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V Nurcombe

Publications and source records attributed to V Nurcombe.

7 recordsLinked to original sources
PubMed1992

Laminin in neural development.

This short and selective review of the role of laminin in neural development discusses emerging concepts about the way that elements of the extracellular matrix control the differentiation of embryonic neurons. New laminin isoforms have recently been discovered, discoveries which now reveal the very great heterology of basement membranes in different regions of the nervous system, at different stages of development. The problems of identifying true, neuronal-specific laminin receptors are also discussed, particularly with reference to neuronal pathway formation.

Animals↗
PubMed1992

MK: a pluripotential embryonic stem-cell-derived neuroregulatory factor.

MK is a gene encoding a secreted heparin-binding polypeptide originally isolated by differential screening for genes induced by retinoic acid (RA) in HM-1 embryonal carcinoma cells. Here we report that MK is expressed at high levels in both embryonal carcinoma and pluripotential embryonic stem cells and their differentiated derivatives. MK expression in these cell types is unaffected by the presence or absence of RA. Recombinant MK protein (rMK) was produced by transient expression in COS cells and purified by heparin affinity chromatography. rMK is a weak mitogen for 10T1/2 fibroblast cells but inactive as a mitogen for Swiss 3T3 fibroblasts. rMK is a potent mitogen for neurectodermal precursor cell types generated by treatment of 1009 EC cells with RA but has no mitogenic or neurotrophic effects on more mature 1009-derived neuronal cell types. rMK is active as an in vitro neurotrophic factor for E12 chick sympathetic neurons and its activity is markedly potentiated by binding the factor to tissue-culture plastic in the presence of heparin. Stable 10T1/2 cells lines have been established which express MK. These cells do not exhibit any overt evidence of cell transformation but extracellular matrix preparations derived from these cells are a potent source of MK biological activity. It is concluded that MK is a multifunctional neuroregulatory molecule whose biological activity depends upon association with components of the extracellular matrix.

Animals↗
PubMed1992

Association and release of the amyloid protein precursor of Alzheimer's disease from chick brain extracellular matrix.

The amyloid protein precursor (APP) of Alzheimer's disease was found to bind saturably (Kd = 60 nM) to embryonic chick brain extracellular matrix (ECM). The binding of APP to ECM was not inhibited by 10 micrograms/ml heparin or heparan sulfate. However, pretreatment of cells with 1 mM 4-methylumbelliferyl-beta-D-xyloside, an inhibitor of proteoglycan biosynthesis, reduced the number of APP binding sites on the ECM by 80%. The binding of APP to ECM was also inhibited by pretreatment with chlorate, an inhibitor of glycan sulfation, and heparitinase, which digests the carbohydrate component of heparan sulfate proteoglycans. These results suggest that APP binds with high affinity to one or more heparan sulfate proteoglycans. Acidic and basic fibroblasts growth factor (FGF) also bound to chick ECM. When ECM was incubated with a protease associated with the enzyme AChE (AChE-AP), APP and acidic FGF were released intact from the matrix. The AChE-AP was at least 100-fold more potent in releasing APP from ECM than other trypsin-like proteases (trypsin, plasmin, thrombin). The action of the AChE-AP was inhibited by glia-derived nexin (protease nexin I) and by human brain APP at low nanomolar concentrations. These results suggest that in vivo an AChE-AP may cleave ECM proteins to regulate the availability of soluble APP or other factors bound to the ECM.

Alzheimer Disease↗
PubMed1991

The use of the optical disector to estimate the total number of neurons in the developing chick lateral motor column: effects of purified growth factors.

Competition between neurons for limited amounts of trophic factors is believed to be the basis for large-scale neuronal death during the normal development of the vertebrate nervous system. In this study, an unbiased stereological counting method, an optical disector/Cavalieri combination, was used to estimate the total number of motor neurons in the lateral motor column of the developing chick and to assess the effects of four growth factors on neuronal numbers. The total number of neurons in lateral motor columns at embryonic day 6 (E6), E8, E10 and E12 were 18,747 +/- 1,369 (mean +/- SD), 15,037 +/- 1,816, 10,245 +/- 940, and 8,802 +/- 797, respectively. Daily exposure from E6 to E9 to three of the growth factors (basic fibroblast growth factor, bFGF; leukemia inhibitory factor, LIF; nerve growth factor, NGF) had no effect on total neuron number at E10. However, exposure to ciliary neurotrophic factor (CNTF) from E6 to E9 significantly increased (P less than 0.05) the number of neurons in the lateral motor column (13,610 +/- 725, compared with 10,058 +/- 204 in normal saline controls). These results are in agreement with previous reports of large scale neuronal death in the developing chick lumbar lateral motor column between E6 and E12 and confirm that exposure to growth factors such as CNTF can mitigate the course of normal ontogenetic cell death. The optical disector/Cavalieri combination is an efficient method for counting neurons: on average, following sectioning and staining, less than 30 min was required to estimate the total number of motor neurons in a lateral motor column with a coefficient of error of approximately 10%.

Animals↗
PubMed1991

Laminin through its long arm E8 fragment promotes the proliferation and differentiation of murine neuroepithelial cells in vitro.

The epigenetic factors involved in regulating the proliferation and differentiation of cells of the developing mammalian central nervous system are largely unknown. In this study, laminin, a molecule which is present in the basal lamina from the earliest stage of neural tube formation, has been examined in vitro for its possible regulatory role in mammalian neural development. Purified populations of murine neuroepithelial (NEP) cells isolated from the 10-day embryonic telencephalon and mesencephalon respond in vitro to laminin by undergoing aggregation, proliferation, and extensive neurite elaboration. The proliferation and differentiation of NEP cells induced by the interaction with laminin were dependent upon an early cell aggregation, since precoating of wells with poly-L-ornithine, a procedure which prevented such aggregation, completely blocked these responses. The previously reported proliferative effect of acidic fibroblast growth factor (FGF) on NEP cells was found to be synergistic with that of laminin. This observation is consistent with the idea that laminin may regulate cell responses in several ways: by direct stimulation via laminin receptors; by optimal presentation of FGF molecules to neural cells; and finally by upregulation of FGF receptor numbers on responsive cells. The in vitro response of laminin is mimicked by its long arm elastase digestion fragment, E8, whereas the cross arm fragment of laminin, E1-4, had no effect. In addition, antibodies specific for epitopes on the long arm blocked the effect seen with the whole laminin molecule. Binding studies of 125I-labeled laminin and its fragment performed on freshly isolated NEP cells confirmed the specificity of the in vitro observations: whole laminin and the E8 fragment bound to the NEP cell surface whereas the E1-4 fragment did not. These studies demonstrate mechanisms by which laminin, specifically through its long arm fragment, may assert a regulatory function during development of the mammalian central nervous system.

Animals↗
PubMed1991

Basic fibroblast growth factor upregulates steady-state levels of laminin B1 and B2 chain mRNA in cultured neuroepithelial cells.

The growth of purified populations of murine neuroepithelial cells isolated from 10 day embryonic (E10) telencephalon and mesencephalon can be specifically enhanced by supplementing growth culture media with basic fibroblast growth factor (bFGF). One effect of bFGF on cultured neuroepithelial cells was to enhance the amount of laminin expressed at the protein level as detected by immunofluorescence. This was correlated with significant upregulation of steady-state levels of laminin B1 and B2 chain expression as analyzed at the mRNA level. When E12 neuroepithelial cells were split into precursor neuronal or glial subpopulations on the basis of differential expression of major histocompatibility class-1 antigens, only the glial progenitor fraction was found to be capable of detectable laminin synthesis. It is thus possible that a primary action of FGF is to increase the synthesis and release of extracellular matrix molecules from neural cells which act back in a paracrine manner to stimulate differentiation.

Animals↗