Positive interactions between herbivores and plant diversity shape forest regeneration

The effects of herbivores and diversity on plant communities have been studied separately but rarely in combination. We conducted two concurrent experiments over 3 years to examine how tree seedling diversity, density and herbivory affected forest regeneration. One experiment factorially manipulated plant diversity (one versus 15 species) and the presence/absence of deer (Odocoileus virginianus). We found that mixtures outperformed monocultures only in the presence of deer. Selective browsing on competitive dominants and associational protection from less palatable species appear responsible for this herbivore-driven diversity effect. The other experiment manipulated monospecific plant density and found little evidence for negative density dependence. Combined, these experiments suggest that the higher performance in mixture was owing to the acquisition of positive interspecific interactions rather than the loss of negative intraspecific interactions. Overall, we emphasize that realistic predictions about the consequences of changing biodiversity will require a deeper understanding of the interaction between plant diversity and higher trophic levels. If we had manipulated only plant diversity, we would have missed an important positive interaction across trophic levels: diverse seedling communities better resist herbivores, and herbivores help to maintain seedling diversity.     

Proteomic analysis identifies in vivo candidate matrix metalloproteinase‐9 substrates in the left ventricle post‐myocardial infarction

Matrix metalloproteinase‐9 (MMP‐9) deletion has been shown to improve remodeling of the left ventricle post‐myocardial infarction (MI), but the mechanisms to explain this improvement have not been fully elucidated. MMP‐9 has a broad range of in vitro substrates, but relevant in vivo substrates are incompletely defined. Accordingly, we evaluated the infarct regions of wild‐type (wt) and MMP‐9 null (null) mice using a proteomic strategy. Wt and null groups showed similar infarct sizes (48±3 in wt and 45±3% in null), indicating that both groups received an equal injury stimulus. Left ventricle infarct tissue was homogenized and analyzed by 2‐DE and MS. Of 31 spot intensity differences, the intensities of 9 spots were higher and 22 spots were lower in null mice compared to wt (all p<0.05). Several extracellular matrix proteins were identified in these spots by MS, including fibronectin, tenascin‐C, thrombospondin‐1, and laminin. Fibronectin was observed on the gels at a lower than expected molecular weight in the wt group, which suggested substrate cleavage, and the lower molecular weight spot was observed at lower intensity in the MMP‐9 null group, which suggested cleavage by MMP‐9. Immunoblotting confirmed the presence of fibronectin cleavage products in the wt samples and lower levels in the absence of MMP‐9. In conclusion, examining infarct tissue from wt and MMP‐9 null mice by proteomic analysis provides a powerful and unique method to identify in vivo candidate MMP substrates.     

Ligand-Induced Translocation of Epidermal Growth Factor Receptor to the Nucleus of NR6/HER Fibroblasts Is Serum Dependent

Ligand-induced translocation of epidermal growth factor receptors (EGF-R) to the nucleus of NR6/HER fibroblasts has been studied by immunoelectron microscopy. Following treatment of NR6/HER cells with epidermal growth factor (EGF) for 1 h, there was a decrease in EGF-R labeling at the plasma membrane and a corresponding increase in EGF-R in the nucleus. This was preceded by a rapid and sustained increase in nuclear phosphotyrosine content, detectable within 2 min of EGF treatment. EGF-R translocation into the nucleus was completely prevented by 18 h serum starvation prior to treatment with EGF. These results indicate that translocation of EGF-R to the nucleus is a controlled process and they suggest theft EGF-R may directly influence nuclear function.     

Multiplexed expression and screening for recombinant protein production in mammalian cells

Background  

A variety of approaches to understanding protein structure and function require production of recombinant protein. Mammalian based expression systems have advantages over bacterial systems for certain classes of protein but can be slower and more laborious. Thus the availability of a simple system for production and rapid screening of constructs or conditions for mammalian expression would be of great benefit. To this end we have coupled an efficient recombinant protein production system based on transient transfection in HEK-293 EBNA1 (HEK-293E) suspension cells with a dot blot method allowing pre-screening of proteins expressed in cells in a high throughput manner.     

Aging alters the functional expression of enzymatic and non-enzymatic anti-oxidant defense systems in testicular rat Leydig cells

In aged rats, trophic hormone-stimulated testosterone secretion by isolated Leydig cells is greatly reduced. The current studies were initiated to establish a functional link between excess oxidative stress and the age-related decline in steroidogenesis. Highly purified Leydig cell preparations obtained from 5-month (young mature) and 24-month (old) Sprague-Dawley rats were employed to measure and compare levels of lipid peroxidation, non-enzymatic (alpha-tocopherol, ascorbic acid, and reduced/oxidized glutathione) and enzymatic (Cu, Zn-superoxide dismutase, Cu, Zn-SOD; Mn-superoxide dismutase, Mn-SOD; glutathione peroxidase-1, GPX-1, and catalase, CAT) anti-oxidants. The extent of lipid peroxidation (oxidative damage) in isolated membrane fractions was quantified by measuring the content of thiobarbituric acid-reactive substances (TBARS) under basal conditions, or in the presence of non-enzymatic or enzymatic pro-oxidants. Membrane preparations isolated from Leydig cells from old rats exhibited two- to three-fold enhancement of basal TBARS formation. However, aging had no significant effect on TBARS formation in response to either non-enzymatic or enzymatic pro-oxidants. Among the non-enzymatic anti-oxidants, the levels of reduced glutathione were drastically reduced during aging, while levels of alpha-tocopherol and ascorbic acid remained unchanged. Both steady-state mRNA levels and catalytic activities of Cu, Zn-SOD, Mn-SOD, and GPX-1 were also significantly lower in Leydig cells from 24-month-old rats as compared with 5-month-old control rats. In contrast, neither mRNA levels nor enzyme activity of catalase was sensitive to aging. From these data we conclude that aging is accompanied by reduced expression of key enzymatic and non-enzymatic anti-oxidants in Leydig cells leading to excessive oxidative stress and enhanced oxidative damage (lipid peroxidation). It is postulated that such excessive oxidative insult may contribute to the observed age-related decline in testosterone secretion by testicular Leydig cells.     

An aetiological study of 290 XXY males,with special reference to the role of paternal age

Summary Data on 290 non-mosaic 47,XXY males have been analysed for possible associations with parental ages at birth, season of birth, sex ratio among sibs, and twinning. Comparison with matched population controls revealed a highly significant association with parental age, which was fully explained by dependence on maternal age and maternal age alone. The maternal age effect was determined with greater precision than in an earlier study of the same material, in which siblings were used as controls, and was estimated to result in an increased risk of between 5% and 10% per annum (p.a.). The estimated independent effect of paternal age, after fitting maternal age, was marginally (but not significantly) negative, and excluded an increased risk in excess of 3% p.a. Paternal age therefore appears to have little if any independent significance in the aetiology of 47,XXY. After correcting for seasonal variations in the population birth rate and smoothing, there was a peak of XXY births in March and a trough in November. Though not statistically significant, the pattern resembled that reported in previous studies, and was similar for both younger and older mothers. The twinning rate for both the XXYs and their sibs, and the sex ratio among the latter, were close to the corresponding population values.     

Optimal dispatching of multipriority jobs to two heterogeneous workstations

The general problem scenario of this paper is the following: Jobs of various priorities, stationed in a common storage area, are waiting to be dispatched to two non-identical workstations. Any of the waiting jobs can be accessed from the storage at any given time. Each job can be processed on either of the workstations, but once a job has been assigned it may not be preempted. By job priority it is meant that a higher priority job has disptach preference over a lower priority job. The processing time of a job on a given workstation is assumed to be random, the distribution being dependent on the job type and the configuration of the workstation. Specifically, the first problem studied considers only two classes of jobs: (1) “hot” jobs, whose processing is to be expedited and thus have the higher dispatch priority, and (2) “routine” jobs which may be assigned to an available workstation only if the workstation has been rejected by all “hot” jobs. The processing times are assumed to be exponentially distributed with means depending on the job class and workstation. We assume that, on the average, one workstation is faster than the other with regard to processing any job. The dispatching objective for each job class is to minimize its expected flowtime. It is shown that threshold dispatching policies are optimal for this problem. That is, the faster processor should be utilized whenever possible, and for each class there exists an explicit threshold such that when the number of jobs of that class in the buffer exceeds this threshold then a job of that class is dispatched to the slower processor, otherwise these jobs wait for the faster processor to become available. For the higher priority jobs, this threshold is shown to be a function only of the various processing rates of the two workstations. For the lower priority jobs, the threshold also depends on the number of higher priority jobs in the buffer. The results is extended to a system with n priority classes. Again, it is shown that when the processing times are exponentially distributed with different rates and the dispatching objective for each class is to minimize its expected flowtime, the optimal dispatching policies are of threshold type. Explicit thresholds are easily derived.