Seed dormancy and delayed flowering in monocarpic plants: selective interactions in a stochastic environment

We explore the effects of temporal variation in multiple demographic rates on the joint evolution of delayed reproduction and seed dormancy using integral projection models (IPMs). To do this, we extend the standard IPM to include a discrete state variable representing the number of seeds in the seed bank, density-dependent recruitment, and temporal variation in demography. Parameter estimates for Carlina vulgaris and Carduus nutans are obtained from long-term studies. Carlina is relatively long lived and has a short-lived seed bank, whereas most Carduus plants flower in their first year and the seed bank is long lived. Using the evolutionarily stable strategy (ESS) approach, we predict the observed flowering and germination strategies. There is excellent agreement between the predictions and the field observations. The effects of temporal variation on the joint ESS are partitioned into components arising from nonlinear averaging (systematic changes in the mean resulting from the interaction between variability and nonlinearity) and nonequilibrium dynamics (fluctuations in fitness caused by temporal variation). This shows that temporal variation can have substantial effects on the observed flowering and germination strategies and that covariance between demographic processes is important. We extend the models to include spatial population structure and assess the robustness of the results from the nonspatial models.     

The cutaneous rabbit illusion affects human primary sensory cortex somatotopically

We used functional magnetic resonance imaging (fMRI) to study neural correlates of a robust somatosensory illusion that can dissociate tactile perception from physical stimulation. Repeated rapid stimulation at the wrist, then near the elbow, can create the illusion of touches at intervening locations along the arm, as if a rabbit hopped along it. We examined brain activity in humans using fMRI, with improved spatial resolution, during this version of the classic cutaneous rabbit illusion. As compared with control stimulation at the same skin sites (but in a different order that did not induce the illusion), illusory sequences activated contralateral primary somatosensory cortex, at a somatotopic location corresponding to the filled-in illusory perception on the forearm. Moreover, the amplitude of this somatosensory activation was comparable to that for veridical stimulation including the intervening position on the arm. The illusion additionally activated areas of premotor and prefrontal cortex. These results provide direct evidence that illusory somatosensory percepts can affect primary somatosensory cortex in a manner that corresponds somatotopically to the illusory percept.     

Immunotherapeutic potential of DISC-HSV and OX40L in cancer

Several vectors, viral and bacterial, have been developed over the past few years for means of generating an effective antitumor immune response. We have developed and studied a “model for immunotherapy” using a viral vector disabled infectious single cycle-herpes simplex virus (DISC-HSV), which efficiently transduces various tumor cell lines and offers a useful vehicle for the further development of cell-based vaccines. The immunotherapeutic potential of DISC-HSV encoding granulocyte macrophage colony stimulating factor (GM-CSF) was demonstrated in a number of murine carcinoma models, leading to complete regression of well-established tumors in up to 70% of the mice. Moreover, the therapeutic potential of DISC-HSV-GM-CSF was significantly enhanced when used in combination therapy with either OX40L or dendritic cells (DC), even in a poorly immunogenic tumor model. The ability of this vector to accept large gene inserts, its good safety profile, its ability to undergo only a single round of infection, the inherent viral immunostimulatory properties and its ability to infect various tumor cell lines efficiently, make DISC-HSV an ideal candidate vector for immunotherapy. The DISC- CT-26 tumor model was used to investigate the mechanisms associated with immunotherapy induced tumor rejection. Although CTL induction, was positively correlated with regression, MHC class I down regulation and accumulation of immature Gr1+ myeloid cells were shown to be the main immuno-suppressor mechanisms operating against regression and associated with progressive tumor growth. The CTL response was associated with the immuno-dominant AH-1 peptide of the retroviral glycoprotein gp70. This model of immunotherapy has provided an opportunity to dissect further the immunological events associated with tumor-rejection and escape. Since other antigens may be important in initiating tumor rejection, we have investigated the expression of MTA-1, an antigen that appears to be expressed widely in human and murine tumors. The immunogenicity of MTA-1 was studied and its potential as a tumor rejection antigen is under investigation. This article is a symposium paper from the conference "Progress in Vaccination against Cancer 2004 (PIVAC 4)", held in Freudenstadt-Lauterbad, Black Forest, Germany, on 22–25 September 2004.     

SCN9A mutations in paroxysmal extreme pain disorder: allelic variants underlie distinct channel defects and phenotypes

Paroxysmal extreme pain disorder (PEPD), previously known as familial rectal pain (FRP, or OMIM 167400), is an inherited condition characterized by paroxysms of rectal, ocular, or submandibular pain with flushing. A genome-wide linkage search followed by mutational analysis of the candidate gene SCN9A, which encodes hNa(v)1.7, identified eight missense mutations in 11 families and 2 sporadic cases. Functional analysis in vitro of three of these mutant Na(v)1.7 channels revealed a reduction in fast inactivation, leading to persistent sodium current. Other mutations in SCN9A associated with more negative activation thresholds are known to cause primary erythermalgia (PE). Carbamazepine, a drug that is effective in PEPD, but not PE, showed selective block of persistent current associated with PEPD mutants, but did not affect the negative activation threshold of a PE mutant. PEPD and PE are allelic variants with distinct underlying biophysical mechanisms and represent a separate class of peripheral neuronal sodium channelopathy.     

Combining conventional QTL analysis and whole-exome capture-based bulk-segregant analysis provides new genetic insights into tuber sprout elongation and dormancy release in a diploid potato population

Tuber dormancy and sprouting are commercially important potato traits as long-term tuber storage is necessary to ensure year-round availability. Premature dormancy release and sprout growth in tubers during storage can result in a significant deterioration in product quality. In addition, the main chemical sprout suppressant chlorpropham has been withdrawn in Europe, necessitating alternative approaches for controlling sprouting. Breeding potato cultivars with longer dormancy and slower sprout growth is a desirable goal, although this must be tempered by the needs of the seed potato industry, where dormancy break and sprout vigour are required for rapid emergence. We have performed a detailed genetic analysis of tuber sprout growth using a diploid potato population derived from two highly heterozygous parents. A dual approach employing conventional QTL analysis allied to a combined bulk-segregant analysis (BSA) using a novel potato whole-exome capture (WEC) platform was evaluated. Tubers were assessed for sprout growth in storage at six time-points over two consecutive growing seasons. Genetic analysis revealed the presence of main QTL on five chromosomes, several of which were consistent across two growing seasons. In addition, phenotypic bulks displaying extreme sprout growth phenotypes were subjected to WEC sequencing for performing BSA. The combined BSA and WEC approach corroborated QTL locations and served to narrow the associated genomic regions, while also identifying new QTL for further investigation. Overall, our findings reveal a very complex genetic architecture for tuber sprouting and sprout growth, which has implications both for potato and other root, bulb and tuber crops where long-term storage is essential.Subject terms: Genetic markers, Next-generation sequencing, Plant breeding, Agricultural genetics, Genetic mapping     

Evaluation of the Litron In Vitro MicroFlow Kit for the flow cytometric enumeration of micronuclei (MN) in mammalian cells

We have evaluated the performance of the prototype In Vitro MicroFlow Kit (Litron Laboratories), which offers a flow cytometric method for scoring micronuclei (MN). This method uses sequential staining to differentiate MN from chromatin fragments derived from apoptotic or necrotic cells. Data were generated using the genotoxins methylmethane sulphonate (MMS), dimethylbenzanthracene (DMBA) and vinblastine, and the non-genotoxins dexamethasone and staurosporine, which are known to induce apoptosis in vitro. The results obtained with these agents were compared with conventional microscopy. For short-duration exposures (3-4h) both manual and flow methodologies demonstrated good concordance, with concentration-related increases in the percentage of MN for MMS, DMBA and vinblastine. Statistically significant increases were observed at > or = 20 and 40 microg/mL, for manual and flow analysis, respectively, for MMS; at 0.5 and 0.75 microg/mL for DMBA; and at 0.035 and 0.04 microg/mL, respectively, for vinblastine. Dexamethasone showed clear negative responses by manual and flow cytometric analysis, with comparable results for both methodologies (all <1.7-fold compared with concurrent vehicle controls). Data for staurosporine, however, were less consistent showing significantly higher flow cytometric MN frequencies compared with those seen after manual analysis. Continuous (24 h) treatments were also conducted with MMS, vinblastine, dexamethasone and staurosporine. There was good concordance between the methodologies for MMS, staurosporine and vinblastine. However, dexamethasone generated discordant results, i.e. microscopic analysis was clearly negative at all doses tested, whereas flow cytometry produced significant increases in MN frequency (up to 8.1-fold at 100 microg/mL compared with the concurrent vehicle control). The inconsistencies observed between flow cytometry and standard microscopy, and the differences in assay sensitivity, particularly for apoptosis-inducing compounds, suggest that the prototype In Vitro MicroFlow Kit requires further refinement. Studies to investigate new parameters to address these issues are now under way and will be reported separately.     

New threshold and confidence estimates for terminal restriction fragment length polymorphism analysis of complex bacterial communities

Terminal restriction fragment length polymorphism (T-RFLP) analysis has the potential to be useful for comparisons of complex bacterial communities, especially to detect changes in community structure in response to different variables. To do this successfully, systematic variations have to be detected above method-associated noise, by standardizing data sets and assigning confidence estimates to relationships detected. We investigated the use of different standardizing methods in T-RFLP analysis of PCR-amplified 16S rRNA genes to elucidate the similarities between the bacterial communities in 17 soil and sediment samples. We developed a robust method for standardizing data sets that appeared to allow detection of similarities between complex bacterial communities. We term this the variable percentage threshold method. We found that making conclusions about the similarities of complex bacterial communities from T-RFLP profiles generated by a single restriction enzyme (RE) may lead to erroneous conclusions. Instead, the use of multiple REs, each individually, to generate multiple data sets allowed us to determine a confidence estimate for groupings of apparently similar communities and at the same time minimized the effects of RE selection. In conjunction with the variable percentage threshold method, this allowed us to make confident conclusions about the similarities of the complex bacterial communities in the 17 different samples.     

The future direction of cholesterol-lowering therapy

PURPOSE OF REVIEW: Observational studies suggest a continuous positive relationship between vascular risk and cholesterol without any lower threshold level. We review recent and future clinical trials addressing the question of optimal treatment goals for cholesterol reduction and how these relate to present guidelines. With increasing focus on greater cholesterol reduction, new approaches to lipid-lowering therapy are being developed; we discuss some of these agents including the new statin, rosuvastatin and novel cholesterol transport inhibitors such as ezetimibe. RECENT FINDINGS: The Heart Protection Study demonstrated that LDL cholesterol reduction to levels as low as 1.7 mmol/l was associated with significant clinical benefit in a wide range of high-risk individuals, irrespective of baseline cholesterol levels, with no apparent threshold level for LDL cholesterol with respect to cardiovascular risk. The Heart Protection Study also demonstrated that the benefits of LDL cholesterol reduction extend into peripheral vascular disease and cerebrovascular disease prevention and suggest that the most recent National Cholesterol Education Program Adult Treatment Panel III guidelines, with LDL cholesterol targets of 2.6 mmol/l, may result in undertreatment of a large number of patients. Various large end-point trials, including Treating to New Targets and Study of Effectiveness of Additional Reductions in Cholesterol and Homocysteine will attempt to further address the issue of optimal LDL cholesterol reduction. New therapies are being developed to meet the challenge of more intensive cholesterol lowering. Rosuvastatin is a potent, hydrophilic enantiomeric statin producing reductions in LDL cholesterol of 40-69% over its dose range of 5-80 mg. Ezetimibe is a selective cholesterol absorption inhibitor, with a site of action at the intestinal epithelium. Optimum reductions in LDL cholesterol of up to 25 and 60% reduction in chylomicron cholesterol content are seen with a 10-mg dose. SUMMARY: Evidence is accumulating supporting the safety and benefits of aggressive cholesterol reduction, with no apparent threshold for LDL cholesterol. New therapies will aid in achieving lower cholesterol levels and the use of combination therapies targeting different aspects of cholesterol metabolism may produce additional benefits. Outcome studies are awaited to further address these issues.