A rod end deletion in the intermediate filament protein nestin alters its subcellular localization in neuroepithelial cells of transgenic mice

Nestin promotes the phosphorylation-dependent disassembly of vimentin intermediate filaments during mitosis

The expression of the intermediate filament (IF) protein nestin is closely associated with rapidly proliferating progenitor cells during neurogenesis and myogenesis, but little is known about its function. In this study, we examine the effects of nestin expression on the assembly state of vimentin IFs in nestin-free cells. Nestin is introduced by transient transfection and is positively correlated with the disassembly of vimentin IFs into nonfilamentous aggregates or particles in mitotic but not interphase cells. This nestin-mediated disassembly of IFs is dependent on the phosphorylation of vimentin by the maturation/M-phase-promoting factor at ser-55 in the amino-terminal head domain. In addition, the disassembly of vimentin IFs during mitosis appears to be a unique feature of nestin-expressing cell types. Furthermore, when the expression of nestin is downregulated by the nestin-specific small interfering RNA in nestin-expressing cells, vimentin IFs remain assembled throughout all stages of mitosis. Previous studies suggest that nonfilamentous vimentin particles are IF precursors and can be transported rapidly between different cytoplasmic compartments along microtubule tracks. On the basis of these observations, we speculate that nestin may play a role in the trafficking and distribution of IF proteins and potentially other cellular factors to daughter cells during progenitor cell division.

Repetitive spreading depression induces nestin protein expression in the cortex of rats and mice. Is this upregulation initiated by N-methyl-D-aspartate receptors?

In the November issue (2001) of Neuroscience Letters, Holmin et al. (Neurosci. Lett. 314 (2001) 151) reported that the synthesis of the intermediate filament protein nestin was upregulated by potassium-induced depolarization in the rat cortex. In this letter, we provide supplementary evidence that repeated cortical spreading depression elicited by potassium induces a delayed upregulation of nestin. However, we argue against the authors' conclusion, "Nestin expression was N-methyl-D-aspartate (NMDA)-receptor dependent since dizocilpine (MK-801) treatment abolished the response" because spreading depression itself is very sensitive to NMDA-receptor block, and the drug treatment was initiated prior to potassium application to the cortex in Holmin et al.'s study.

Immunohistochemical detection of nestin in pediatric brain tumors

Nestin is an intermediate filament protein (IFP) expressed in undifferentiated cells during CNS development and in CNS tumors. Previous studies have arrived at different conclusions in terms of which types of CNS tumors express nestin. In this report we establish an immunohistochemical protocol using antigen retrieval, which significantly enhances staining with two polyclonal anti-nestin antisera, #130 and #4350. The staining pattern was identical for the two nestin antisera and very similar to that of vimentin, while glial fibrillary acidic protein (GFAP), immunoreactivity was absent from 9.5-week-old forebrain. The current study of 20 primary CNS tumors from pediatric patients included seven ependymomas, seven primitive neuroectodermal tumors (PNETs), five pilocytic astrocytomas, and one glioblastoma multiforme (GBM). All these tumors expressed nestin to various extents, in contrast to five brain metastases tested. Strong nestin immunoreactivity was found in malignant primary CNS tumors, whereas benign pilocytic astrocytomas showed low but consistent nestin expression. In all tumors nestin immunoreactivity was confined to the cytoplasm of tumor cells and was co-expressed with astrocyte markers vimentin, GFAP, and S-100. Vascular endothelial cells of all neoplasms also showed marked immunoreactivity for nestin and vimentin, whereas they were negative for GFAP and S-100. In conclusion, antiserum #4350 detected nestin in formalin-fixed, paraffin-embedded tissue sections by heat-induced antigen retrieval immunohistochemistry. Nestin was expressed in both highly malignant and low malignant gliomas, indicating the potential use of nestin as a diagnostic tumor marker in surgical pathology.

Expression of the intermediate filament protein nestin by sustentacular cells in mature olfactory neuroepithelium

The intermediate filament protein nestin has been widely used as a marker for proliferating neural progenitor cells in the nervous system. The mammalian olfactory neuroepithelium is a region of the nervous system that robustly supports ongoing neurogenesis, yet where nestin has not been reported to mark proliferating progenitors. Using immunohistochemistry, we examined nestin expression in the mature olfactory neuroepithelium and found it to be tightly restricted to the basal compartment where the olfactory neuronal progenitor cell population resides. The pattern of nestin immunoreactivity was consistent with expression by the endfeet and inferior processes of sustentacular cells rather than basal cells. Using a bank of defined antibody markers, we confirmed nestin's pattern of distribution to be different from that of cytokeratin, vimentin, GBC-1, GAP43, and carnosine. It was highly similar to the pattern of SUS-4 immunoreactivity in the basal region of the neuroepithelium. Following surgical bulbectomy, nestin expression was up-regulated and became evident in the cell bodies of sustentacular cells situated more apically in the neuroepithelium. We have shown nestin to be present in the basal region of the adult olfactory neuroepithelium in the zone that supports ongoing neurogenesis in the adult, but its expression is restricted to the inferior parts of sustentacular cells rather than the neuronal progenitor cells. Nestin may play a potential role in the migration of recently proliferated olfactory neurons on the scaffolding of sustentacular cells in a manner analogous to its proposed role in radial glia during embryonic development of the central nervous system.

Platelet-derived growth factor receptor-alpha in ventricular zone cells and in developing neurons

Cells in the early neuroepithelium differentiate and give rise to all cells in the central nervous system (CNS). The ways from a multipotent CNS stem cell to specialized neurons and glia are not fully understood. Using immunohistochemistry we found that neuroepithelial cells express the platelet-derived growth factor receptor-alpha (PDGFR-alpha) in the neural plate at embryonic day 8.5 and onwards in the neural tube. The protein was polarized to ventricular endfeet. Furthermore, PDGFR-alpha expression was localized to cells undergoing early neuronal development. We also found PDGFR-alpha expression in developing granule cells in the postnatal cerebellum, in Purkinje cells in the adult cerebellum and on processes of developing dorsal root ganglion cells. Previous reports mainly describe PDGFR-alpha expression in oligodendrocyte precursors and glial cells. We believe, in line with a few previous reports, that the PDGFR-alpha in addition marks a pool of undifferentiated cells, which are able to differentiate into neurons.

Paranemin and the organization of desmin filament networks

De novo expression of vimentin, GFAP or peripherin leads to the assembly of an extended intermediate filament network in intermediate filament-free SW13/cl.2 cells. Desmin, in contrast, does not form extended filament networks in either SW13/cl.2 or intermediate filament-free mouse fibroblasts. Rather, desmin formed short thickened filamentous structures and prominent spot-like cytoplasmic aggregates that were composed of densely packed 9–11 nm diameter filaments. Analysis of stably transfected cell lines indicates that the inability of desmin to form extended networks is not due to a difference in the level of transgene expression. Nestin, paranemin and synemin are large intermediate filament proteins that coassemble with desmin in muscle cells. Although each of these large intermediate filament proteins colocalized with desmin when coexpressed in SW-13 cells, expression of paranemin, but not synemin or nestin, led to the formation of an extended desmin network. A similar rescue of desmin network organization was observed when desmin was coexpressed with vimentin, which coassembles with desmin, or with keratins, which formed a distinct filament network. These studies demonstrate that desmin filaments differ in their organizational properties from the other vimentin-like intermediate filament proteins and appear to depend upon coassembly with paranemin, at least when they are expressed in non-muscle cells, in order to form an extended filament network.

Nestin expression in embryonic and adult human teeth under normal and pathological conditions

Nestin is an intermediate filament most related to neurofilaments and expressed predominantly in the developing nervous system and muscles. In the present study we examined the in vivo distribution of nestin in human teeth during embryonic development and in permanent teeth under normal and pathological conditions. The results show that nestin is first expressed at the bell stage and that its distribution is restricted in pulpal cells located at the cusp area of the fetal teeth. In young permanent teeth, nestin is found only in functional odontoblasts, which produce the hard tissue matrix of dentin. Expression is progressively down-regulated and nestin is absent from older permanent teeth. In carious and injured teeth, nestin expression is up-regulated in a selective manner in odontoblasts surrounding the injury site, showing a link between tissue repair competence and nestin up-regulation under pathological conditions. In an in vitro assay system of human dental pulp explants, nestin is up-regulated after local application of bone morphogenic protein-4. A similar effect is seen in cultures of primary pulp cells during their differentiation into odontoblasts. Taken together, these results suggest that nestin plays a potential role in odontoblast differentiation during normal and pathological conditions and that bone morphogenic protein-4 is involved in nestin up-regulation.

Molecular characteristics and interactions of the intermediate filament protein synemin. Interactions with alpha-actinin may anchor synemin-containing heterofilaments

Synemin is a cytoskeletal protein originally identified as an intermediate filament (IF)-associated protein because of its colocalization and copurification with the IF proteins desmin and vimentin in muscle cells. Our sequencing studies have shown that synemin is an unusually large member (1,604 residues, 182,187 Da) of the IF protein superfamily, with the majority of the molecule consisting of a long C-terminal tail domain. Molecular interaction studies demonstrate that purified synemin interacts with desmin, the major IF protein in mature muscle cells, and with alpha-actinin, an integral myofibrillar Z-line protein. Furthermore, expressed synemin rod and tail domains interact, respectively, with desmin and alpha-actinin. Analysis of endogenous protein expression in SW13 clonal lines reveals that synemin is coexpressed and colocalized with vimentin IFs in SW13.C1 vim+ cells but is absent in SW13.C2 vim- cells. Transfection studies indicate that synemin requires the presence of another IF protein, such as vimentin, in order to assemble into IFs. Taken in toto, our results suggest synemin functions as a component of heteropolymeric IFs and plays an important cytoskeletal cross-linking role by linking these IFs to other components of the cytoskeleton. Synemin in striated muscle cells may enable these heterofilaments to help link Z-lines of adjacent myofibrils and, thereby, play an important role in cytoskeletal integrity.

Intermediate filament protein partnership in astrocytes

Intermediate filaments are general constituents of the cytoskeleton. The function of these structures and the requirement for different types of intermediate filament proteins by individual cells are only partly understood. Here we have addressed the role of specific intermediate filament protein partnerships in the formation of intermediate filaments in astrocytes. Astrocytes may express three types of intermediate filament proteins: glial fibrillary acidic protein (GFAP), vimentin, and nestin. We used mice with targeted mutations in the GFAP or vimentin genes, or both, to study the impact of loss of either or both of these proteins on intermediate filament formation in cultured astrocytes and in normal or reactive astrocytes in vivo. We report that nestin cannot form intermediate filaments on its own, that vimentin may form intermediate filaments with either nestin or GFAP as obligatory partners, and that GFAP is the only intermediate filament protein of the three that may form filaments on its own. However, such filaments show abnormal organization. Aberrant intermediate filament formation is linked to diseases affecting epithelial, neuronal, and muscle cells. Here we present models by which the normal and pathogenic functions of intermediate filaments may be elucidated in astrocytes.

Co-expression of nestin and vimentin intermediate filaments in invasive human astrocytoma cells

Intermediate filaments (IFs) are highly diverse intracytoplasmic proteins within the cytoskeleton which exhibit cell type specificity of expression. A growing body of evidence suggests that IFs may be involved as collaborators in complex cellular processes controlling astrocytoma cell morphology, adhesion and proliferation. As the co-expression of different IF subtypes has been linked to enhanced motility and invasion in a number of different cancer subtypes, we undertook the present study to examine the expression of vimentin and nestin in a panel of human astrocytoma cell lines whose tumorigenicity, invasiveness and cytoskeletal protein profiles are well known. Astrocytoma cells were examined for IF protein expression by immunofluorescence confocal and immunoelectron microscopy. The motility of all cell lines was determined by computerized time-lapse videomicroscopy. Invasive potential of astrocytoma cells was determined using Matrigel as a barrier to astrocytoma cell invasion in vitro. Vimentin was expressed by all astrocytoma cell lines. On the other hand, nestin was variably expressed among the different cell lines. The most motile and invasive astrocytoma cell line in our study was antisense GFAP-transfected U251 (asU251) astrocytoma cells which showed marked up-regulation of nestin expression compared to the U251 parental cell line and controls. The U87 astrocytoma cell line also demonstrated high nestin expression levels and was associated with an increased basal motility rate and a high degree of invasiveness through Matrigel. U343 astrocytoma cells did not express nestin, but had high levels of GFAP. It had the lowest motility rate and invasiveness of all the astrocytoma cell lines examined. Taken together, these data suggest that for the astrocytoma cell lines examined in this study, nestin and vimentin co-expression may serve as a marker for an astrocytoma cell type with enhanced motility and invasive potential. Further studies are required to determine the mechanism by which dual-IF protein expression alters other cytoskeletal or cell surface receptor protein components important in the process of astrocytoma invasion.

Abnormal reaction to central nervous system injury in mice lacking glial fibrillary acidic protein and vimentin

In response to injury of the central nervous system, astrocytes become reactive and express high levels of the intermediate filament (IF) proteins glial fibrillary acidic protein (GFAP), vimentin, and nestin. We have shown that astrocytes in mice deficient for both GFAP and vimentin (GFAP-/-vim-/-) cannot form IFs even when nestin is expressed and are thus devoid of IFs in their reactive state. Here, we have studied the reaction to injury in the central nervous system in GFAP-/-, vimentin-/-, or GFAP-/-vim-/- mice. Glial scar formation appeared normal after spinal cord or brain lesions in GFAP-/- or vimentin-/- mice, but was impaired in GFAP-/-vim-/- mice that developed less dense scars frequently accompanied by bleeding. These results show that GFAP and vimentin are required for proper glial scar formation in the injured central nervous system and that some degree of functional overlap exists between these IF proteins.

Identification of both general and region-specific embryonic CNS enhancer elements in the nestin promoter

In this report, we investigate how nestin expression is controlled in neural progenitor cells of the embryonic CNS. A 374-bp region in the second intron of the human nestin gene is sufficient, and a 120-bp sequence in this region is required, to express the lacZ reporter gene throughout the developing CNS of E9.5-10.5 transgenic mouse embryos. The 120-bp element region contains putative binding sites for nuclear hormone receptors and we show that TRs, RXR, RAR, and COUP-TF bind to these motifs. A separate enhancer, located most probably 5' to the 120-bp sequence in the second intron, controls midbrain expression at E10.5. In conclusion, our data show that the nestin enhancer in the second intron contains elements both for general and for region-specific CNS progenitor cell expression and suggest that nuclear hormone receptors play a role in the regulation of nestin expression in the early CNS.