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Transmission Electron Microscopy: A Surgical Pathology Tool for Neuroblastoma

Pediatric small round blue cell tumors (PSRBCT) are an intriguing and challenging collection of neoplasms. Light microscopy of small round blue cell ...

University of Ottawa

The expression of nonagglutinating fimbriae (NAF) and mannose-resistant/Proteus-like (MR/P) pili in swarming colonies of Proteus mirabilis was investigated. Elongated swarmer cells do not express pili, and the relative number of bacteria expressing NAF during swarming and early consolidation phases was very low (<5%). Relative expression of NAF in a terrace increased to approximately 30% at 48 h. We also determined the expression of NAF and MR/P pili in two phenotypically distinguishable regions of each terrace. The expression of both NAF and MR/P pili was always higher in the region closer (proximal) to the middle of the colony than in the distal region of the terrace. The relative numbers of bacteria expressing NAF or MR/P pili in the proximal region were between 39.1 and 63% and between 5.9 and 7.7%, respectively. In the distal region, expression levels were between 20.8 and 27.3% and between 3.7 and 5. 6%, respectively. A time course experiment testing NAF expression in both the proximal and distal regions of a terrace indicated that NAF expression in the proximal regions was always higher than in the distal regions and increased to a plateau 40 to 50 h after the start of the swarming phase for any given terrace. These results indicate that expression of NAF or MR/P pili in swarming colonies of P. mirabilis is highly organized, spatially and temporally. The significance of this controlled differentiation remains to be uncovered.

Differential expression of nonagglutinating fimbriae and MR/P pili in swarming colonies of Proteus mirabilis.

Uncoating of influenza occurs in endosomes where the acid environment is instrumental in membrane fusion and the dissociation of the ribonucleoprotein (RNP) from matrix protein by the action of the hemagglutinin and M2 protein ion channels, respectively. Earlier studies have shown that low pH treatment results in the release of M1 protein from RNP. To obtain RNP free of M1 protein, we attempted to isolate RNP by velocity sedimentation on pH 5 glycerol gradients; however, the RNP sedimented as pellets under centrifugation conditions that had previously resolved RNP on neutral gradients. The increase in sedimentation rate occurred between pH 5.6 and 6.0 and was reversible for a portion of the RNP on raising the pH to neutrality. RNP isolated from infected cells or virions sedimented on acidification and was seen to form clumps visible by electron microscopy. If acidification preceded NP40 detergent lysis, virion RNP appeared to be released as genomic complexes. The pH threshold for viral membrane fusion was 5.8 indicating that the same pH condition also resulted in aggregation of RNP. Because exposure of virions to pH 5 occurs during uncoating in endosomes and is essential for infectivity, it is possible that low pH-induced RNP aggregation may facilitate aspects of viral uncoating such as dissociation of RNP from M1 or transport of genomes to the nucleus.

Article	Year
Differential expression of nonagglutinating fimbriae and MR/P pili in swarming colonies of Proteus mirabilis. Journal of bacteriology\| PubMed ID: 10322025	1999
Aggregation of influenza virus ribonucleocapsids at low pH. Virus research\| PubMed ID: 12034481	2002

Rod Nicholls

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