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Biomedical subjects

A Maggs

Publications and source records attributed to A Maggs.

11 recordsLinked to original sources
PubMed1992

Myelination of regenerated axons in goldfish optic nerve by Schwann cells.

This study uses immunohistochemistry and EM to examine the site of injury in goldfish optic nerve during axonal regeneration. Within seven days of nerve crush axons begin to regrow and a network of GFAP+ reactive astrocytes appears in the nerve on either side of the injury. However, the damaged area remains GFAP-. By 42 days after nerve crush, the sheaths of new axons acquire myelin marker 6D2, and the crush area becomes populated by a mass of longitudinally-orientated S-100+ cells. Ultrastructurally, the predominant cells in the crush area bear a strong resemblance to peripheral nerve Schwann cells; they display a one-to-one association with myelinated axons, have a basal lamina and are surrounded by collagen fibres. It is proposed that these cells are Schwann cells which enter the optic nerve as a result of crush, where they become confined to the astrocyte-free crush area.

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PubMed1991

Diversity amongst the microglia in growing and regenerating fish CNS: immunohistochemical characterization using FL.1, an anti-macrophage monoclonal antibody.

We have immunohistochemically characterized the forms and distribution of microglia--the macrophages of the CNS--in fish, using a new monoclonal antibody (mAb), FL.1. This mAb specifically reacts with resident macrophages throughout the body in Oreochromine fish, including Kuppfer cells, gut-associated myeloid cells, and peritoneal macrophages, as well as with microglia, but circulating monocytes are not labelled with FL.1. The FL.1-epitope, which is lost following treatment with reducing agents, has an extracellular location and is associated with three integral membrane glycoprotein variants. FL.1-staining shows that microglia are extremely abundant throughout the fish CNS. For example, they comprise a third of the glia in the optic nerve, and 30% of all cells, including neurons, in the spinal cord, i.e., fish have about tenfold more microglia than mammals. Two forms of FL.1-positive microglia are predominant in fish, one resembling their mammalian counterparts, but less ramified, and the other comprising smaller rounded cells with very little cytoplasm, which are most numerous in the ependymal region of the optic tectum. Apart from the conventional microglia, the optic nerves also contain large lipid-laden macrophages which comprise a third form of FL.1-positive cell in the CNS. Fish optic nerves contain astrocytes of a distinct type which form reticular networks, but lack connections to capillaries (Maggs and Scholes, J. Neurosci. 1990;10:1600-1614). The co-distribution of foamy macrophages may have a metabolic role that is performed by ordinary astrocytes elsewhere in the CNS. An antiserum against the beta 2 subunit of the human leukocyte integrins (Kishimoto et al., Cell 1987a; 50:193-202) was found selectively to recognize the foamy macrophages in Oreochromis. Following lesion to the optic nerve, FL.1-labelling shows that microglia proliferate throughout the visual pathway. In the optic tectum, the additional FL.1-positive cells are concentrated in the vicinity of degenerating retinal axons and their terminals. Most of the microglia in the injured optic nerve have amoeboid morphologies, and the foamy macrophages become depleted.

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PubMed1990

Reticular astrocytes in the fish optic nerve: macroglia with epithelial characteristics form an axially repeated lacework pattern, to which nodes of Ranvier are apposed.

Astroglia in lower vertebrate optic nerves are unusual: as shown recently (Giordano et al., 1989; Rungger-Brändle et al., 1989), they express abundant Type II cytokeratin, not glial fibrillary acidic protein (GFAP), the cytoskeletal marker for astrocytes elsewhere. To determine the implications for the glial cells of these epithelial-type cytoskeletons, which are linked up by desmosomal junctions, we analyzed the tissue patterning of fish optic nerve astroglia, which we term reticular astrocytes on account of their uniquely specialized arrangement. The processes of the reticular astrocytes fasciculate extensively with one another in a pattern stabilized by the desmosomes, forming a network laid out in thin planar sheets, or partitions. These are arranged transversely, that is at right angles to the optic fibers and are repeated at regular intervals of about 15 microns longitudinally throughout the optic nerve. They merge periodically forming a 3-dimensional framework whose pattern we speculate provides a flexible tissue skeleton for the optic nerve, capable of accommodating eye movements. Virtually all fibers in mature regions of the optic nerve are myelinated, and we show that nodes of Ranvier mostly occur in register with the partitions, displaying perinodal astrocytic associations resembling those found at CNS nodes in mammals. This clustering may account for the unexpectedly high observed incidence of neighbor pairs of nodes. Among other peculiarities associated with the reticular astrocytic network, one is that up to 20% of all cells comprise foamy macrophages not found elsewhere in the CNS.

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PubMed1986

Glial domains and nerve fiber patterns in the fish retinotectal pathway.

Optic nerve fibers run parallel from the retina as far as the optic tract in fish, then suddenly criss-cross into a new pattern matching the tectal map. This change coincides with a unique demarcation between two astroglial territories in the retinotectal pathway, located where the optic chiasm occurs in other vertebrates, which we defined using antibodies directed against intermediate filaments (IF). We found that astroglia in optic nerve territory express an Mr 56,000 IF polypeptide, band 3, which we identify as the fish equivalent of vimentin in mammals. These astrocytic cells lack glial fibrillary acidic protein (GFAP; cf. Dahl and Bignami, 1973). Conversely, glia in brain territory, that is, in the optic tract and elsewhere in the CNS, lack the fish vimentin, but express GFAP. By electron microscopy, we obtained evidence that new retinal axons extend swiftly through the growing optic nerve, where they are tightly shepherded into a narrow track by newly differentiating glial cells, positive for the fish vimentin. In the GFAP-positive glial territory of the optic tract, by contrast, growing axons are slowed down and probably branch. We suggest that this allows them to fasciculate accurately with older fibers and thereby propagate a tectotopic pattern established by pioneer axons in the embryo.

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PubMed1983

The proteolytic digestion of ox neurofilaments with trypsin and alpha-chymotrypsin.

Brief digestion of ox neurofilaments with trypsin liberates fragments that are soluble and have molecular weights ranging from 164 000 to 97 000. Peptide fingerprinting indicates that these regions, termed the tryptic head-regions, arise from the 205 000- and 158 000-mol.wt. components of the triplet. The remains of the parent polypeptides sediment with normal filaments and have been termed tail-regions. Digestion of neurofilaments with chymotrypsin also liberates soluble fragments (chymotryptic head-regions) but these have mol.wts. 171 000 and 119 000, though they too originate from the higher-molecular-weight triplet polypeptides. Tryptic and chymotryptic head-regions have extensive homology, and a low (less than or equal to 20%) helix content. Electron microscopy shows that chymotryptic digestion rapidly reduces the length of filaments, probably because this enzyme preferentially attacks the 72 000-mol.wt. polypeptide. In contrast, brief digestion with trypsin does not reduce filament length even though more than 90% of the two higher-molecular-weight components have been cleaved. These results indicate that the backbone of native filaments is formed from the 72 000-mol.wt. polypeptide together with the tail-regions from the 205 000- and 158 000-mol.wt. polypeptides. The corresponding head-regions of these components, which can represent nearly 75% of each molecule, are not necessary for preserving the backbone of native neurofilaments and are therefore good candidates for being the side arms that connect these filaments in nerve cells.

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PubMed1981

The polypeptide composition of axoplasm and of neurofilaments from the marine worm Myxicola infundibulum.

1. Axoplasm from Myxicola contains two major polypeptides associated with neurofilaments, together with actin, tubulin and many minor polypeptide components. 2. Some of the minor polypeptides with molecular weights between 140,000 and 50,000 purify with neurofilaments under a variety of conditions and they appear to represent an integral part of the filament structure. 3. Peptide fingerprinting shows that the two major neurofilament polypeptides are almost identical. The fingerprint patterns from these major polypeptides share features with those obtained from the minor components. 4. Peptide fingerprinting has enabled us to propose a scheme for the main sites at which papain cleaves the major neurofilament polypeptides. In addition fingerprinting indicates how the minor components are related to the major polypeptides. 5. It is suggested that many of the minor neurofilament polypeptides could arise by proteolysis in vivo.

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PubMed1981

The location of phosphorylation sites and Ca2+-dependent proteolytic cleavage sites on the major neurofilament polypeptides from Myxicola infundibulum.

1. When axoplasm is incubated with [32P]Pi the main phosphorylated components are the neurofilament polypeptides. 2. Activation with Ca2+ of the proteinase present in axoplasm causes degradation of these neurofilaments and the peptides produced by this reaction have been analysed by fingerprinting. 3. Fingerprinting shows that initially the Ca2+-activated proteinase cleaves the neurofilament polypeptides at three major sites producing polypeptides with mol.wts. 70,000, 50,000 and 47,000. 4. These polypeptides sediment with filaments, originate from the tail-region of the molecule and contain a little radioactive label. 5. As these polypeptides are produced, other polypeptides that come from the head-region of the molecule are liberated as soluble products that contain the bulk of the radioactivity. 6. Fingerprinting therefore shows that at least two regions on the molecule are phosphorylated and that the major one is located towards the head-end of the polypeptides.

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