H. R. Payne

N-cadherin expression and function in cultured oligodendrocytes

N-Cadherin is a major cell adhesion molecule that is expressed in the developing nervous system where it has been implicated in neural migration and axon growth. Recently, a role for N-cadherin in oligodendrocyte differentiation has been identified [23]. Oligodendrocyte precursors adhere to N-cadherin and mature rapidly to produce myelin sheets. Since this implies that oligodendrocytes express N-cadherin, we examined the expression of N-cadherin by oligodendrocytes in culture. N-Cadherin was expressed by O-2A progenitors, immature oligodendrocytes and mature oligodendrocytes, but at a lower level than in type 1 astrocytes in the same cultures. On mature oligodendrocytes, the N-cadherin was concentrated on the major processes emerging from the soma. The ability of N-cadherin and merosin to promote oligodendrocyte precursor migration was also studied. Average migration rates were significantly higher on merosin (11.2 microns/h) than on N-cadherin (5.6 microns/h). These results suggest that N-cadherin is not likely to function predominantly as a substrate that stimulates migration of O-2A progenitors, but may be more important in initiating early oligodendrocyte-axon interactions that promote the process of myelination.

Colonic Ganglioneuromatosis in a Horse

Ganglioneuromas are complex tumors that arise in peripheral ganglia and are composed of well-differentiated neurons, nerve processes, Schwann cells, and enteric glial cells. The term ganglioneuromatosis (GN) denotes a regional or segmental proliferation of ganglioneuromatous tissue. This report describes an 8-year-old mixed breed horse with GN in a 25-cm segment of small colon. Grossly, the lesion consisted of numerous sessile to pedunculated nodules extending from the serosal surface. Histologic examination revealed the nodules to consist of fascicles of spindle-shaped cells consistent with Schwann cells, clusters of neurons, supporting enteric glial cells, and thick bands of perineurial collagen. Most of the nodules coincided with the location of the myenteric plexus and extended through the outer layer of the tunica muscularis to the serosal surface. Neuronal processes were demonstrated within the lesion with electron microscopy. With immunohistochemistry neurons were positive for neuron specific enolase (NSE) and S-100 and the Schwann cells and enteric glial cells were positive for S-100 and glial fibrillary acidic protein (GFAP). The pathogenesis of GN is poorly understood. GN, although rare, should be included in the differential diagnosis of gastrointestinal tumors in the horse.

Analysis of cell fusion induced by bovine coronavirus infection

SummaryPolykaryon formation in bovine fetal spleen (BFS) cells infected with bovine coronavirus L9 occurred only in media supplemented with trypsin. A single 1 to 2 h trypsin treatment 10 h and later after infection induced formation of polykaryons. Trypsin treatment at pH 7.5 and 8.0 induced polykaryons while treatments at lower or higher pH levels did not. Cell fusion activity was partially suppressed by the presence of antibody.

Initial events in bovine coronavirus infection: analysis through immunogold probes and lysosomotropic inhibitors.

SummaryThe early events in the infection of human rectal tumor cells by bovine coronavirus were investigated by colloidal gold-mediated immunoelectron microscopy and by analysis of the effect of lysosomotropic weak bases on virus yield. Electron microscopic studies revealed sites of fusion between the virus envelope and the plasmalemma but fusion events along intracellular membranes were not observed despite extensive searches. Virion-antibody-colloidal gold complexes were, in fact, endocytosed by synchronously infected cells. These complexes were apparently non-infectious, and they accumulated in vacuoles that resembled secondary lysosomes. Exposure of cells to ammonium chloride or to methylamine during the first hour of infection had little inhibitory effect on the production of infectious virus. Chloroquine treatments were inhibitory but this effect depended on relatively late events in the infectious process. The chloroquine inhibitory step blocked infection of virus adsorbed to cells that were exposed to buffers in the pH range of 4.4 to 8.4. These findings indicate that BCV penetrates its host cell by direct fusion with the plasmalemma and does not require an acidic intracellular compartment for infectious entry.

Hypomyelination associated with bovine viral diarrhea virus type 2 infection in a Longhorn calf.

A newborn Longhorn heifer calf presented with generalized tremors, muscle fasciculations, ataxia, and nystagmus. At necropsy, no gross central nervous system lesions were observed. Histologically, the brain and spinal cord had mild to moderate diffuse microgliosis and astrocytosis, minimal nonsuppurative encephalitis, and decreased myelin staining. Ultrastructural examination revealed thinning and absence of myelin sheaths. Various cell types were immunohistochemically positive for bovine viral diarrhea virus (BVDV). Noncytopathogenic BVDV was isolated from the brain and identified as BVDV type 2 by phylogenetic analysis. BVDV-induced hypomyelination is rare and analogous to lesions in neonates infected with border disease and classical swine fever viruses. This is the first documented case of hypomyelination in a calf specifically attributed to BVDV type 2 and the first description of the ultrastructural appearance of BVDV-induced hypomyelination.

Bovine coronavirus antigen in the host cell plasmalemma

Abstract Expression of bovine coronavirus (BCV) antigen in the plasmalemma of epithelioid human rectal tumor (HRT-18) and fibroblastic bovine fetal spleen (BFS) cell lines was traced by immunofluorescence and immunoelectron microscopy facilitated by colloidal gold. Cytoplasmic fluorescence was first observed at 12 hr postinfection (h.p.i) in infected HRT-18 cultures. This fluorescence coincided with the appearance of cell surface antigen reacting with colloidal gold-labeled antibodies to BCV antigens. At 24 h.p.i the amount of viral antigens at the surface of HRT-18 had increased, although cytoplasmic fluorescence remained constant. Infected BFS cells but not HRT-18 cells formed polykaryons when incubated in the presence of trypsin. One viral antigen in the plasma membrane of BFS cells was thus identified as the S glycoprotein with a fusion domain. In contrast to HRT-18 cells, the overall amount of BCV antigens at the surface of BFS cells remained constant after the onset of fusion. Analysis of the labeling characteristics established that the goldmarked-sites represented de novo expression of BCV antigen in the plasma membrane of infected cells.