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M C Raff

Publications and source records attributed to M C Raff.

At least 73 records · Page 4Linked to original sources
PubMed1991

Regional distribution, developmental changes, and cellular localization of CNTF-mRNA and protein in the rat brain.

Ciliary neurotrophic factor (CNTF) is a potent survival molecule for a variety of embryonic neurons in culture. The developmental expression of CNTF occurs clearly after the time period of the physiological cell death of CNTF-responsive neurons. This, together with the sites of expression, excludes CNTF as a target-derived neuronal survival factor, at least in rodents. However, CNTF also participates in the induction of type 2 astrocyte differentiation in vitro. Here we demonstrate that the time course of the expression of CNTF-mRNA and protein in the rat optic nerve (as evaluated by quantitative Northern blot analysis and biological activity, respectively) is compatible with such a glial differentiation function of CNTF in vivo. We also show that the type 2 astrocyte-inducing activity previously demonstrated in optic nerve extract can be precipitated by an antiserum against CNTF. Immunohistochemical analysis of astrocytes in vitro and in vivo demonstrates that the expression of CNTF is confined to a subpopulation of type 1 astrocytes. The olfactory bulb of adult rats has comparably high levels of CNTF to the optic nerve, and here again, CNTF-immunoreactivity is localized in a subpopulation of astrocytes. However, the postnatal expression of CNTF in the olfactory bulb occurs later than in the optic nerve. In other brain regions both CNTF-mRNA and protein levels are much lower.

Amino Acid Sequence↗
PubMed1990

Rod photoreceptor development in vitro: intrinsic properties of proliferating neuroepithelial cells change as development proceeds in the rat retina.

We describe a reaggregated cell culture system in which retinal neuroepithelial cells from embryonic rats proliferate extensively and give rise to rod photoreceptors on the same schedule in vitro as they do in vivo. Both the proliferative potential of the embryonic neuroepithelial cells and the timing of their differentiation into rods are not changed by the presence of a 50-fold excess of neonatal neural retinal cells, although many more of the embryonic cells develop into rods in these circumstances. In such mixed-age cultures, dividing neonatal cells proliferate much less and give rise to rods much sooner than do dividing embryonic cells, suggesting that the dividing cells at the two ages are intrinsically different. These and other findings suggest that both cell-cell interactions and an intrinsic program in neuroepithelial cells determine cell fate in the developing rat retina.

Aging↗
PubMed1990

Analysis of the cell-cell interactions that control type-2 astrocyte development in vitro.

Oligodendrocytes and type-2 astrocytes develop sequentially from O-2A progenitor cells in the rat CNS. We have reproduced this sequential development in a simplified, serum-free in vitro system: in cultures of newborn optic nerve cells treated with platelet-derived growth factor to maintain O-2A progenitor cell proliferation, progenitor cells differentiate into oligodendrocytes during the first week in vitro and into type-2 astrocytes during the second week. Thus all of the signals needed for type-2 astrocyte development are made by serum-free optic nerve cultures, indicating that neurons are not required. By manipulating the cellular composition of the cultures, we provide evidence that type-2 astrocyte development does not depend on oligodendrocytes, but instead requires non-O-2A lineage cells, which are also responsible for timing this development.

Animals↗
PubMed1990

Extracellular matrix-associated molecules collaborate with ciliary neurotrophic factor to induce type-2 astrocyte development.

O-2A progenitor cells give rise to both oligodendrocytes and type-2 astrocytes in vitro. Whereas oligodendrocyte differentiation occurs constitutively, type-2 astrocyte differentiation requires extracellular signals, one of which is thought to be ciliary neurotrophic factor (CNTF). CNTF, however, is insufficient by itself to induce the development of stable type-2 astrocytes. In this report we show the following: (a) that molecules associated with the extracellular matrix (ECM) cooperate with CNTF to induce stable type-2 astrocyte differentiation in serum-free cultures. The combination of CNTF and the ECM-associated molecules thus mimics the effect of FCS, which has been shown previously to induce stable type-2 astrocyte differentiation in vitro. (b) Both the ECM-associated molecules and CNTF act directly on O-2A progenitor cells and can induce them to differentiate prematurely into type-2 astrocytes. (c) ECM-associated molecules also inhibit oligodendrocyte differentiation, even in the absence of CNTF, but this inhibition is not sufficient on its own to induce type-2 astrocyte differentiation. (d) Whereas the effect of ECM on oligodendrocyte differentiation is mimicked by basic fibroblast growth factor (bFGF), the effect of ECM on type-2 astrocyte differentiation is not. (e) The ECM-associated molecules that are responsible for inhibiting oligodendrocyte differentiation and for cooperating with CNTF to induce type-2 astrocyte differentiation are made by non-glial cells in vitro. (f) Molecules that have these activities and bind to ECM are present in the optic nerve at the time type-2 astrocytes are thought to be developing.

Animals↗
PubMed1989

Glial cell diversification in the rat optic nerve.

A central challenge in developmental neurobiology is to understand how an apparently homogeneous population of neuroepithelial cells in the early mammalian embryo gives rise to the great diversity of nerve cells (neurons) and supporting cells (glial cells) in the mature central nervous system. Because the optic nerve is one of the several types of glial cells but no intrinsic neurons, it is an attractive place to investigate how neuroepithelial cells diversify. Studies of developing rat optic nerve cells in culture suggest that both cell-cell interactions and intrinsic cellular programs play important parts in glial cell diversification.

Animals↗
PubMed1989

Subpial and perivascular astrocytes associated with nodes of Ranvier in the rat optic nerve.

Recent evidence has suggested that there is a division of labour between two types of astrocytes in the rat optic nerve--one type extending processes to the pial surface and to blood vessels, the other extending processes to nodes of Ranvier (Miller et al., 1989b). Here we show that astrocytes and astrocyte processes located at the pial surface and around blood vessels in the rat optic nerve can also be associated with nodes of Ranvier, indicating that the division of labour between the two types of astrocytes in the nerve is not as strict as previously proposed.

Animals↗
PubMed1989

PDGF and intracellular signaling in the timing of oligodendrocyte differentiation.

In the rat optic nerve, bipotential O-2A progenitor cells give rise to oligodendrocytes and type 2 astrocytes on a precise schedule. Previous studies suggest that PDGF plays an important part in timing oligodendrocyte development by stimulating O-2A progenitor cells to proliferate until they become mitotically unresponsive to PDGF, stop dividing, and differentiate automatically into oligodendrocytes. Since the loss of mitotic responsiveness to PDGF has been shown not to be due to a loss of PDGF receptors, we have now examined the possibility that the unresponsiveness results from an uncoupling of these receptors from early intracellular signaling pathways. We show that (a) although PDGF does not stimulate newly formed oligodendrocytes to synthesize DNA, it induces an increase in cytosolic Ca2+ in these cells; (b) a combination of a Ca2+ ionophore plus a phorbol ester mimics the effect of PDGF, both in stimulating O-2A progenitor cell division and in reconstituting the normal timing of oligodendrocyte differentiation in culture; and (c) the same combination of drugs does not stimulate newly formed oligodendrocytes to proliferate, even in the presence of PDGF or dibutyryl cAMP. The most parsimonious explanation for these results is that O-2A progenitor cells become mitotically unresponsive to PDGF because the intracellular signaling pathways from the PDGF receptor to the nucleus are blocked downstream from the receptor and some of the early events that are triggered by receptor activation.

Animals↗
PubMed1989

PDGF receptors on cells of the oligodendrocyte-type-2 astrocyte (O-2A) cell lineage.

It has been shown previously that cultures of rat optic nerve contain three types of macroglial cells--oligodendrocytes and two types of astrocytes. Type-1 astrocytes develop from their own precursor cells beginning before birth, while oligodendrocytes and type-2 astrocytes develop postnatally from a common bipotential precursor called the O-2A progenitor cell. Proliferating O-2A progenitor cells give rise to postmitotic oligodendrocytes beginning around birth, and to type-2 astrocytes beginning in the second postnatal week. Studies in vitro have suggested that platelet-derived growth factor (PDGF), secreted by type-1 astrocytes, plays an important part in timing oligodendrocyte development: PDGF seems to keep O-2A progenitor cells proliferating until an intrinsic clock in the progenitor cells initiates the process leading to oligodendrocyte differentiation. The clock apparently determines when a progenitor cell becomes unresponsive to PDGF, at which point the cell stops dividing and, as a consequence, automatically differentiates into an oligodendrocyte. Here we have used radiolabelled PDGF to show that O-2A progenitor cells have PDGF receptors, suggesting that these cells respond directly to PDGF. The receptors resemble the type A PDGF receptor previously described on human fibroblasts and are initially retained when progenitor cells stop dividing and develop in vitro into oligodendrocytes. The latter finding indicates that receptor loss is not the reason that progenitor cells initially become mitotically unresponsive to PDGF.

Animals↗
PubMed1988

Ciliary neurotrophic factor induces type-2 astrocyte differentiation in culture.

We have been studying a population of bipotential glial progenitor cells in the perinatal rat optic nerve and brain in an attempt to understand how cells choose between alternative fates in the developing mammalian central nervous system (CNS). This cell population gives rise initially to oligodendrocytes and then to type-2 astrocytes, both of which apparently collaborate in sheathing axons in the CNS. In vitro studies suggest that oligodendrocyte differentiation is the constitutive pathway of development for the oligodendrocyte-type-2-astrocyte (O-2A) progenitor cell, whereas type-2 astrocyte differentiation depends on a specific inducing protein. This protein is present in the developing optic nerve when type-2 astrocytes are differentiating and can induce O-2A progenitor cells in vitro to express glial fibrillary acidic protein (GFAP), a marker of astrocyte differentiation. Here we show that the type-2-astrocyte-inducing protein is similar or identical to ciliary neutrotrophic factor (CNTF), which promotes the survival of some types of peripheral neurons in vitro, including ciliary ganglion neurons. This suggests that CNTF, in addition to its effect on neurons, may be responsible for triggering type-2 astrocyte differentiation in the developing CNS.

Animals↗
PubMed1988

Platelet-derived growth factor from astrocytes drives the clock that times oligodendrocyte development in culture.

The various cell types in a multicellular animal differentiate on a predictable schedule but the mechanisms responsible for timing cell differentiation are largely unknown. We have studied a population of bipotential glial (O-2A) progenitor cells in the developing rat optic nerve that gives rise to oligodendrocytes beginning at birth and to type-2 astrocytes beginning in the second postnatal week. Whereas, in vivo, these O-2A progenitor cells proliferate and give rise to postimitotic oligodendrocytes over several weeks, in serum-free (or low-serum) culture they stop dividing prematurely and differentiate into oligodendrocytes within two or three days. The normal timing of oligodendrocyte development can be restored if embryonic optic-nerve cells are cultured in medium conditioned by type-1 astrocytes, the first glial cells to differentiate in the nerve: in this case the progenitor cells continue to proliferate, the first oligodendrocytes appear on the equivalent of the day of birth, and new oligodendrocytes continue to develop over several weeks, just as in vivo. Here we show that platelet-derived growth factor (PDGF) can replace type-1-astrocyte-conditioned medium in restoring the normal timing of oligodendrocyte differentiation in vitro and that anti-PDGF antibodies inhibit this property of the appropriately conditioned medium. We also show that PDGF is present in the developing optic nerve. These findings suggest that type-1-astrocyte-derived PDGF drives the clock that times oligodendrocyte development.

Animals↗
PubMed1988

Retinal astrocytes are immigrants from the optic nerve.

The retina in most mammals contains two types of macroglial cells--Müller cells, which span the entire thickness of the retina, and astrocytes, which are mainly confined to the nerve fibre layer. Whereas Müller cells are diffusely distributed in all vertebrate retinae, the presence and distribution of retinal astrocytes correlate with the presence and distribution of retinal blood vessels: retinae that are avascular contain no astrocytes; those that are diffusely vascularized contain diffusely distributed astrocytes; and those that are vascularized in a restricted region contain astrocytes only in the vascularized region. This striking correlation between vascularization and the presence of astrocytes led Stone and Dreher to postulate that retinal astrocytes are immigrants that enter the retina with its vasculature, although others have suggested that they derive from Müller cells. Here we provide strong evidence that astrocytes in the diffusely vascularized rat retina are immigrants from the optic nerve.

Animals↗
PubMed1988

Evidence that migratory oligodendrocyte-type-2 astrocyte (O-2A) progenitor cells are kept out of the rat retina by a barrier at the eye-end of the optic nerve.

There is evidence that oligodendrocyte-type-2 astrocyte (O-2A) progenitor cells migrate along the developing rat optic nerve from the chiasm toward the eye before differentiating into oligodendrocytes that myelinate the retinal ganglion cell axons in the nerve. Why, then, do these progenitor cells not migrate into the eye, differentiate into oligodendrocytes and myelinate the nerve fibre layer of the retina? Myelination would opacify the neural retina and thereby severely impair vision. Here we provide evidence that there is a barrier at the eye-end of the rat optic nerve that prevents the migration of O-2A progenitor cells into the retina. Our findings in the rat support a previous hypothesis that such a barrier keeps myelin-forming glial cells out of the human retina.

Animals↗
PubMed1988

Type-2 astrocyte development in rat brain cultures is initiated by a CNTF-like protein produced by type-1 astrocytes.

O-2A progenitor cells are bipotential glial precursors that give rise to both oligodendrocytes and type-2 astrocytes on a precise schedule in the rat CNS. Studies in culture suggest that oligodendrocyte differentiation occurs constitutively, while type-2 astrocyte differentiation requires an exogenous inducer such as fetal calf serum. Here we describe a rat brain cell culture system in which type-2 astrocytes develop on schedule in the absence of exogenous inducers. Coincident with type-2-astrocyte development, the cultures produce an approximately 20 kd type-2-astrocyte-inducing factor(s). Purified cultures of type-1 astrocytes can produce a similar factor(s). Under conditions where they produce type-2-astrocyte-inducing factor(s), both brain and type-1 astrocyte cultures produce a factor(s) with ciliary neurotrophic (CNTF)-like activity. Purified CNTF, like the inducers from brain and type-1 astrocyte cultures, prematurely induces type-2 astrocyte differentiation in brain cultures. These findings suggest that type-2 astrocyte development is initiated by a CNTF-like protein produced by type-1 astrocytes.

Aging↗