Biomedical subjects

J Frisén

Publications and source records attributed to J Frisén.

At least 37 records · Page 2Linked to original sources

PubMed1998

Retinoid-X receptor signalling in the developing spinal cord.

Retinoids regulate gene expression through the action of retinoic acid receptors (RARs) and retinoid-X receptors (RXRs), which both belong to the family of nuclear hormone receptors. Retinoids are of fundamental importance during development, but it has been difficult to assess the distribution of ligand-activated receptors in vivo. This is particularly the case for RXR, which is a critical unliganded auxiliary protein for several nuclear receptors, including RAR, but its ligand-activated role in vivo remains uncertain. Here we describe an assay in transgenic mice, based on the expression of an effector fusion protein linking the ligand-binding domain of either RXR or RAR to the yeast Gal4 DNA-binding domain, and the in situ detection of ligand-activated effector proteins by using an inducible transgenic lacZ reporter gene. We detect receptor activation in the spinal cord in a pattern that indicates that the receptor functions in the maturation of limb-innervating motor neurons. Our results reveal a specific activation pattern of Gal4-RXR which indicates that RXR is a critical bona fide receptor in the developing spinal cord.

Animals↗

PubMed1998

Nerve growth factor induces process formation in meningeal cells: implications for scar formation in the injured CNS.

Nerve growth factor (NGF) induces the differentiation and supports the survival of subpopulations of neurons in the PNS and CNS. Here we report that meningeal cells in the pia mater express immunoreactivity and mRNA for both known NGF receptors, the low-affinity receptor p75 and the tyrosine kinase receptor trkA. NGF induces rapid tyrosine phosphorylation of trkA in meningeal cells in vitro. NGF does not stimulate proliferation of primary meningeal cells but induces process outgrowth. p75- and trkA-immunoreactive meningeal cells with long processes, resembling NGF-treated cells in vitro, are abundant in the scar tissue that forms at spinal cord lesions in rat and cat. These data suggest that NGF, which is expressed at increased levels in the brain and spinal cord after lesions, may be involved in scar formation in the injured CNS.

Animals↗

PubMed1998

Central nervous system stem cells in the embryo and adult.

The central nervous system is generated from neural stem cells during embryonic development. These cells are multipotent and generate neurons, astrocytes and oligodendrocytes. The last few years it has been found that there are populations of stem cells also in the adult mammalian brain and spinal cord. In this paper, we review the recent development in the field of embryonic and adult neural stem cells.

Adult↗

PubMed1998

Ephrin-A5 (AL-1/RAGS) is essential for proper retinal axon guidance and topographic mapping in the mammalian visual system.

Ephrin-A5 (AL-1/RAGS), a ligand for Eph receptor tyrosine kinases, repels retinal axons in vitro and has a graded expression in the superior colliculus (SC), the major midbrain target of retinal ganglion cells. These properties implicate ephrin-A5 in the formation of topographic maps, a fundamental organizational feature of the nervous system. To test this hypothesis, we generated mice lacking ephrin-A5. The majority of ephrin-A5-/- mice develop to adulthood, are morphologically intact, and have normal anterior-posterior patterning of the midbrain. However, within the SC, retinal axons establish and maintain dense arborizations at topographically incorrect sites that correlate with locations of low expression of the related ligand ephrin-A2. In addition, retinal axons transiently overshoot the SC and extend aberrantly into the inferior colliculus (IC). This defect is consistent with the high level of ephrin-A5 expression in the IC and the finding that retinal axon growth on membranes from wild-type IC is inhibited relative to that on membranes from ephrin-A5-/- IC. These findings show that ephrin-A5 is required for the proper guidance and mapping of retinal axons in the mammalian midbrain.

Animals↗

PubMed1998

Topographic guidance labels in a sensory projection to the forebrain.

Visual connections to the mammalian forebrain are known to be patterned by neural activity, but it remains unknown whether the map topography of such higher sensory projections depends on axon guidance labels. Here, we show complementary expression and binding for the receptor EphA5 in mouse retina and its ligands ephrin-A2 and ephrin-A5 in multiple retinal targets, including the major forebrain target, the dorsal lateral geniculate nucleus (dLGN). These ligands can act in vitro as topographically specific repellents for mammalian retinal axons and are necessary for normal dLGN mapping in vivo. The results suggest a general and economic modular mechanism for brain mapping whereby a projecting field is mapped onto multiple targets by repeated use of the same labels. They also indicate the nature of a coordinate system for the mapping of sensory connections to the forebrain.

Aging↗

PubMed1997

Aberrant axonal projections in mice lacking EphA8 (Eek) tyrosine protein kinase receptors.

We have generated mice homozygous for a mutation that disrupts the gene encoding EphA8, a member of the Eph family of tyrosine protein kinase receptors, previously known as Eek. These mice develop to term, are fertile and do not display obvious anatomical or physiological defects. The mouse ephA8/eek gene is expressed primarily in a rostral to caudal gradient in the developing tectum. Axonal tracing experiments have revealed that in these mutant mice, axons from a subpopulation of tectal neurons located in the superficial layers of the superior colliculus do not reach targets located in the contralateral inferior colliculus. Moreover, ephA8/eek null animals display an aberrant ipsilateral axonal tract that projects to the ventral region of the cervical spinal cord. Retrograde labeling revealed that these abnormal projections originate from a small subpopulation of superior colliculus neurons that normally express the ephA8/eek gene. These results suggest that EphA8/Eek receptors play a role in axonal pathfinding during development of the mammalian nervous system.

Animals↗

PubMed1997

TrkB signaling is required for postnatal survival of CNS neurons and protects hippocampal and motor neurons from axotomy-induced cell death.

Newborn mice carrying targeted mutations in genes encoding neurotrophins or their signaling Trk receptors display severe neuronal deficits in the peripheral nervous system but not in the CNS. In this study, we show that trkB (-/-) mice have a significant increase in apoptotic cell death in different regions of the brain during early postnatal life. The most affected region in the brain is the dentate gyrus of the hippocampus, although elevated levels of pyknotic nuclei were also detected in cortical layers II and III and V and VI, the striatum, and the thalamus. Furthermore, axotomized hippocampal and motor neurons of trkB (-/-) mice have significantly lower survival rates than those of wild-type littermates. These results suggest that neurotrophin signaling through TrkB receptors plays a role in the survival of CNS neurons during postnatal development. Moreover, they indicate that TrkB receptor signaling protects subpopulations of CNS neurons from injury- and axotomy-induced cell death.

Animals↗

PubMed1997

Ablation of the CDK inhibitor p57Kip2 results in increased apoptosis and delayed differentiation during mouse development.

p57(Kip2) is a paternally imprinted gene that encodes a potent inhibitor of several cyclin/Cdk complexes. p57(Kip2) is primarily expressed in terminally differentiated cells, associates with G1 Cdks, and can cause cell cycle arrest in G1 phase. To investigate the role of p57(Kip2) in vivo, we have ablated the p57(Kip2) gene by homologous recombination in ES cells and generated mice devoid of p57(Kip2) expression. Most p57(Kip2) null mice die after birth and display severe developmental defects with varying degrees of penetrance. As expected, heterozygous mice that inherit a maternal, but not a paternal, targeted allele exhibit similar deficiencies and neonatal death. Developmental defects of p57(Kip2) mutant mice include cleft palate and gastrointestinal abnormalities ranging from an inflated GI tract to loss of the jejunum and ileum. These tissues display a significant increase of apoptotic cells in the absence of p57(Kip2). Most p57(Kip2) mutant mice have short limbs, a defect attributable to abnormal endochondral ossification caused by delayed cell cycle exit during chondrocyte differentiation. A similar defect has been observed in mice lacking p107 and p130, thus suggesting that p57(Kip2) might be an upstream regulator of these Rb-related proteins. The p57(Kip2) locus has been implicated in the Beckwith-Wiedemann syndrome and in the development of sporadic Wilms' tumors and lung carcinomas. To date, we have not observed neoplastic development even in those p57(Kip2) mutant mice that have survived for >5 months of age. These findings indicate that p57(Kip2) has an important role during mouse development that cannot be compensated by other Cdk inhibitors.

Abnormalities, Multiple↗

PubMed1997

Apoptotic death of olfactory sensory neurons in the adult rat.

Olfactory sensory neurons only live for about 1 month in most mammals. It is not fully understood whether the short life span of these neurons is due to necrotic death, or if these cells die by apoptosis. One characteristic of cells undergoing apoptotic cell death is internucleosomal DNA-fragmentation. We have used TdT-mediated dUTP-digoxigenin nick end labeling (TUNEL) to detect cells undergoing DNA-fragmentation in situ. In the intact olfactory epithelium of adult rats a subpopulation of basal immature neuronal progenitor cells, as well as mature olfactory sensory neurons, showed DNA-fragmentation. The number of TUNEL-labeled neurons increased dramatically 1.5 days after transection of the fila olfactoria and declined to control levels by Day 4 after the injury. In order to relate DNA-fragmentation to ultrastructural characteristics of apoptosis we modified the TUNEL-labeling protocol to enable studies of TUNEL-labeled cells in the electron microscope. This confirmed that TUNEL-labeled neurons showed morphological characteristics of apoptosis. The data provide evidence for apoptotic death of neurons in the adult mammalian nervous system. The turnover of olfactory sensory neurons is, at least in part, regulated by apoptosis and disruption of the contact with the olfactory bulb results in massive apoptotic death of neurons in the olfactory epithelium.

Animals↗

PubMed1997

Genetic analysis of the role of Eph receptors in the development of the mammalian nervous system.

The Eph family of tyrosine protein kinase receptors and their cognate ligands, a family of membrane-bound molecules known as ephrins, have been implicated in diverse biological processes, such as axon guidance, the formation of topographic neural projections, axon fasciculation, the regionalization of the central nervous system, and cell migration. The recent generation of mutant mice lacking some of these receptors has made possible the dissection of the role that these molecules play in the development of the mammalian nervous system.

Animals↗

PubMed1997

Determinants of axonal regeneration.

Axons often regrow to their targets and lost functions may be restored after an injury in the peripheral nervous system. In contrast, axonal regeneration is generally very limited after injuries in the central nervous system, and functional impairment is usually permanent. The regenerative capacity depends on intrinsic neuronal factors as well as the interaction of neurons with other cells. Glial cells may, in different situations, either support or inhibit axonal growth. This review discusses the molecular mechanisms that are involved in promoting and inhibiting axonal regeneration in the nervous system after injuries.

Animals↗

PubMed1996

Renal agenesis and the absence of enteric neurons in mice lacking GDNF.

Glial-cell-line-derived neurotrophic factor (GDNF) is a potent survival factor for dopaminergic neurons and motor neurons in culture. It also protects these neurons from degeneration in vitro, and improves symptoms like Parkinson's disease induced pharmacologically in rodents and monkeys. Thus GDNF might have beneficial effects in the treatment of Parkinson's disease and amyotrophic lateral sclerosis. To examine the physiological role of GDNF in the development of the mammalian nervous system, we have generated mice defective in GDNF expression by using homologous recombination in embryonic stem cells to delete each of its two coding exons. GDNF-null mice, regardless of their targeted mutation, display complete renal agencies owing to lack of induction of the ureteric bud, an early step in kidney development. These mice also have no enteric neurons, which probably explains the observed pyloric stenosis and dilation of their duodenum. However, ablation of the GDNF gene does not affect the differentiation and survival of dopaminergic neurons, at least during embryonic development.

Animals↗

PubMed1995

Spinal axons in central nervous system scar tissue are closely related to laminin-immunoreactive astrocytes.

Although transected central nervous system axons fail to regrow after injuries in adult mammals, they send sprouts into the scar tissue that forms at the lesion. We have investigated the relation between scar cells, laminin-like immunoreactivity and cut spinal axons in two previously characterized spinal cord lesion types. Labeling with antisera to glial fibrillary acidic protein and laminin demonstrated that the scar tissue formed after lesions in the rat and cat dorsal and ventral funiculi showed prominent gliosis and strong laminin-like immunoreactivity four days to one year postlesion. Axonal sprouts in the scar, visualized with antibodies to neurofilament (RT97) or by tracing using fluorescein-conjugated dextran, were ensheathed by a thin layer of strongly laminin-immunoreactive tissue. Immunoelectron microscopy demonstrated that axons in the scar were ensheathed predominantly by astrocytes, and that the surface of the cells outlining the axons in the scar showed strong laminin-like immunoreactivity. Adhesive and neurite orienting properties in the scar tissue were assessed in an in vitro system where PC12 cells were cultured on spinal cord slices from dorsal funiculus-lesioned rats. Very few cells adhered to the spinal cord section except for the part where the scar tissue had formed, where numerous cells were attached. The PC12 cells that had adhered to the scar tissue were mainly seen in parts of the scar that showed laminin-like immunoreactivity and their neurites predominantly followed tissue showing laminin-like immunoreactivity. The close association between axonal sprouts and laminin-like immunoreactivity indicates a role for laminin in axonal growth and/or guidance in the injured spinal cord.

Animals↗

PubMed1995

Rapid, widespread, and longlasting induction of nestin contributes to the generation of glial scar tissue after CNS injury.

Neuronal regeneration does generally not occur in the central nervous system (CNS) after injury, which has been attributed to the generation of glial scar tissue. In this report we show that the composition of the glial scar after traumatic CNS injury in rat and mouse is more complex than previously assumed: expression of the intermediate filament nestin is induced in reactive astrocytes. Nestin induction occurs within 48 hours in the spinal cord both at the site of lesion and in degenerating tracts and lasts for at least 13 months. Nestin expression is induced with similar kinetics in the crushed optic nerve. In addition to the expression in reactive astrocytes, we also observed nestin induction within 48 hours after injury in cells close to the central canal in the spinal cord, while nestin expressing cells at later timepoints were found progressively further out from the central canal. This dynamic pattern of nestin induction after injury was mimicked by lacZ expressing cells in nestin promoter/lacZ transgenic mice, suggesting that defined nestin regulatory regions mediate the injury response. We discuss the possibility that the spatiotemporal pattern of nestin expression reflects a population of nestin positive cells, which proliferates and migrates from a region close to the central canal to the site of lesion in response to injury.

Animals↗

PubMed1994

Increased trkB mRNA expression by axotomized motoneurones.

It has been previously demonstrated that members of the neurotrophin family may prevent death of motoneurones following axotomy. Here we report that the expression of mRNA for full-length trkB, which is a signal transducing receptor for BDNF and NT-4, increases transiently in spinal motoneurones after axotomy in adult rats. Thus, transection of the sciatic nerve resulted in markedly increased levels of trkB mRNA in axotomized motoneurones three days postinjury, while the levels had returned to normal within three weeks. The data support that neurotrophins may be important for survival and/or regeneration of motoneurones after axon lesion.

Animals↗

PubMed1994

trkC-like immunoreactivity in the primate descending serotoninergic system.

In the search for substances with a potential role in plastic responses of spinal motoneurons we have studied the distribution of trkC-like immunoreactivity in the spinal cord of adult monkeys (Macaca fascicularis). The presence of trkC, which is a signal-transducing receptor for neurotrophin-3, was detected by the use of indirect immunofluorescence with a rabbit polyclonal antibody raised against a synthetic peptide corresponding to the carboxy-terminal domain of the mouse trkC-encoded protein, thus detecting only full-length signal-transducing receptors. trkC-immunoreactive fibres/varicosities could be found at all spinal cord levels and the densest innervation was found in the autonomic intermediolateral and Onuf's nuclei, but somatic motoneuron pools also received a significant contribution of trkC-immunoreactive fibres. Terminals immunoreactive for trkC were also seen in the dorsal horn. Double-labelling experiments revealed a high degree of coexistence between trkC- and 5-hydroxytryptamine (serotonin)-like immunoreactivity in all areas except in the dorsal horn. The results of the present study suggest that neurotrophic signalling with an influence on serotoninergic as well as non-serotoninergic inputs to the adult monkey spinal cord is at hand.

Animals↗

PubMed1994

Substance P-, calcitonin gene-related peptide, growth-associated protein-43, and neurotrophin receptor-like immunoreactivity associated with unmyelinated axons in feline ventral roots and pia mater.

The spinal pia mater receives a rich innervation of small sensory axons via the ventral roots. Other sensory axons enter the ventral roots but end blindly or turn abruptly in hairpin loop-like formations and continue in a distal direction. In the present study, the content of substance P (SP)-, calcitonin gene-related peptide (CGRP)-, growth-associated protein (GAP-43)-, and low-affinity neurotrophin receptor protein (p75NGFr)-like immunoreactivity (-LI) associated with these different types of sensory axons was assessed with light and electron microscopic immunohistochemical techniques. In addition, the binding of antibodies against synthetic peptides representing unique sequences of residues in the products of the trk and trkB protooncogenes was analyzed. These genes encode membrane spanning proteins, which have been shown to constitute specific high affinity binding sites for several members of the nerve growth factor family of neurotrophic factors. The results of the present study imply that the ventral root afferents comprise several different types of sensory axons, which all contain SP-, CGRP-, GAP-43-, and p75NGFr-like immunoreactivities. In addition, at least some of the presumed sensory fiber bundles in ventral roots and the pia mater were immunoreactive for the trkB gene product. Moreover, leptomeningeal cells and nonneuronal cells of the ventral roots were shown to bind antibodies to both the trk and trkB gene products. The ventral root afferents seem to share their immunohistochemical pattern with pain-transducing axons at some other locations, such as the tooth pulp. The contents of SP- and CGRP-LI in sensory axons that reach the central nervous system (CNS) through the ventral root indicate that ventral root afferents may be involved in sensory mechanisms, such as the ventral root pain reaction, as well as in the control of the pial blood vessels. The demonstration of GAP-43 and neurotrophin receptor-immunoreactivities associated with unmyelinated fibers in ventral roots and the pia mater is discussed in relation to previous reports on postnatal plasticity in these axonal populations.

Animals↗

PubMed1994

Adhesive/repulsive properties in the injured spinal cord: relation to myelin phagocytosis by invading macrophages.

The vigorous ingrowth of cut CNS axons into peripheral nerve grafts indicates that the lack of neuronal regeneration within the brain and spinal cord cannot be explained merely by CNS neurons having an inherent weak regenerative capacity. Rather, the brain and spinal cord seem to contain molecules that inhibit axonal growth and, indeed, oligodendrocyte myelin has been demonstrated to effectively block nerve fiber growth. Macrophages can in vitro counteract this growth prohibitory property of the CNS. In this study we have examined the recruitment of macrophages and the removal of myelin in relation to neurite adhesive/repulsive properties in the injured spinal cord of adult rats. Cells immunoreactive for the macrophage-specific antibody ED1 rapidly invaded the lesion area after an incision in the dorsal or ventral funiculus. The number of macrophages remained high for several weeks in the scar tissue formed after both these injuries. This type of scar tissue has previously been reported to permit ingrowth and long-term persistence of axons. In the denervated area rostral to a dorsal funiculus transection, no or few ED1-immunoreactive cells were detected within the first month after the injury. However, at subsequent stages an increasing number of macrophages was found in this region. Myelin was removed much more rapidly at the site of the lesion than rostral to this (in the area undergoing Wallerian degeneration). In order to study adhesive/repulsive properties in the injured spinal cord in relation to local myelin content we employed an in vitro system in which PC12 cells were cultured on spinal cord slices. PC12 cells failed to adhere to sections from the intact spinal cord as well as to sections taken rostral to a dorsal funiculus transection, whereas many cells adhered to the glial scar formed at the lesion. Even at 15 months after the injury, very few PC12 cells attached to sections taken rostral to the transection despite the fact that no myelin could be detected in the denervated area at that time. These data suggest that, in addition to myelin-related growth inhibitory molecules, other factors may be involved in the failure of PC12 cells to adhere to the denervated spinal cord. Such factors could also affect axonal regrowth after spinal cord injury. The adhesion of PC12 cells to the lesion area may be a result of a locally high content of extracellular matrix molecules and/or cell adhesion molecules, factors which are not expressed in the region undergoing Wallerian degeneration.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗