmented epithelium (NPE) of the ciliary body. In the postnatal retina, acute retinal damage transiently induces transitin expression in Müller glia. We propose that the expression of transitin by retinal Müller glia and NPE cells in the postnatal animal represents a state of de-differentiation and a step toward becoming neurogenic progenitor cells. Taken together, our findings indicate that transitin is expressed by neural progenitors in the embryonic and postnatal chicken retina. However, transitin is not exclusively expressed by neural progenitors and is also expressed by non-neurogenic cells.

Identification of brain-derived neurotrophic factor in nestin-expressing astroglial cells in the neostriatum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice

Up-regulation of nestin expression was significantly induced in the caudate-putamen of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice in our previous observation [Brain Res 925 (2002) 9]. We hypothesized that the nestin-expressing cells might play an important role in the pathogenesis of parkinsonian model, and characterization of these nestin-expressing cells was studied by RT-PCR, immunohistochemistry and semi-quantitative analysis for various markers of glial fibrillary acid protein (GFAP), S-100, neuronal nuclear specific protein (NeuN), beta-tubulin, Ki-67 and brain-derived neurotrophic factor (BDNF) expression in MPTP-treated C57/BL mice. Firstly, significant increasing in both nestin protein and mRNA was found in MPTP-treated mice. Up-regulation of nestin expression started at day 1, peaked at day 3, and gradually went down at days 7-21 in the neostriatum after MPTP treatment. Secondly, double immunofluorescence indicated that almost all of nestin-positive cells exhibited GFAP (98%) or S-100 (96%)-immunoreactivity, whereas NeuN or beta-tubulin was hardly detected in these nestin-positive cells. Thirdly, a minor population (7.0%) of nestin-positive cells showed Ki-67 (cell proliferation marker)-immunoreactivity, showing some of them went into cell mitotic state. Finally but more interestingly, a major population (86%) of nestin-expressing cells also exhibited immunoreactivity for BDNF, one neurotrophic factor. These results present time-dependent up-regulation of nestin expression in neostriatum, the proliferative and neurotrophic properties of nestin-expressing astroglial cells in MPTP-treated C57/BL mice. Taken together with previous observations, this study suggests that nestin-expressing activated astroglial cells, possibly partially through synthesizing and releasing neurotrophic factors such as BDNF in the basal ganglia, may play important roles in protection of nigrostriatal dopamine neurons and in the pathogenesis of Parkinson's disease in mammals.

Nestin-containing cells express glial fibrillary acidic protein in the proliferative regions of central nervous system of postnatal developing and adult mice

We are interested in the expression patterns of nestin, an embryonic intermediate filament that represent a neural precursor marker, in the mammalian central nervous system. With an immunohistochemical approach, distribution of nestin-containing cells and their colocalization with glial fibrillary acidic protein (GFAP) or neuronal nuclear specific protein (NeuN) were studied in adult and postnatal days 2-30 (P2-30) mice. Nestin-immunoreactivity was predominately distributed in certain proliferative regions, such as cerebral cortex, hippocampus, hypothalamus, subfornical organ, cerebellar cortex, area postrema, midline raphe glial structures, as well as ependymal and subependymal zones of the brain and spinal cord. The majority of nestin-immunoreactive cells, characterized by astroglial profiles of multiple and radial processes, showed a partial overlapping distribution with that of GFAP-immunoreactive astroglial cells. Double immunofluorescence confirmed that about 77% of these nestin-immunoreactive cells exhibited GFAP-immunoreactivity, indicating that a large percentage of nestin-expressing cells may have committed to astroglial cells. In developing mice, down-regulation of nestin expression was observed between P7 and P14. Although co-expression of nestin and NeuN occurred in cortical neurons of P2-7 mice, nestin-containing cells showing NeuN-immunoreactivity disappeared in CNS in older animals. Our results reveal the distribution pattern of nestin-containing neural precursors in the postnatal CNS and provide evidence on their differentiation fate to neurons and astrocytes, suggesting that nestin-containing glial cells may play an important role in remodeling and repairing in the postnatal and adult central nervous system.

Effect of hyperthermia on the transport of mRNA encoding the extracellular matrix glycoprotein SC1 into Bergmann glial cell processes

SC1 is an extracellular matrix glycoprotein that is related to the multifunctional protein SPARC. These matricellular members play regulatory roles in modulating cellular interactions. SC1 expression is enriched in the central nervous system during embryonic and postnatal development as well as in the adult brain. In the rat cerebellum, SC1 is expressed at high levels in Bergmann glial cells and their radial fibers which project into the synaptic-rich molecular layer. At specific stages of development and in the adult, SC1 mRNA is selectively transported into cellular processes of these cells. In the present study, we have examined the effect of whole-body hyperthermia on the transport of SC1 mRNA in Bergmann glial cells of the rat cerebellum. Our results show that SC1 mRNA transport is diminished at 10 and 15 h post-hyperthermia, but returns to control levels by 24 h after heat shock. One of the characteristics of a heat shock on cells grown in tissue culture is a collapse of the cytoskeletal network. Intact components of the cytoskeleton are necessary for the transport of mRNA into peripheral processes of cells. However, in vivo hyperthermia does not appear to affect the morphology of the intermediate filament proteins GFAP, vimentin, or the beta-tubulin component of microtubules in Bergmann glial cell processes. During the hyperthermic time course, levels of vimentin protein increase, which is reflected by immunoreactivity of activated astrocytes and microvasculature in cerebellar white matter.

Significant up-regulation of nestin protein in the neostriatum of MPTP-treated mice. Are the striatal astrocytes regionally activated after systemic MPTP administration?

We are interested in the possible role of central glial cells in pathogenesis of Parkinson's disease of mammals. Parkinsonism model was induced by systemic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration, and the reactive glial cells were examined by immunocytochemical visualization of nestin protein in the brains and spinal cords of C57 mice. Abundant nestin-like immunoreactivity was predominately found in the caudate putamen of MPTP-treated mice and about 481-fold of nestin-like immunoreactive cells increased compared with that of control animals, indicating that significant up-regulation of nestin protein occurred in these regions. Majority of nestin-like immunoreactive cells characterized with astrocytic profiles of multiple, radical and hypotrophic processes, and showed a distribution and dynamic patterns similar to that of glial fibrillary acid protein (GFAP)-immunoreactive cells in the caudate putamen. Double immunofluorescence confirmed that 100% of nestin-like immunoreactive cells exhibited GFAP-immunoreactivity while nestin/GFAP double-labeled cells constituted about 84% of total GFAP-immunoreactive cells in the caudate putamen, indicating these nestin-like immunoreactive cells belong to a reactive population of the astrocytes. On the other hand, no obvious changes of nestin- or GFAP-like immunoreactivities were detected in the globus pallidus, the substantia nigra and the ventral tegmental area after MPTP-treatment. The results have provided morphological evidence for the regional activation of astrocytic glial cells following systemic MPTP administration, suggesting that a large population of reactive striatal astrocytes might play an important role in initial pathogenesis or acute stage of Parkinson's disease in mammals.