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Dive into the research topics where Alexander von Holst is active.

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Featured researches published by Alexander von Holst.


Development | 2007

Chondroitin sulfate glycosaminoglycans control proliferation, radial glia cell differentiation and neurogenesis in neural stem/progenitor cells

Swetlana Sirko; Alexander von Holst; Andrea Wizenmann; Magdalena Götz; Andreas Faissner

Although the local environment is known to regulate neural stem cell (NSC) maintenance in the central nervous system, little is known about the molecular identity of the signals involved. Chondroitin sulfate proteoglycans (CSPGs) are enriched in the growth environment of NSCs both during development and in the adult NSC niche. In order to gather insight into potential biological roles of CSPGs for NSCs, the enzyme chondroitinase ABC (ChABC) was used to selectively degrade the CSPG glycosaminoglycans. When NSCs from mouse E13 telencephalon were cultivated as neurospheres, treatment with ChABC resulted in diminished cell proliferation and impaired neuronal differentiation, with a converse increase in astrocytes. The intrauterine injection of ChABC into the telencephalic ventricle at midneurogenesis caused a reduction in cell proliferation in the ventricular zone and a diminution of self-renewing radial glia, as revealed by the neurosphere-formation assay, and a reduction in neurogenesis. These observations suggest that CSPGs regulate neural stem/progenitor cell proliferation and intervene in fate decisions between the neuronal and glial lineage.


The Journal of Neuroscience | 2006

The Unique 473HD-Chondroitinsulfate Epitope Is Expressed by Radial Glia and Involved in Neural Precursor Cell Proliferation

Alexander von Holst; Swetlana Sirko; Andreas Faissner

Neural stem cells have been documented in both the developing and the mature adult CNSs of mammals. This cell population holds a considerable promise for therapeutical applications in a wide array of CNS diseases. Therefore, universally applicable strategies for the purification of this population to further its cell biological characterization are sought. Here, we report that the unique chondroitin sulfate epitope recognized by the monoclonal antibody 473HD is surface expressed on actively cycling, multipotent progenitor cells of the developing telencephalon with radial glia-like properties. When used for immunopanning, the antibody enriched at least threefold for neural stem/progenitor cells characterized by the ability to self-renew as neurospheres that generated all major neural lineages in differentiation assays. In contrast, the 473HD-depleted cell fraction was mostly devoid of neurosphere-forming cells. The isolation of 473HD-positive adult multipotent progenitors from the subependymal zone of the lateral ventricle wall revealed a substantial overlap with the known adult neural stem cell marker LewisX. When the chondroitin sulfates were removed from immunoselected 473HD-positive neural stem/progenitor cell surfaces by chondroitinase ABC treatment or perturbed by the monoclonal antibody 473HD that recognizes the unique DSD-1 chondroitin sulfate epitope, the generation of neurospheres was significantly reduced. Thus, the 473HD epitope could not only be used for the isolation of multipotent neural progenitors during forebrain development as well as from the adult neurogenic niche but may also constitute a functionally important entity of the neural stem cell niche.


Stem Cells | 2008

Expression of multiple chondroitin/dermatan sulfotransferases in the neurogenic regions of the embryonic and adult central nervous system implies that complex chondroitin sulfates have a role in neural stem cell maintenance.

Kaoru Akita; Alexander von Holst; Yoko Furukawa; Tadahisa Mikami; Kazuyuki Sugahara; Andreas Faissner

Chondroitin/dermatan sulfotransferases (C/D‐STs) underlie the synthesis of diverse sulfated structures in chondroitin/dermatan sulfate (CS/DS) chains. Recent reports have suggested that particular sulfated structures on CS/DS polymers are involved in the regulation of neural stem cell proliferation. Here, we examined the gene expression profile of C/D‐STs in the neurogenic regions of embryonic and adult mouse central nervous system. Using reverse transcription‐polymerase chain reaction analysis, all presently known C/D‐STs were detected in the dorsal and ventral telencephalon of the embryonic day 13 (E13) mouse embryo, with the exception of chondroitin 4‐O‐sulfotransferase (C4ST)‐3. In situ hybridization for C4ST‐1, dermatan 4‐O‐sulfotransferase‐1, chondroitin 6‐O‐sulfotransferase (C6ST)‐1 and ‐2, and uronosyl 2‐O‐sulfotransferase revealed a cellular expression of these sulfotransferase genes in the embryonic germinal zones of the forebrain. The expression of multiple C/D‐STs is maintained on cells residing in the adult neural stem cell niche. Neural stem cells cultured as neurospheres maintained the expression of these enzymes. Consistent with the gene expression pattern of C/D‐STs, disaccharide analysis revealed that neurospheres and E13 mouse brain cells synthesized CS/DS chains containing monosulfated, but also significant amounts of disulfated, disaccharide units. Functionally, the inhibition of sulfation with sodium chlorate resulted in a significant, dose‐dependent decrease in neurosphere number that could not be rescued by the addition of individual purified glycosaminoglycan (GAG) chains, including heparin. These findings argue against a simple charge‐based mechanism of GAG chains in neural stem cell maintenance. The synergistic activities of C/D‐STs might allow for the adaptive modification of CS/DS proteoglycans with diversely sulfated CS/DS chains in the extracellular microenvironment that surrounds neural stem cells.


Journal of Biological Chemistry | 2007

Neural stem/progenitor cells express 20 tenascin C isoforms that are differentially regulated by Pax6.

Alexander von Holst; Ursula Egbers; Alain Prochiantz; Andreas Faissner

Tenascin C (Tnc) is an alternatively spliced, multimodular extracellular matrix glycoprotein present in the ventricular zone of the developing brain. Pax6-deficient small eye (sey) mouse mutants show an altered Tnc expression pattern. Here, we investigated the expression of Tnc isoforms in neural stem/progenitor cells and their regulation by the paired-box transcription factor Pax6. Neural stem/progenitor cells cultured as neurospheres strongly expressed Tnc on the protein level. The Tnc isoform expression in neural stem/progenitor cells was analyzed by reverse transcriptase-PCR and dot blot Southern hybridization. In total, 20 different Tnc isoforms were detected in neurospheres derived from embryonic fore-brain cell suspensions. The Tnc isoform containing the fibronectin type III domains A1A4BD is novel and might be neural stem/progenitor cell-specific. Transient overexpression of Pax6 in neurospheres of the medial ganglionic eminence did not alter the total Tnc mRNA expression level but showed a pronounced regulative effect on different Tnc isoforms. The larger Tnc isoforms containing four, five, and six additional alternatively spliced fibronectin type III domains were up-regulated, whereas the small Tnc isoforms without any or with one additional domain were down-regulated. Thus, Pax6 is a homeodomain protein that also modulates the splicing machinery. We conclude that the combinatorial code of Tnc isoform expression in the neural stem/progenitor cell is complex and regulated by Pax6. These findings suggest a functional significance for individual Tnc isoforms in neural stem/progenitor cells.


Stem Cells | 2010

Chondroitin Sulfates Are Required for Fibroblast Growth Factor‐2‐Dependent Proliferation and Maintenance in Neural Stem Cells and for Epidermal Growth Factor‐Dependent Migration of Their Progeny

Swetlana Sirko; Alexander von Holst; Anika Weber; Andrea Wizenmann; Ursula Theocharidis; Magdalena Götz; Andreas Faissner

The neural stem cell niche of the embryonic and adult forebrain is rich in chondroitin sulfate glycosaminoglycans (CS‐GAGs) that represent complex linear carbohydrate structures on the cell surface of neural stem/progenitor cells or in their intimate environment. We reported earlier that the removal of CS‐GAGs with the bacterial enzyme chondroitinase ABC (ChABC) reduced neural stem/progenitor cell proliferation and self‐renewal, whereas this treatment favored astroglia formation at the expense of neurogenesis. Here, we studied the consequences of CS‐deglycanation further and revealed that CS‐GAGs are selectively required for neurosphere formation, proliferation, and self‐renewal of embryonic cortical neural stem/progenitor cells in response to fibroblast growth factor (FGF)‐2. Consistently, the FGF‐2‐dependent activation of the MAPKinase in neural stem/progenitor cells was diminished after ChABC treatment, but unaltered after epidermal growth factor (EGF) stimulation. Upon EGF treatment, fewer radial glia were brain lipid‐binding protein (BLBP)‐positive, whereas more were glutamate aspartate transporter (GLAST)‐positive after CS‐GAG removal. Only in this latter situation, GLAST‐positive radial glia cells extended processes that supported neuronal migration from differentiating neurospheres. CS‐deglycanation also selectively increased astrocyte numbers and their migration in response to EGF. Thus, our approach revealed that CS‐GAGs are essential for FGF‐2‐mediated proliferation and maintenance of neuron‐generating neural stem/progenitor cells. Simultaneously, CS‐GAGs act as a brake on the EGF‐dependent maturation, migration, and gliogenesis of neural stem/progenitor cells. We conclude that neural stem/progenitor cell subpopulations reside in neurospheres that are distinguishable by their responsiveness to FGF‐2 and EGF which is differentially regulated by CS‐carbohydrate structures. STEM CELLS 2010;28:775–787


Glia | 2009

Tenascin C and tenascin R similarly prevent the formation of myelin membranes in a RhoA-dependent manner, but antagonistically regulate the expression of myelin basic protein via a separate pathway

Tim Czopka; Alexander von Holst; Gudula Schmidt; Charles ffrench-Constant; Andreas Faissner

Membrane formation and the initiation of myelin gene expression are hallmarks of the differentiation of oligodendrocytes from their precursors. Here, we compared the roles of the two related extracellular matrix (ECM) glycoproteins Tenascin C (Tnc) and Tenascin R (Tnr) in oligodendrocyte differentiation. Oligodendrocyte precursors from Tnr‐deficient mice exhibited reduced differentiation, as revealed by retarded expression of myelin basic protein (MBP) in culture. This could be rescued with purified Tnr. In contrast, when we cultured oligodendrocytes on a Tnc‐containing, astrocyte‐derived ECM, they barely expressed MBP. This inhibition could be overcome when we used ECM from astrocytes deficient for Tnc, suggesting that Tnc inhibits differentiation. In contrast to their antagonistic effect on differentiation, both Tnc and Tnr similarly inhibited morphologic maturation. When oligodendrocytes were cultured on the purified glycoproteins, process elaboration and membrane expansion were reduced. Both Tnc and Tnr interfered with the activation of the small GTPase RhoA. Conversely, RhoA and Rac1 activation induced by cytotoxic necrotizing factor 1 (CNF1) increased the formation of myelin membranes, whereas Y27632‐mediated inhibition of the Rho‐cascade prevented it without, however, affecting the fraction of MBP‐expressing cells. Because Tnc and Tnr play antagonistic roles for differentiation and comparably inhibit morphologic maturation, we conclude that independent molecular pathways regulate these processes.


Brain | 2009

Focal laser-lesions activate an endogenous population of neural stem/progenitor cells in the adult visual cortex

Swetlana Sirko; Angela Neitz; Thomas Mittmann; Andrea Horvat-Bröcker; Alexander von Holst; Ulf T. Eysel; Andreas Faissner

CNS lesions stimulate adult neurogenic niches. Endogenous neural stem/progenitor cells represent a potential resource for CNS regeneration. Here, we investigate the response to unilateral focal laser-lesions applied to the visual cortex of juvenile rats. Within 3 days post-lesion, an ipsilateral increase of actively cycling cells was observed in cortical layer one and in the callosal white matter within the lesion penumbra. The cells expressed the neural stem/progenitor cell marker Nestin and the 473HD-epitope. Tissue prepared from the lesion area by micro-dissection generated self-renewing, multipotent neurospheres, while cells from the contralateral visual cortex did not. The newly formed neural stem/progenitor cells in the lesion zone might support neurogenesis, as suggested by the expression of Pax6 and Doublecortin, a marker of newborn neurons. We propose that focal laser-lesions may induce the emergence of stem/progenitor cells with neurogenic potential. This could underlie the beneficial effects of laser application in neurosurgery.


Molecular and Cellular Neuroscience | 1995

Retinoic Acid-Mediated Increase in TrkA Expression Is Sufficient to Elicit NGF-Dependent Survival of Sympathetic Neurons

Alexander von Holst; Alfredo Rodríguez-Tébar; Jean-Jacques Michaille; Danielle Dhouailly; Anders Bäckström; Ted Ebendal; Hermann Rohrer

Sympathetic neurons depend on the classical neurotrophin NGF for survival by the time they innervate their targets, but the mechanisms controlling the onset of NGF responsiveness in developing neuroblasts have not been defined. Immature chick sympathetic neurons are unresponsive to NGF, but express low mRNA levels of the high-affinity NGF receptor trkA. Treatment with retinoic acid (RA) leads to increased levels of both trkA mRNA and protein, a response mediated through retinoic acid receptor alpha (RAR alpha). Ectopic expression of trkA in these cells results in the ability to survive with NGF, suggesting that RA-induced trkA expression is sufficient to elicit NGF-dependent survival. Our data establish a mechanism controlling NGF responsiveness and implicate a function for RA at defined late stages of neuron development.


The Journal of Neuroscience | 2010

Regulatory Mechanisms that Mediate Tenascin C-Dependent Inhibition of Oligodendrocyte Precursor Differentiation

Tim Czopka; Alexander von Holst; Charles ffrench-Constant; Andreas Faissner

Here, we present mechanisms for the inhibition of oligodendendrocyte precursor cell (OPC) differentiation, a biological function of neural extracellular matrix (ECM). The differentiation of oligodendrocytes is orchestrated by a complex set of stimuli. In the present study, we investigated the signaling pathway elicited by the ECM glycoprotein tenascin C (Tnc). Tnc substrates inhibit myelin basic protein (MBP) expression of cultured rat oligodendrocytes, and, conversely, we found that the emergence of MBP expression is accelerated in forebrains of Tnc-deficient mice. Mechanistically, Tnc interfered with phosphorylation of Akt, which in turn reduced MBP expression. At the cell surface, Tnc associates with lipid rafts in oligodendrocyte membranes, together with the cell adhesion molecule contactin (Cntn1) and the Src family kinase (SFK) Fyn. Depletion of Cntn1 in OPCs by small interfering RNAs (siRNAs) abolished the Tnc-dependent inhibition of oligodendrocyte differentiation, while Tnc exposure impeded the activation of the tyrosine kinase Fyn by Cntn1. Concomitant with oligodendrocyte differentiation, Tnc antagonized the expression of the signaling adaptor and RNA-binding molecule Sam68. siRNA-mediated knockdown or overexpression of Sam68 delayed or accelerated oligodendrocyte differentiation, respectively. Inhibition of oligodendrocyte differentiation with the SFK inhibitor PP2 could be rescued by Sam68 overexpression, which may indicate a regulatory role for Sam68 downstream of Fyn. Our study therefore uncovers the first signaling pathways that underlie Tnc-induced, ECM-dependent maintenance of the immature state of OPCs.


Cells Tissues Organs | 2008

Tenascin C in stem cell niches: redundant, permissive or instructive?

Alexander von Holst

The stem cell niche provides the specialized environment that is able to sustain the lifelong maintenance of stem cells in their discrete locations within organs. The niche is usually composed of seveThe stem cell niche provides the specialized environment that is able to sustain the lifelong maintenance of stem cells in their discrete locations within organs. The niche is usually composed of several different cell types and a specialized extracellular matrix consisting of many different constituents. Additionally, a variety of growth factors are secreted into the extracellular space and contribute to the functional organization of the niche. Here, I will concentrate on the multimodular extracellular matrix glycoprotein tenascin C (Tnc) and discuss it as an exemplary molecule that is present in several stem cell niches. In spite of its intuitively suggestive presence, it has been difficult to provide functional evidence for the importance of Tnc in the context of stem cells. In the nervous system, the careful analysis of Tnc-deficient mice has revealed that the developmental program neural stem cell pass-through is delayed due to changes in growth factor responsiveness. To gain further insight, we have employed the gene trap technology in neural stem cells to identify potential Tnc target genes. This approach has surfaced 2 interesting candidates that may contribute to a better understanding of the signal(s) elicited by Tnc in neural stem/progenitor cells in the niche.

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Tim Czopka

Ruhr University Bochum

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Jeroen Demmers

Erasmus University Rotterdam

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Raymond A. Poot

Erasmus University Rotterdam

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Umut Akinci

Erasmus University Rotterdam

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