Although non-obese diabetic (NOD) mice spontaneously develop T cell autoimmunity, it is not clear whether this phenomenon results from a defect in tolerance to self-Ag. Furthermore, as autoimmunity ...has been postulated to result from T cell responses directed toward self-peptides that bind with low affinity to NOD I-A(g7) MHC class II molecules, it is important to determine whether the expression of such peptides induces tolerance. We have constructed NOD transgenic (Tg) mice expressing the Leishmania antigen receptor for C kinase (LACK) Ag in either the thymus or pancreatic beta cells. We identified LACK peptides that were the targets of T cells in LACK-immunized NOD mice while binding to I-A(g7) with low affinity. While CD4(+) T cells from NOD mice secreted IFN-gamma, IL-4, IL-5 and IL-10 in response to LACK, those from LACK-expressing Tg mice secreted reduced levels of cytokines. Experiments using peptide/MHC multimers showed that LACK-expressing Tg mice exhibited self-reactive CD4(+) T cells with impaired proliferation capabilities. Hence, even self-peptides that bind to I-A(g7) with low affinity can induce tolerance in NOD mice. This result is important in light of the commonly held hypothesis that T cells reacting to peptides that bind to MHC with low affinity escape tolerance induction and cause autoimmunity.
Resistance and susceptibility to Leishmania major in mice are determined by multiple genes and correlate with the preferential development of Th1 and Th2 responses, respectively. Here, we found that ...CD11b super(+) dendritic cells (DCs) prime parasite-specific CD4 super(+) T cells in both susceptible BALB/c (H2-d) and resistant B10.D2 (H2-d) mice. However, BALB/c and B10.D2 DCs from L. major-infected mice differ in their ability to polarize naive T cells into Th1 or Th2 effector cells. This difference is cell-intrinsic, is not restricted to H2-d mice, and is observed with both parasite-specific and allospecific CD4 super(+) T cells. Thus, strain-specific differences within CD11b super(+) DCs influence the ability of inbred mice to mount polarized CD4 super(+) T cell responses.
Mycorrhizas Peterson, R. Larry; Massicotte, Hugues B; Melville, Lewis H
Mycorrhizas,
c2004, 2003, 2004-01-01
eBook
A summary of all the mycorrhizal types from a morphological and anatomical perspective is presented in this beautifully illustrated book. Specialized topics are highlighted in each chapter for those ...who wish to pursue mycorrhizal associations in more depth.
Logging in the boreal forest may benefit moose by increasing food availability. However, the influence of tree plantations on moose behavior, especially on moose spatial ecology, is poorly ...understood. We assessed the impacts of black spruce plantations on moose winter distribution at a landscape scale in the Bas-Saint-Laurent region (Québec, Canada). We used winter aerial surveys to examine relationships among plantation characteristics and other habitat variables known to affect moose distribution. The total area of plantations positively influenced moose abundance, but highly aggregated plantations resulted in fewer moose. Moose abundance was also positively associated with food availability and the density of edges between stands providing cover and stands offering high food availability, but moose abundance was negatively associated with road density. Although plantation characteristics were less influential than habitat variables related to foraging and predator avoidance, we demonstrate that the area of black spruce plantations and their configuration should be considered in moose management. We conclude that an integrated management strategy is needed to find a balance between overdeveloped road networks (needed to join homogeneously distributed plantations) and agglomerated plantations in order to mitigate impacts on moose winter distribution.
Habitat loss and fragmentation are recognized as major threats to biodiversity. Their respective effects, however, are sometimes not well distinguished, even though habitat loss is recognized as the ...most important source of variation affecting species abundance and richness at the landscape scale. As ‘
habitat’ is a species-specific concept (based on species perception of its environment), habitat loss and fragmentation studies should be conducted on a species-specific basis. We here assessed the influence of habitat loss and fragmentation in the context of a boreal forest considering forest clearcutting as an anthropogenic disturbance inducing mature forest loss and fragmentation that has a potential impact on wildlife. Using 16 simulated patterns of mature forest loss and fragmentation and three natural landscapes as replicates, we assessed the respective influence of forest loss and fragmentation on the abundance of 10 bird species common in the boreal forest of eastern Canada. Species–habitat relationships were modeled through habitat use models that were utilized to predict abundance of the 10 species within each combination of loss and fragmentation patterns (3 landscapes
×
16 patterns). We used three-way ANOVAs to assess the effects of mature forest loss, fragmentation and replicates (random effect) on species abundance. Our results indicated that: (1) variation in species abundance mostly depended on mature forest loss, followed by static landscape attributes other than cutovers (e.g. streams, lakes, roads) and finally by fragmentation and (2) responses to mature forest loss and fragmentation differed among species, not necessary in relation to the successional status but in relation to their perception of their environment. Decreasing detrimental effects of mature forest loss through conservation of large continuous patches of forest may be suitable to maintain abundances of mature forest bird species. Our results highlight that studies aiming to quantify effects of habitat loss and fragmentation on wildlife should be conducted on a species-specific basis and use several landscape replicates to avoid potentially biased results.
Background Albeit the molecular mechanisms of gene expression are well documented, our understanding of their dynamics is much less advanced. Recent experimental evidence has revealed that gene ...expression might be accurately organized in space, with several molecular actors localized to specific positions in the cell. However, the influence of this spatial localization on the dynamics of gene expression is unclear. This issue is also central in synthetic biology, where one usually considers the spatial localization in the cell of the genes of the inserted synthetic construct as irrelevant for its temporal dynamics. Results Here, we assessed the influence of the spatial distribution of the genes on the dynamics of 3-gene transcriptional ring networks regulated by repression, i.e. repressilator circuits, using individual-based modelling to simulate their dynamics in two and three space dimensions. Our simulations suggest that variations of spatial parameters -- namely the degree of demixing of the positions of the gene or the spatial range of the mRNA and proteins (i.e. the typical distance they travel before degradation) -- have dramatic effects by switching the dynamical regime from spontaneous oscillations to a stationary state where each species fluctuates around a constant value. By analogy with the bifurcations arising from the variation of kinetic parameters, we referred to those transitions as space-induced bifurcations. Conclusions Taken together, our results strongly support the idea that the spatial organization of the molecular actors of transcriptional networks is crucial for the dynamics of gene expression and suggest that the spatial localization of the synthetic genes in the cell could be used as an additional toggle to control the dynamics of the inserted construct in synthetic biology experiments.
PDF
