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J Perreault

Publications and source records attributed to J Perreault.

13 recordsLinked to original sources
PubMed1999

Subcellular localization and rolling circle replication of peach latent mosaic viroid: hallmarks of group A viroids.

We characterized the peach latent mosaic viroid (PLMVd) replication intermediates that accumulate in infected peach leaves and determined the tissue and subcellular localization of the RNA species. Using in situ hybridization, we showed that PLMVd strands of both plus and minus polarities concentrate in the cells forming the palisade parenchyma. At the cellular level, PLMVd was found to accumulate predominantly in chloroplasts. Northern blot analyses demonstrated that PLMVd replicates via a symmetric mode involving the accumulation of both circular and linear monomeric strands of both polarities. No multimeric conformer was detected, indicating that both strands self-cleave efficiently via their hammerhead sequences. Dot blot hybridizations revealed that PLMVd strands of both polarities accumulate equally but that the relative concentrations vary by more than 50-fold between peach cultivars. Taken together these results establish two hallmarks for the classification of viroids. Group A viroids (e.g., PLMVd), which possess hammerhead structures, replicate in the chloroplasts via the symmetric mode. By contrast, group B viroids, which share a conserved central region, replicate in the nucleus via an asymmetric mechanism. This is an important difference between self-cleaving and non-self-cleaving viroids, and the implications for the evolutionary origin and replication are discussed.

Fruit↗
PubMed1996

Postbinding events mediated by human immunodeficiency virus type 1 are sensitive to modifications in the D4-transmembrane linker region of CD4.

Evidence from both structural and functional studies of the CD4 molecule suggests that several domains, including the transmembrane (TM) domain and the adjoining extracellular region (D4-TM linker), contribute to the post-gp12O-binding events leading to human immunodeficiency virus-mediated membrane fusion. To investigate such a role in syncytium formation and cell-free infectivity, we generated several deletion and substitution mutations in the TM and D4-TM linker regions of the CD4 molecule. We found that while the TM domain of CD4 was dispensable for cell-cell and virus-cell interactions, modifications in the D4-TM linker led to perturbations in both processes. Deletion of the five amino acid residues linking D4 to the TM domain resulted in a delayed and reduced capacity to form syncytia, whereas replacement of the residues with the heterologous sequence from the CD8 molecule restored the kinetic profile to wild-type CD4 levels. On the other hand, both mutants of the CD4 D4-TM linker demonstrated delayed cell-free human immunodeficiency virus type 1 infectivity profiles. The defective fusion capacity may be linked to structural perturbations identified with anti-CD4 monoclonal antibodies in the D1-D2 interface and D3 domain of the deletion mutant yet absent in D1 and D4. While all cells were found to bind comparable levels of gp120, both D4-TM linker mutants appeared to induce a decrease in the V3 loop exposure of bound gp120. This underexposure may explain the delays in cell-free infectivities observed for both of these mutants. Together, these findings confirm a role for regions of the CD4 molecule located outside D1 in post-gp120-binding events and suggest that the D4-TM interface contributes to the conformational changes that direct the fusion process.

Binding Sites↗
PubMed1995

A rapid PCR-based test for the endogenous viral element ev3 of chickens.

A short fragment of chicken genomic DNA encompassing the insertion site of the endogenous avian leucosis viral element ev3 was isolated using the inverse polymerase chain reaction (inverse PCR) technique. The nucleotide sequence of the unoccupied site was used to design PCR primers that can be used to unambiguously determine the genetic status of any chicken, with respect to ev3. Screening of a small number of individuals from exotic breeds of chickens suggested that the frequency of ev3 is highly variable. The ev3 integration site shows a high degree of sequence homology with the macrophage-specific tyrosine kinase gene, bmk, in mice.

Animals↗
PubMed1993

Rapid apoptotic cell death of B-cell hybridomas in absence of gene expression.

Apoptosis is an active form of cell death which plays an important role in different biological processes. The induction of apoptosis usually requires de novo gene expression but has also been observed in certain types of cells in absence of gene expression or following a block of gene expression. We show here that inhibition of macromolecular synthesis induced the rapid apoptotic death of most antibody-secreting B-cell hybridomas. The effect was observed in presence of both protein synthesis (cycloheximide [CHX]) and transcription (actinomycin D [Act D]) inhibitors and was characterized by extensive degradation of nucleic acids (DNA and RNA) within 2-3 h of treatment. The CHX treatment not only severely impaired the proliferation of the cells but also resulted in the loss of cell viability (MTT assay) without the need of de novo gene expression. The susceptibility to apoptosis varied among different B-cell hybridomas and was inherited from the SP2/0 myeloma cell fusion partner. These results indicate the constitutive activation of a death program in B-cell hybridomas and its inhibition at a late stage by the continuous expression of gene(s) coding for short-lived protein(s). The occurrence of this phenomenon may well be related to the abundant and deregulated (translocation) expression, in this type of cells, of the c-myc gene which has recently been shown to be a potent inducer of apoptosis in growth-arrested fibroblasts.

Animals↗
PubMed1993

Essential role of optimal protein synthesis in preventing the apoptotic death of cultured B cell hybridomas.

The monoclonal antibody productivity of cell culture systems is strongly dependent on the maintenance of hybridoma cell viability. We report that partial (< 50%) and transient (3 h) inhibition of protein synthesis by cycloheximide or deprivation of an essential amino acid induces apoptosis (programmed cell death) in B cell hybridomas. This unusual mechanism of apoptosis induction is likely to play a significant role in limiting cell viability in batch and perfusion cultures of hybridomas and emphasizes the importance of constantly maintaining a near optimal rate of macromolecular synthesis by optimization of all culture parameters. Inhibition of apoptosis in hybridomas by cell engineering and other technologies should permit, in the near future, a significant increase in the antibody productivity of existing cell culture systems.

Animals↗
PubMed1986

[Quebec's population decline: if it is foreseeable, is it avoidable?].

"Quebec's fertility is the lowest in Canada, and it is most likely that its population is heading for a decline. In this paper, the authors try to make explicit some of the scenarios which could prevent this decline. They first briefly present the current trends and specify the assumptions used in the simulation. Then, they analyse the results by investigating the onset of the decline and the maximum size of the population. And finally, they present some of the replacement scenarios which may prevent the decline." (SUMMARY IN ENG AND SPA)

Americas↗
PubMed1984

[A half-million Indians registered in Canada in the year 2000?].

"The Indian population of Canada has grown from 277,000 in 1973 to about 335,000 in 1982.... During the next 20 years the Indian population will grow at a greater rate than the Canadian population, and at the turn of the century it may well reach 450,000 persons. On the one hand, [the authors] present the demographic situation of Canada's Registered Indians, from 1967 to 1981 [and] examine the components of growth of this sub-population. On the other hand, [they] analyse the foreseen evolution of the Registered Indian population, till the year 2000, its size, demographic structure, as well as its distribution by type of habitat." The focus is on the province of Quebec. (summary in ENG, SPA)

Americas↗