Morphological changes in BHK-21 cells infected with S-N (H2N1) influenza virus

The Role of Lamins in the Nucleoplasmic Reticulum, a Pleiomorphic Organelle That Enhances Nucleo-Cytoplasmic Interplay

Invaginations of the nuclear membrane occur in different shapes, sizes, and compositions. Part of these pleiomorphic invaginations make up the nucleoplasmic reticulum (NR), while others are merely nuclear folds. We define the NR as tubular invaginations consisting of either both the inner and outer nuclear membrane, or only the inner nuclear membrane. Specifically, invaginations of both the inner and outer nuclear membrane are also called type II NR, while those of only the inner nuclear membrane are defined as type I NR. The formation and structure of the NR is determined by proteins associated to the nuclear membrane, which induce a high membrane curvature leading to tubular invaginations. Here we review and discuss the current knowledge of nuclear invaginations and the NR in particular. An increase in tubular invaginations of the nuclear envelope is associated with several pathologies, such as laminopathies, cancer, (reversible) heart failure, and Alzheimer’s disease. Furthermore, viruses can induce both type I and II NR. In laminopathies, the amount of A-type lamins throughout the nucleus is generally decreased or the organization of lamins or lamin-associated proteins is disturbed. Also, lamin overexpression or modulation of lamin farnesylation status impacts NR formation, confirming the importance of lamin processing in NR formation. Virus infections reorganize the nuclear lamina via (de)phosphorylation of lamins, leading to an uneven thickness of the nuclear lamina and in turn lobulation of the nuclear membrane and the formation of invaginations of the inner nuclear membrane. Since most studies on the NR have been performed with cell cultures, we present additional proof for the existence of these structures in vivo, focusing on a variety of differentiated cardiovascular and hematopoietic cells. Furthermore, we substantiate the knowledge of the lamin composition of the NR by super-resolution images of the lamin A/C and B1 organization. Finally, we further highlight the essential role of lamins in NR formation by demonstrating that (over)expression of lamins can induce aberrant NR structures.

Replication of cytomegalovirus in human epitheloid diploid cell line

Human diploid BAMB cells with epitheloid morphology, which had been derived from amniotic fluid cells, were capable of supporting the replication of human cytomegalovirus (CMV), without prior treatment of the cells with halogenated pyrimidines. The growth of this virus in BAMB cells and in human diploid fibroblastoid (LEP) cells was compared in parallel tests. Virus replication was slower and less efficient in the former than in the latter system. The most characteristic morphological feature of the CMV-infected BAMB cells was the formation of multinucleated giant cells which frequently contained more than a hundred nuclei; such cells were not seen in LEP cultures. The development of ultrastructural changes was slower in BAMB cells than in LEP cells. The additional most marked differences concerned the place of viral envelopment and the production of cytoplasmic dense bodies. While in LEP cells most nucleocapsids were enveloped from the inner leaflet of the nuclear membrane, in the other system a great majority of the particles acquired their envelopes by budding into vacuoles. Cytoplasmic dense bodies were rare in infected LEP cells but very frequent in BAMB cells. Budding of these structures into vacuoles was also observed.

The effect of influenza virus infection on the agglutinability by concanavalin A of polyoma-transformed BHK-21 cells

Polyoma-transformed (Py-transformed) BHK-21 cells are agglutinated more readily by Concanavalin A (Con A) after they are infected with influenza virus; this agglutination was only slightly affected by fixation with glutaraldehyde or colchicine treatment. It is suggest that the mechanism is not dependent on membrane fluidity. The same amounts of 125i-labelled Con A were bound after infection with influenza virus and after glutaraldehyde fixation with or without colchicine treatment: it seems therefore that new receptors for Con A are not expressed between 90 and 600 minutes after these cells are infected with influenza virus.

Electron microscopical study of initial and final stages of fowl plague virus-replication in chick embryo cells

Cellular uptake of fowl plague virus occurs 10-30 minutes after inoculation of chick embryo cells. The penetration of the virions is by pinocytosis (viropexis); fusion with the cellular membrane has not been observed. After pinocytosis the virions become gradually disintegrated. Budding of newly formed virions from the cellular membrane starts 3 hours post inoculation (p.i.) and reaches its maximum 8 hours p.i. At the same time budding takes place into electron microscopically empty and autophagic vacuoles. Eight hours p.i. about 3 per cent of the infected cells show budding of virions from the surface and into cytoplasmic vacuoles. Labelling of the cellular membrane with ruthenium red demonstrated that these cytoplasmic vacuoles are not simple cross-sections of invaginations of the cellular membrane. Cluster-like structures were found at 6 hours p.i. in the nuclei of infected cells; however, the suggestion that the clusters develop from nucleoli could not be confirmed.