Differentiation And Other Factors Influencing The Replication Of Murine Hepatitis Viruses In Cells From The Rat Central Nervous System

An in vitro system employing primary neural cell cultures derived from the cerebral cortices of neonatal rat brains was developed to examine, with greater fidelity, parameters influencing coronavirus (CV) induced demyelination in the rat.;Studies regarding the specificities of the viscerotropic mouse hepatitis virus MHV3 and the sero-related neurotropic JHM virus (JHMV) for neural cell types demonstrated an unambiguous tropism of {dollar}{lcub}\rm MHV\sb3{rcub}{dollar} for astrocytes and JHMV for oligodendrocytes. Relatively small changes in spatial density of oligodendrocytes profoundly influenced JHMV replication. Furthermore, repression of JHMV in oligodendrocytes was shown to be concomitant with differentiation, occurring naturally in vitro according to a \u27time clock\u27 established in vivo or by pretreatment of immature cells with inducers of differentiation that mimic or effect the activation of the adenylate cyclase system.;Examination of the cAMP-dependent protein kinases (PKI, PKII) and respective regulatory subunits (RI, RII) in primary neural cells and rat myoblasts indicated that inhibition of CV replication is correlated with the metabolism of RI. The relationship between CV replication and the adenylate cyclase system prompted an inquiry as to how early cell-virus interactions might be affected by differentiation. Effort were directed at the possibility that protein kinases and/or phosphatases, which participate in cellular regulation during differentiation, were related to CV expression. Although differentiation did not affect virus adsorption and penetration, the expression of virus-specified RNA and structural proteins was clearly impeded, implying that the block in replication occurs at the stage of uncoating. Evidence is provided suggesting that normal processing of the phosphorylated nucleocapsid (NC) protein is inhibited in differentiated oligodendrocytes.;On the basis of these data it is concluded that in vitro interaction of JHMV with oligodendrocytes accurately reflects the in vivo host control over the tropism and expression of CV. Expression of JHMV is conditional upon the state of differentiation and is interrelated with the adenylate cyclase system. Intracellular accumulation of cAMP, it seems, invokes the modulation of cellular enzymes necessary for divesting the viral genome of the NC subsequently arresting CV replication at uncoating

Kinesin Light Chains Are Essential for Axonal Transport in Drosophila

Kinesin is a heterotetramer composed of two 115-kD heavy chains and two 58-kD light chains. The microtubule motor activity of kinesin is performed by the heavy chains, but the functions of the light chains are poorly understood. Mutations were generated in the Drosophila gene Kinesin light chain (Klc), and the phenotypic consequences of loss of Klc function were analyzed at the behavioral and cellular levels. Loss of Klc function results in progressive lethargy, crawling defects, and paralysis followed by death at the end of the second larval instar. Klc mutant axons contain large aggregates of membranous organelles in segmental nerve axons. These aggregates, or organelle jams (Hurd, D.D., and W.M. Saxton. 1996. Genetics. 144: 1075-1085), contain synaptic vesicle precursors as well as organelles that may be transported by kinesin, kinesin-like protein 68D, and cytoplasmic dynein, thus providing evidence that the loss of Klc function blocks multiple pathways of axonal transport. The similarity of the Klc and Khc ((Saxton et al. Cell 64:1093-1102; Hurd, D.D., and W.M. Saxton. 1996. Genetics 144: 1075-1085) mutant phenotypes indicates that KLC is essential for kinesin function, perhaps by tethering KHC to intracellular cargos or by activating the kinesin motor