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T J Kilpatrick

Publications and source records attributed to T J Kilpatrick.

At least 37 records · Page 2Linked to original sources
PubMed1999

Molecular mechanisms regulating motor neuron development and degeneration.

Motor neurons are a well-defined, although heterogeneous group of cells responsible for transmitting information from the central nervous system to the locomotor system. Spinal motor neurons are specified by soluble factors produced by structures adjacent to the primordial spinal cord, signaling through homeodomain proteins. Axonal pathfinding is regulated by cell-surface receptors that interact with extracellular ligands and once synaptic connections have formed, the survival of the somatic motor neuron is dependent on the provision of target-derived growth factors, although nontarget-derived factors, produced by either astrocytes or Schwann cells, are also potentially implicated. Somatic motor neuron degeneration leads to profound disability, and multiple pathogenetic mechanisms including aberrant growth factor signaling, abnormal neurofilament accumulation, excitotoxicity, and autoimmunity have been postulated to be responsible. Even when specific deficits have been identified, for example, mutations of the superoxide dismutase-1 gene in familial amyotrophic sclerosis and polyglutamine expansion of the androgen receptor in spinal and bulbar muscular atrophy, the mechanisms by which somatic motor neuronal degeneration occurs remain unclear. In order to treat motor system degeneration effectively, we will need to understand these mechanisms more thoroughly.

ATP-Binding Cassette Transporters↗
PubMed1999

The neurotrophins act synergistically with LIF and members of the TGF-beta superfamily to promote the survival of spiral ganglia neurons in vitro.

A number of growth factor families have been implicated in normal inner ear development, auditory neuron survival and protection. Several growth factors, including transforming growth factor-beta5 (TGF-beta5) and TGF-beta3, neurotrophin-3 (NT-3), brain-derived neurotrophic factor (BDNF) and leukemia inhibitory factor (LIF) were tested for their ability, individually or in combination, to promote auditory neuron survival in dissociated cell cultures of early rat post-natal spiral ganglion cells (SGCs). The results indicate that at discrete concentrations all growth factors act in an additive fashion and some in synergy when promoting neuronal survival. These findings support the hypothesis that growth factors from different families may be interdependent when sustaining neuronal integrity.

Animals↗
PubMed1999

Leukemia inhibitory factor is an autocrine survival factor for Schwann cells.

Schwann cells play a major role in promoting nerve survival and regeneration after injury. Their activities include providing neurotrophic factors and increasing the production of extracellular matrix components and cell surface adhesion molecules to promote axon regeneration. Following nerve transection, leukemia inhibitory factor (LIF) is up-regulated by Schwann cells at the injury site. LIF receptors are also up-regulated at the nerve injury site, but their cellular localization and function have not been fully characterized. We demonstrate that Schwann cells express mRNAs for LIF and the LIF receptor components LIF receptor subunit beta and glycoprotein 130 in vitro. We also show that although LIF is not required for the genesis of Schwann cells, it can potentiate the survival of differentiated Schwann cells in the context of neuregulin support. Not only does exogenous LIF promote survival under these conditions, but addition of the soluble LIF receptor (LIF binding protein) and anti-LIF antibodies significantly reduced cell survival, suggesting that LIF exerts autocrine effects. These results suggest that Schwann cell survival following nerve injury is potentially modulated by LIF.

Animals↗
PubMed1998

Synergy between TGF-beta 3 and NT-3 to promote the survival of spiral ganglia neurones in vitro.

Transforming growth factor-betas (TGF-betas) have been implicated in normal inner ear development and in promoting neuronal survival. Early rat post-natal spiral ganglion cells (SGC) in dissociated cell culture were used as a model of auditory innervation to test the trophic factors TGF-beta3 and neurotrophin-3 (NT-3) for their ability, individually or in combination, to promote neuronal survival. The findings from this study suggest that TGF-beta3 supports neuronal survival in a concentration-dependent manner. Moreover TGF-beta3 and NT-3-potentiated spiral ganglion neuronal survival in a synergistic fashion.

Animals↗
PubMed1998

Regulation of neural stem cell differentiation in the forebrain.

In the developing forebrain, mounting evidence suggests that neural stem cell proliferation and differentiation is regulated by growth factors. In vitro in the presence of serum, stem cell proliferation is predominantly mediated by fibroblast growth factor-2 (FGF-2) whereas neuronal differentiation can be triggered by FGF-1 in association with a specific heparan sulphate proteoglycan. On the other hand, astrocyte differentiation in vivo and in vitro appears to be dependent on signalling through the leukaemia inhibitory factor receptor (LIFR). The evidence suggests that in the absence of LIFR signalling, the stem cell population is present at approximately the same frequency and can generate neurons but is blocked from producing astrocytes that express glial fibrillary acidic protein (GFAP) or have trophic functions. The block can be overcome by other growth factors such as BMP-2/4 or interferon-gamma, providing further evidence that the inhibition to astrocyte development does not result from loss of a precursor population. Signalling through the LIFR, in addition to stimulating astrocyte differentiation, may also inhibit neuronal differentiation, which may explain why this receptor is expressed at the earliest stages of neurogenesis. Another signalling system which also exerts its influence on neurogenesis through active inhibition is Delta-Notch. We show in vitro that at high cell densities which impede neuronal production by FGF-1, lowering the levels of expression of the receptor Notch by antisense oligonucleotide results in a significant increase in neuronal production. Thus, stem cell differentiation appears to be dependent on the outcome of interactions between a number of signalling pathways, some which promote specific lineages and some which inhibit.

Animals↗
PubMed1997

LIF potentiates the NT-3-mediated survival of spiral ganglia neurones in vitro.

The survival of auditory neurones depends on the continued supply of trophic factors. Early postnatal spiral ganglion cells (SGC) in a dissociated cell culture were used as a model of auditory innervation to test the trophic factors leukaemia inhibitory factor (LIF) and neurotrophin-3 (NT-3) for their ability, individually or in combination, to promote neuronal survival. The findings suggest that LIF supports neuronal survival in a concentration-dependent manner. Moreover LIF potentiated NT-3-mediated spiral ganglion neuronal survival in a synergistic fashion.

Animals↗
PubMed1996

Increased proliferation of precursor cells in the adult rat brain after targeted lesioning.

There have been a number of reports on the proliferation of a subset of precursor cells in the subventricular zone of the lateral ventricles in the adult mammalian brain. Here we report on studies that sought to ascertain whether these cells could respond to a targeted lesion of the adult brain by increasing their proliferative rate. We have lesioned the fimbria fornix, a major pathway of septal cholinergic fibers. Previous reports demonstrated that such a lesion results in the loss of neurons in both the basal forebrain and in the CA1 field of hippocampus, without direct injury to either tissue. Ten days after making such a lesion in adult rats, the animals were given serial injections of [3H]thymidine and sacrificed after a final injection. The brains were processed for both immunocytochemistry and autoradiography. Our data demonstrate a two-fold increase over the basal proliferative rate in animals that had received such a lesion. We used a panel of antibodies to ascertain the identity of the proliferating cells. The only clearly identifiable cells that were [3H]thymidine-positive were astrocytes, based on GFAP staining. The remainder of the cells were of a null phenotype.

Animals↗
PubMed1996

Cell death in the Schwann cell lineage and its regulation by neuregulin.

The development of Schwann cells, the myelin-forming glial cells of the vertebrate peripheral nervous system, involves a neonatal phase of proliferation in which cells migrate along and segregate newly formed axons. Withdrawal from the cell cycle, around postnatal days 2-4 in rodents, initiates terminal differentiation to the myelinating state. During this time, Schwann cell number is subject to stringent regulation such that within the first postnatal week, axons and myelinating Schwann cells attain the one-to-one relationship characteristic of the mature nerve. The mechanisms that underly this developmental control remain largely undefined. In this report, we examine the role of apoptosis in the determination of postnatal Schwann cell number. We find that Schwann cells isolated from postnatal day 3 rat sciatic nerve undergo apoptosis in vitro upon serum withdrawal and that Schwann cell death can be prevented by beta forms of neuregulin (NRG-beta) but not by fibroblast growth factor 2 or platelet-derived growth factors AA and BB. This NRG-beta-mediated Schwann cell survival is apparently transduced through an ErbB2/ErbB3 receptor heterodimer. We also provide evidence that postnatal Schwann cells undergo developmentally regulated apoptosis in vivo. Together with other recent findings, these results suggest that Schwann cell apoptosis may play an important role in peripheral nerve development and that Schwann cell survival may be regulated by access to axonally derived NRG.

Animals↗
PubMed1996

Expression of the Tyro4/Mek4/Cek4 gene specifically marks a subset of embryonic motor neurons and their muscle targets.

Tyro4 is a member of the eph family of receptor protein-tyrosine kinases. We present sequence analysis that identifies Tyro4 as the rat homolog of mouse Mek4 and chick Cek4. We also present expression studies that demonstrate an evolutionarily conserved pattern of expression for Tyro4, Mek4, and Cek4. Most strikingly, we find this receptor to be specifically expressed, in all three species, in a subset of motor neurons in the medial motor column and in a subset of axial, but not limb, muscles. Mek4 has previously been ascribed a role in guiding retinal axons to their targets in the optic tectum. Our results extend the purported role of Mek4 in axon guidance to include motor neurons of the medial motor column.

Amino Acid Sequence↗
PubMed1996

Leukaemia inhibitory factor or related factors promote the differentiation of neuronal and astrocytic precursors within the developing murine spinal cord.

Previously we have shown that leukaemia inhibitory factor (LIF) potentiates the development of murine spinal cord neurons in vitro, suggesting that it, or related factors, may play an important regulatory role in neuronal development. We have further investigated this role and show here that the generation of neurons in cultures of embryonic day 10 spinal cord cells is inhibited by antibodies to the beta subunit of the LIF receptor. Since there are more undifferentiated precursors in antibody-treated cultures than in control and LIF-treated cultures, it is concluded that the primary action of LIF, or related molecules, is to promote neuronal differentiation, not precursor survival. In addition, the failure of LIF to support neuronal survival in the period immediately following differentiation suggests that the increased numbers of neurons generated with LIF are not attributable to its neurotrophic action. By selecting neuronal precursors on the basis of their inability to express class 1 major histocompatibility complex molecules, it was shown that LIF acted directly upon these cells and not via an intermediary cell. LIF also appears to be involved in regulating the differentiation of astrocytes, since it increases the number of glial fibrillary protein (GFAP)-positive cells present in the cultures and since the spontaneous production of GFAP-positive cells is blocked by antibodies to the LIF beta receptor. These findings suggest that LIF or related factors promote the differentiation of neural precursors in the spinal cord, but that they are not involved in preferentially promoting precursors down a specific differentiation pathway.

Animals↗
PubMed1995

Lineage specification of neuronal precursors in the mouse spinal cord.

We have investigated the differentiation potential of precursor cells within the developing spinal cord of mice and have shown that spinal cord cells from embryonic day 10 specifically give rise to neurons when plated onto an astrocytic monolayer, Ast-1. These neurons had the morphology of motor neurons and > 83% expressed the motor neuron markers choline acetyltransferase, peripherin, calcitonin gene-related peptide, and L-14. By comparison, < 10% of the neurons arising on monolayers of other neural cell lines or 3T3 fibroblasts had motor neuron characteristics. Cells derived from dorsal, intermediate, and ventral regions of the spinal cord all behaved similarly and gave rise to motor neuron-like cells when plated onto Ast-1. By using cells that expressed the lacZ reporter gene, it was shown that > 93% of cells present on the Ast-1 monolayers were motor neuron-like. Time-lapse analysis revealed that the precursors on the Ast-1 monolayers gave rise to neurons either directly or following a single cell division. Together, these results indicate that precursors in the murine spinal cord can be induced to differentiate into the motor neuron phenotype by factors produced by Ast-1 cells, suggesting that a similar factor(s) produced by cells akin to Ast-1 may regulate motor neuron differentiation in vivo.

Animals↗
PubMed1995

Factors regulating the differentiation of neural precursors in the forebrain.

Precursors from the neuroepithelium of the developing cortex and the adult subventricular zone can be cloned in vitro after stimulation with fibroblast growth factor 2 (FGF-2), and they have the potential to give rise to both neurons and glia. The generation of neurons from these clones can be stimulated by either a factor derived from an astrocyte precursor line, Ast-1, or FGF-1. We have shown that neuronal differentiation stimulated by FGF-1 can be inhibited by diacylglycerol lipase inhibitor and mimicked by arachidonic acid, suggesting that the neuronal differentiation is signalled through the phospholipase C gamma pathway. The sequential expression of FGF-2, followed by FGF within the developing forebrain neuroepithelium, fits with the different functions that the two FGFs play in precursor regulation. We have shown that the precursor response to FGF-1 is regulated by a heparan sulphate proteoglycan expressed within the developing neuroepithelium. Precursors restricted to the astrocyte cell lineage can be stimulated by epidermal growth factor or FGF-2F however, the differentiation into glial fibrillary acidic protein-positive astrocytes appears to require a cytokine acting through the leukaemia inhibitory factor-beta receptor.

Animals↗
PubMed1995

Regulation of neural precursor differentiation in the embryonic and adult forebrain.

1. Precursors form the neuroepithelium of the developing cortex and also from the adult sub-ventricular zone, can be cloned in vitro after stimulation with fibroblast growth factor (FGF)-2 and have the potential to give rise to both neurons and glia. The generation of neurons from these clones can be stimulated by either a factor derived from an astrocyteprecursor line, Ast-1, or FGF-1. 2. Neuronal differentiation stimulated by FGF-1 can be inhibited by diacylglycerol-lipase inhibitor and mimicked by arachidonic acid, suggesting that the neuronal differentiation is signalled through the PCL gamma pathway. 3. The sequential expression of FGF-2 and FGF-1 within the developing forebrain neuroepithelium fits with the different functions the two FGF play in precursor regulation. 4. We have shown that the precursor response to FGF-1 is regulated by a heparan sulphate proteoglycan (HSPG) expressed within the developing neuroepithelium. Precursors restricted to the astrocyte cell lineage can be stimulated by epidermal growth factor or FGF-2; however, the differentiation into GFAP positive astrocytes appears to require a cytokine acting through the leukaemia inhibitory factor beta receptor.

Adult↗
PubMed1995

Cloned multipotential precursors from the mouse cerebrum require FGF-2, whereas glial restricted precursors are stimulated with either FGF-2 or EGF.

Fibroblast growth factor-2 (FGF-2) and epidermal growth factor (EGF) have both been reported to stimulate precursors in the developing CNS. To clarify these effects, we used clonal analysis to determine the lineage potential of precursors stimulated with each factor, at two stages of development. It was found that in cells isolated from the cerebrum of embryonic day 17 (E17) mice, FGF-2 stimulated both a multipotential precursor, which gave rise to neurons and astrocytes, and a committed glial precursor. In contrast, EGF only stimulated the glial restricted precursor. Thus, it appears that the multipotential cell, previously identified to be present at E10, remains selectively responsive to FGF-2, and that the EGF responsiveness observed at E17 reflects the presence of a new restricted class of precursors, rather than a switch in factor specificity of the multipotential cell.

Animals↗
PubMed1994

The engraftment of transplanted primary neuroepithelial cells within the postnatal mouse brain.

Primary neuroepithelial precursor cells carrying the reporter gene lacZ were transplanted into postnatal murine brain and assessed for their engraftment capacity. Freshly dissected precursors, derived from lacZ transgenic embryonic day 10 mouse brain, predominantly engrafted as discrete clusters, whereas the same precursors cultured in vitro with fibroblast growth factor-2, engrafted as single cells within the parenchyma of the hippocampus. Approximately 0.5% of the transplanted cells survived in the host brain for up to 3 months. Many of these cells displayed neuronal and astrocyte morphologies. These observations suggest that transplanted primary precursors derived from the embryonic brain can engraft and commit in situ to a variety of developmental fates.

Animals↗
PubMed1994

Regulation of the early development of the nervous system by growth factors.

Development of the nervous system, although patterned by intrinsic genetic expression, appears to be dependent on growth factors for many of the differentiation steps that generate the wide variety of neurons and glia found in the both the central and peripheral nervous system. By using in vitro assays, including clonal analysis, the precise function of the various growth factors and the differentiation potential of the various neural populations has begun to be described. This review discusses some of the recent findings and examines how neuronal differentiation may result from the interaction of several growth factors.

Animals↗