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M C Raff

Publications and source records attributed to M C Raff.

At least 91 records · Page 5Linked to original sources
PubMed1988

Differentiation of a bipotential glial progenitor cell: what controls the timing and the choice of developmental pathway?

In the rat central nervous system (CNS) oligodendrocytes and type-2 astrocytes are thought to develop from a common precursor - the O-2A progenitor cell. Oligodendrocytes develop first and make myelin; type-2 astrocytes develop later and extend processes to nodes of Ranvier. The timing of differentiation of O-2A progenitor cells seems to depend on chemical signals secreted by another type of glial cell - the type-1 astrocyte. Type-1 astrocytes secrete platelet-derived growth factor (PDGF), which stimulates O-2A progenitor cell proliferation and drives the clock that controls the onset of oligodendrocyte differentiation, which is the constitutive pathway of progenitor cell development. Later, type-1 astrocytes are thought to secrete a CNTF-like protein that initiates type-2 astrocyte differentiation.

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PubMed1987

Glial cells in the rat optic nerve and some thoughts on remyelination in the mammalian CNS.

Studies on the rat optic nerve in the past 5 years have produced two surprises. First, they demonstrated that there are two biochemically, developmentally and functionally distinct types of astrocytes in the optic nerve, and probably in white matter tracts throughout the CNS: one seems to be responsible for inducing endothelial cells to form the blood-brain barrier while the other seems to service nodes of Ranvier. Second, they showed that oligodendrocytes and type-2 astrocytes develop from a common bipotential (O-2A) progenitor cell that seems to migrate into the developing optic nerve, and may well migrate all over the CNS to wherever myelination is required; this implies that the neuroepithelial cells of the optic stalk are restricted to forming type-1 astrocytes. Some of the findings in the optic nerve may be relevant to the problem of CNS regeneration after injury. These include the following. (1) Reactive gliosis in white matter tracts seems to be mainly a function of type-1 astrocytes. (2) Proliferating O-2A progenitor cells are present in the adult CNS, raising the possibility that they may be able to produce new oligodendrocytes and type-2 astrocytes following injury and thereby aid regeneration. (3) Type-1 astrocytes seem to be able to respond to environmental signals and form localized barriers that block the migration of O-2A progenitor cells; it is conceivable that the same barriers block the migration of regenerating axonal growth cones.

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PubMed1987

Voltage gated ionic channels in rat cultured astrocytes, reactive astrocytes and an astrocyte-oligodendrocyte progenitor cell.

Astrocytes (both type 1 and type 2), cultured from the central nervous system of newborn or 7 day old rats show voltage gated sodium and potassium channels that are activated when the membrane is depolarized to greater than -40 mV. The sodium channels in these cells have an h-infinity curve similar to that of nodal membranes but the activation (peak current-voltage) curves are shifted along the voltage axis by about +30 mV. These sodium currents are blocked only by high concentrations of tetrodotoxin. The voltage activated potassium currents in both types of astrocyte show at least two components; an inactivating component that is suppressed at holding potentials of greater than -40 mV and a persistent, non-inactivating current. Several types of single channel currents were observed in outside-out membrane patches from type 2 astrocytes. One type of potassium channel showed inactivation on depolarization and may contribute to the whole-cell inactivating current. In contrast, oligodendrocytes showed no obvious voltage gated membrane channels. The properties of the type 2 astrocyte-oligodendrocyte progenitor cell were investigated in two ways: 1) by examination of cells just beginning to differentiate along the "electrically silent" oligodendrocyte pathway or 2) by recording from progenitor cells cultured for 24 hours in the presence of cycloheximide to block the appearance of new membrane channels. In both cases, voltage gated inward (sodium) and outward (potassium) currents were noted. The outward current response showed both an inactivating and a non-inactivating component. Similar voltage activated inward and outward membrane currents were noted in reactive astrocytes freshly isolated (3-6 hours) from lesioned areas of adult rat brains.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1987

An inducer protein may control the timing of fate switching in a bipotential glial progenitor cell in rat optic nerve.

In rat optic nerve, oligodendrocytes and type-2 astrocytes develop from a common (O-2A) progenitor cell. The first oligodendrocytes differentiate at birth, while the first type-2 astrocytes differentiate in the second postnatal week. We previously showed that the timing of oligodendrocyte differentiation depends on an intrinsic clock in the O-2A progenitor cell. Here we provide evidence that the timing of type-2 astrocyte differentiation, by contrast, may depend on an inducing protein that appears late in the developing nerve. We show that extracts of 3- to 4-week-old, but not 1-week-old, rat optic nerve contain a protein (apparent Mr approximately 25,000) that induces O-2A progenitor cells in culture to express glial fibrillary acidic protein (GFAP), an astrocyte-specific marker in the rat central nervous system.

Age Factors↗
PubMed1986

Clonal analysis of oligodendrocyte development in culture: evidence for a developmental clock that counts cell divisions.

The clonal development of oligodendrocytes was studied by culturing individual oligodendrocyte--type-2 astrocyte (O-2A) progenitor cells on monolayers of type-1 astrocytes, which stimulate O-2A progenitor cells to divide. Oligodendrocytes developed by a proliferative lineage in which clonal progeny differentiated together after a number of cell divisions. Most O-2A progenitor cells had similar cell cycle times (1-2 days), but their proliferative capacity varied greatly: some divided only once while others divided up to eight times before differentiating. sister cells behaved similarly when recultured separately on astrocyte monolayers. These findings are consistent with the cell-division-counting hypothesis previously proposed to explain the timing of oligodendrocyte differentiation. They also unambiguously establish the phenotype of O-2A progenitor cells in vitro and demonstrate that these cells respond directly to growth factors produced by type-1 astrocyte monolayers.

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PubMed1986

Molecular specialization of astrocyte processes at nodes of Ranvier in rat optic nerve.

The HNK-1 and L2 monoclonal antibodies are thought to recognize identical or closely associated carbohydrate epitopes on a family of neural plasma membrane glycoproteins, including myelin-associated glycoprotein, the neural cell adhesion molecule, and the L1 and J1 glycoproteins, all of which have been postulated to play a part in mediating cell-cell interactions in the nervous system. We have used these two antibodies in immunofluorescence and immunogold-electron microscopic studies of semithin and ultrathin frozen sections of adult rat optic nerve, respectively, and we show that they bind mainly to astrocyte processes around nodes of Ranvier. Most other elements of the nerve, including astrocyte cell bodies and large astrocytic processes, are not labeled by the antibodies. To our knowledge, this is the first demonstration that perinodal astrocyte processes are biochemically specialized. We provide evidence that one of the HNK-1+/L2+ molecules concentrated around perinodal astrocyte processes is the J1 glycoprotein; our findings, taken together with previously reported observations, suggest that the other known HNK-1+/L2+ molecules are not concentrated on these processes. Since anti-J1 antibodies previously have been shown to inhibit neuron to astrocyte adhesion in vitro, we hypothesize that J1 may play an important part in the axon-glial interactions that presumably are involved in the assembly and/or maintenance of nodes of Ranvier.

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PubMed1986

Is reactive gliosis a property of a distinct subpopulation of astrocytes?

We have shown previously that the A2B5 monoclonal antibody distinguishes two types of glial fibrillary acidic protein-containing astrocytes in semithin frozen sections of adult rat optic nerve: A2B5- (type-1) astrocytes are found mainly at the periphery of the nerve, where they form the glial limiting membrane, while A2B5+ (type-2) astrocytes are found mainly in the interior of the nerve and constitute more than 65% of the astrocytes in the adult optic nerve. In the present study we show that although most astrocytes in semithin frozen sections of adult rat corpus callosum and optic nerve are A2B5+, the great majority of reactive astrocytes in similar sections of corpus callosum examined 20 weeks after a stab lesion, and in optic nerve examined 20 weeks after adult transection, are A2B5-. Although both A2B5+ and A2B5- astrocytes are stimulated to synthesize DNA in the first week after transection, adult optic nerves examined 20 weeks after transection contain only half as many astrocytes as do normal optic nerves: While A2B5+ astrocytes are reduced almost 10-fold, A2B5- astrocytes are increased by about 25%. We consider the simplest interpretation of these findings to be that type-1 astrocytes are largely responsible for forming glial scars in adult white matter following either a stab lesion or Wallerian degeneration and that in transected optic nerves, most type-2 astrocytes eventually die, possibly because they depend on axons for their long-term survival.

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PubMed1985

Macroglial cell development in embryonic rat brain: studies using monoclonal antibodies, fluorescence activated cell sorting, and cell culture.

Astrocytes, ependymal cells, and oligodendrocytes have been shown to develop on the same schedule in dissociated cell cultures of early embryonic rat brain as in vivo. Subsequent studies showed that there are two major types of astrocyte (type-1 and type-2), which, in cultures of perinatal optic nerve, develop as two distinct lineages. In such cultures, type-2 astrocytes and oligodendrocytes develop from the same, bipotential, (O-2A) progenitor cells, which differentiate into type-2 astrocytes in 10% fetal calf serum (FCS) and into oligodendrocytes in less than or equal to 0.5% FCS. In light of these findings, we now have extended our studies on macroglial cell development in rat brain and show the following: (i) The first astrocytes to develop have a type-1 phenotype, while astrocytes with a type-2 phenotype do not develop until almost 2 weeks later, just as in the optic nerve. (ii) Most importantly, type-2 astrocytes, like the other macroglial cells, develop on the same schedule in cultures of early embryonic (less than or equal to E15) brain as they do in vivo. (iii) By contrast, both oligodendrocytes and type-2 astrocytes develop prematurely in cultures of E17 brain, and FCS influences this development in the same way it does in perinatal optic nerve cultures. (iv) Type-2 astrocyte precursors are labeled by the A2B5 monoclonal antibody, as shown previously for oligodendrocyte precursors in brain and for O-2A progenitor cells in optic nerve. Taken together with our previous findings, these results suggest that oligodendrocytes and type-2 astrocytes in brain develop from bipotential O-2A progenitor cells, whose choice of developmental pathway and timing of differentiation depend on mechanisms that operate independently of brain morphogenesis.

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PubMed1985

A quantitative immunohistochemical study of macroglial cell development in the rat optic nerve: in vivo evidence for two distinct astrocyte lineages.

We have shown previously that three antibodies--anti-galactocerebroside (GC), anti-glial fibrillary acidic protein (GFAP), and the A2B5 monoclonal antibody--can be used to help distinguish three classes of glial cells in the rat optic nerve: oligodendrocytes are GC+, GFAP-, almost all type-1 astrocytes are A2B5-, GFAP+, and almost all type-2 astrocytes are A2B5+, GFAP+. In the present study we have used these antibodies to examine the timing and sequence of the development of the three types of glial cells in vivo. We show that type-1 astrocytes first appear at embryonic Day 16 (E16), oligodendrocytes at birth (E21), and type-2 astrocytes between postnatal Days 7 and 10 (P7-10). Moreover, we demonstrate quantitatively that astrocytes in the optic nerve develop in two waves, with more than 95% of type-1 astrocytes developing before P15 and more than 95% of type-2 astrocytes developing after P15. Finally, we provide indirect evidence that type-2 astrocytes do not develop from type-1 astrocytes in vivo, supporting previous direct evidence that the two types of astrocytes develop from two serologically distinct precursor cells in vitro.

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PubMed1985

Reconstitution of a developmental clock in vitro: a critical role for astrocytes in the timing of oligodendrocyte differentiation.

The rat optic nerve contains three types of macroglial cells: type 1 astrocytes first appear at embryonic day 16 (E16), oligodendrocytes at birth (E21), and type 2 astrocytes between postnatal days 7 and 10. The oligodendrocytes and type 2 astrocytes develop from a common, bipotential O-2A progenitor cell. We show here that although O-2A progenitor cells in E17 optic nerve prematurely stop dividing and differentiate into oligodendrocytes within 2 days in culture, when cultured on a monolayer of type 1 astrocytes, they continue to proliferate; moreover, the first cells differentiate into oligodendrocytes after 4 days in vitro, which is equivalent to the time that oligodendrocytes first appear in vivo. Our findings suggest that the timing of oligodendrocyte differentiation depends on an intrinsic clock in the O-2A progenitor cell that counts cell divisions that are driven by a growth factor (or factors) produced by type 1 astrocytes.

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PubMed1984

The in vitro differentiation of a bipotential glial progenitor cell.

We have studied the properties of a glial progenitor cell from 7-day-old rat optic nerve that differentiates in vitro into an oligodendrocyte if cultured in serum-free medium and into an astrocyte if cultured in foetal calf serum (FCS). Using galactocerebroside as a marker of oligodendrocyte differentiation and glial fibrillary acidic protein as a marker of astrocyte differentiation, we show that the acquisition of these marker molecules occurs rapidly in culture and requires both RNA and protein synthesis. We provide evidence that the effect of FCS on the development of the glial progenitor cell is not due to its influence on cell-substrate adherence or actin filament organization and is not mimicked by an increase in intracellular cyclic AMP, cyclic GMP or pH. The progenitor cell contains vimentin filaments and retains them on becoming an astrocyte but loses them on becoming an oligodendrocyte. Most importantly, we show that the choice of developmental pathway taken by the bipotential glial progenitor cells in culture is reversible for 1-2 days and then becomes fixed, at least under the conditions we studied.

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PubMed1984

A4: an antigenic marker of neural tube-derived cells.

The A4 monoclonal antibody was originally found to bind to the surface of the majority of neurons in rat CNS cultures, but not to PNS neurons or non-neural cells. It was subsequently shown to bind to immature oligodendrocytes and their precursor cells but not to the most mature oligodendrocytes. In the present study, we have used immunofluorescence assays on cell suspensions and cultures and on semi-thin, frozen tissue sections to show that protoplasmic and fibrous astrocytes and most ependymal cells are also A4+. Taken together, these results suggest that in adult rats A4 is expressed exclusively by cells of the CNS and that all cell types derived from the neural tube are A4+, at least at some time in their development. While neurons, astrocytes and ependymal cells continue to express the antigen in adults, most oligodendrocytes appear to lose it as they mature. The finding that macrophages in CNS cell suspensions and cultures are A4- suggests that microglial cells are not derived from the neural tube.

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PubMed1984

Effects of neonatal transection on glial cell development in the rat optic nerve: evidence that the oligodendrocyte-type 2 astrocyte cell lineage depends on axons for its survival.

We have previously provided evidence that the rat optic nerve contains three types of macroglial cells that develop as two distinct lineages: one lineage comprises type 1 astrocytes, which develop before birth, while the other comprises oligodendrocytes and type 2 astrocytes, which develop after birth from a common, bipotential glial progenitor cell. In the present study we have examined the influence of axons on the development of these two glial cell lineages by cutting the optic nerve at birth so that the retinal ganglion cell axons in the nerve degenerate. Using antibodies to distinguish the different types of glial cells in suspensions and semithin frozen sections of cut and uncut optic nerves, we show that neonatal transection results in a striking decrease in the total number of oligodendrocytes, type 2 astrocytes and their progenitor cells but has much less effect on the number of type 1 astrocytes. Since the [3H]thymidine labelling indices of oligodendrocytes and their progenitor cells were not significantly decreased in cut nerves, our results suggest that the progenitor cells and/or their progeny die in large numbers following neonatal nerve transection. We conclude that axons are required for the survival of cells of the oligodendrocyte-type 2 astrocyte lineage, at least during postnatal development.

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PubMed1984

Two glial cell lineages diverge prenatally in rat optic nerve.

Three types of glial cells have been previously described in cultures of neonatal rat optic nerve--oligodendrocytes, type 1 astrocytes, and type 2 astrocytes--which can be distinguished using three different antibodies: antigalactocerebroside antibodies recognize oligodendrocytes; antibodies against glial fibrillary acidic protein recognize both types of astrocytes, while the A2B5 monoclonal antibody distinguishes between the two, binding to type 2 but not type 1 astrocytes. It was subsequently shown that oligodendrocytes and type 2 astrocytes, but not type 1 astrocytes, develop in cultures of 7 day optic nerve from a common, A2B5+ progenitor cell. In the present study, the distribution of rat neural antigen-2 (Ran-2), a cell-surface antigen defined by a monoclonal antibody, has been examined on optic nerve cells. It is demonstrated that, in contrast to A2B5, Ran-2 is present on type 1 but not type 2 astrocytes in optic nerve cultures. More importantly, it is shown that Ran-2 and A2B5 antibodies react with largely nonoverlapping populations of cells in cell suspensions of embryonic Day 17 (E17) and postnatal Day 1 (P1) optic nerve, and that the Ran-2+, A2B5- population contains type 1 astrocytes and their precursors while the A2B5+,Ran-2- population contains the progenitor cells for oligodendrocytes and type 2 astrocytes. These findings provide strong evidence that the glial cells of the rat optic nerve develop as two distinct lineages--one giving rise to type 1 astrocytes and the other to oligodendrocytes and type 2 astrocytes--and that the two lineages diverge as early as E17.

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PubMed1984

Fibrous and protoplasmic astrocytes are biochemically and developmentally distinct.

We have studied semithin frozen sections of developing and adult rat central nervous system (CNS) by indirect immunofluorescence in order to determine the antigenic phenotype of protoplasmic and fibrous astrocytes. Using antibodies against glial fibrillary acidic protein (GFAP) to identify astrocytes, we show that the great majority of fibrous astrocytes in adult optic nerve are labeled by the monoclonal antibody A2B5, while the great majority of protoplasmic astrocytes in adult cerebral cortex are not. Astrocytes located at the periphery of the adult optic nerve that form the glial limiting membrane are more like protoplasmic astrocytes than fibrous astrocytes in that they strain relatively weakly with anti-GFAP antiserum and are A2B5-. In the developing rat optic nerve, protoplasmic-like astrocytes appear at least one week before the first fibrous astrocytes can be detected. Taken together with our previous observations on astrocytes in suspensions and cultures of developing rat optic nerve (Raff, M.C., E.R. Abney, J. Cohen, R. Lindsay, and M. Noble (1983) J. Neurosci. 3: 1289-1300; Raff, M.C., R.H. Miller, and M. Noble (1983) Nature 303: 390-396), these results suggest that protoplasmic and fibrous astrocytes are distinct classes of glial cells that differ in their antigenic phenotype and developmental history, as well as in their morphology and location within the CNS.

Aging↗
PubMed1983

Tracing the development of oligodendrocytes from precursor cells using monoclonal antibodies, fluorescence-activated cell sorting, and cell culture.

We have used antibody and complement-mediated cell killing, fluorescence-activated cell sorting and tissue culture to study the development of rat oligodendrocytes. We show that (1) three ligands that bind to the majority of CNS neurons (the monoclonal antibodies A4 and A2B5 and tetanus toxin) also bind to immature oligodendrocytes and to precursor cells in 14-day embryonic rat brain that develop into oligodendrocytes in vitro; and (2) precursor cells in 17- to 18-day embryonic rat optic nerve can develop into oligodendrocytes in vitro in the absence of living neurons.

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