Facilitation in an unproductive boreal forest understorey community

Questions: We tested the hypothesis that if competition had a significant influence in structuring this boreal plant community, removal of neighbours, addition of fertilizer and addition of water would all benefit the transplanted seedlings. Alternatively, if facilitation had a greater influence, then removal of neighbours would be detrimental to the transplants but fertilization and watering would still be beneficial. Location: Understorey of the boreal forest in southwestern Yukon Territory, Canada (138°22′W; 61°02′N). Methods: Ten of the most common species were transplanted as seedlings into transects from which all neighbours had been removed, and also into transects with intact vegetation. We used a factorial design with two levels of watering and two levels of fertilization; this allowed us to test effects at both species and community level. Results: The summed survival and total biomass of all transplants was significantly higher in the presence of neighbours than without neighbours, indicating a facilitative effect of neighbouring plants, but there were significant increases in only six of the ten species. The combined survival and biomass of all species increased with watering, survival decreased and biomass increased with fertilization, but only two species had significant responses to fertilization: Anenome parviflora decreased and Mertensia paniculata increased in biomass. Watering increased the biomass of Achillea millefolium, Festuca altaica and Solidago multiradiata; there were also some interaction effects. Conclusions: (1) The presence of neighbours was generally facilitative. (2) Fertilization had negligible effects, and watering had minor beneficial effects. (3) This study demonstrates the importance of facilitation in structuring this boreal understorey community.     

Combination of dipeptidylpeptidase IV inhibitor and low dose thiazolidinedione: preclinical efficacy and safety in db/db mice

Thiazolidinediones (TZDs) are currently the most efficacious class of oral antidiabetics. However, they carry the burden of weight gain and haemodilution, which may lead to cardiovascular complications. The present study was designed to ascertain whether a combination of dipeptidyl peptidase IV (DPP IV) inhibitor with low dose of a thiazolidinedione absolves TZD associated weight gain and oedema without compromising its efficacy. In this study, we examined the efficacy and safety of lower dose (1 mg/kg/day) of rosiglitazone, a thiazolidinedione, in combination with 5 mg/kg/day dose of LAF-237 (vildagliptin), a known DPP IV inhibitor, in aged db/db mice after 14 days of treatment and compared the combination with therapeutic dose (10 mg/kg) of rosiglitazone. The combination therapy showed similar efficacy as that of 10 mg/kg/day rosiglitazone in lowering random blood glucose (53.8%, p<0.001 and 54.3%, p<0.001 respectively), AUC ((0-120) min) during oral glucose tolerance test (OGTT) (38.6 %, p<0.01; 38.3%, p<0.01 respectively) and triglyceride levels (63.9% and 61% respectively; p<0.01). Plasma active glucagon like peptide-1 (GLP-1) and insulin levels were found to be elevated significantly (p<0.01 and p<0.05 respectively) in both LAF-237 and combination treated groups following oral glucose load. LAF-237 alone had no effect on random glucose and glucose excursion during OGTT in severely diabetic db/db mice. Interestingly, the combination treatment showed no significant increase in body weight as compared to the robust weight gain by therapeutic dose of rosiglitazone. Rosiglitazone at 10 mg/kg/day showed significant reduction (p<0.05) in haematocrit, RBC count, haemoglobin pointing towards haemodilution associated with increased mRNA expression of Na(+), K(+)-ATPase-alpha and epithelial sodium channel gamma (ENaCgamma) in kidney. The combination therapy escaped these adverse effects. The results suggest that combination of DPP IV inhibitor with low dose of thiazolidinedione can interact synergistically to represent a therapeutic advantage for the clinical treatment of type 2 diabetes without the adverse effects of haemodilution and weight gain associated with thiazolidinediones.     

Lamin A/C binding protein LAP2alpha is required for nuclear anchorage of retinoblastoma protein

The phosphorylation-dependent anchorage of retinoblastoma protein Rb in the nucleus is essential for its function. We show that its pocket C domain is both necessary and sufficient for nuclear anchorage by transiently expressing green fluorescent protein (GFP) chimeras of Rb fragments in tissue culture cells and by extracting the cells with hypotonic solutions. Solid phase binding assays using glutathione S-transferase-fusion of Rb pockets A, B, and C revealed a direct association of lamin C exclusively to pocket C. Lamina-associated polypeptide (LAP) 2alpha, a binding partner of lamins A/C, bound strongly to pocket C and weakly to pocket B. When LAP2alpha was immunoprecipitated from soluble nuclear fractions, lamins A/C and hypophosphorylated Rb were coprecipitated efficiently. Similarly, immunoprecipitation of expressed GFP-Rb fragments by using anti-GFP antibodies coprecipitated LAP2alpha, provided that pocket C was present in the GFP chimeras. On redistribution of endogenous lamin A/C and LAP2alpha into nuclear aggregates by overexpressing dominant negative lamin mutants in tissue culture cells, Rb was also sequestered into these aggregates. In primary skin fibroblasts, LAP2alpha is expressed in a growth-dependent manner. Anchorage of hypophosphorylated Rb in the nucleus was weakened significantly in the absence of LAP2alpha. Together, these data suggest that hypophosphorylated Rb is anchored in the nucleus by the interaction of pocket C with LAP2alpha-lamin A/C complexes.     

Lipophilic methylene blue analogues enhance mitochondrial function and increase frataxin levels in a cellular model of Friedreich’s ataxia

Friedreich’s ataxia (FRDA) is an autosomal recessive neurodegenerative disorder resulting from reduced expression of the protein frataxin (FXN). Although its function is not fully understood, frataxin appears to help assemble iron sulfur clusters; these are critical for the function of many proteins, including those needed for mitochondrial energy production. Finding ways to increase FXN levels has been a major therapeutic strategy for this disease. Previously, we described a novel series of methylene violet analogues and their structural optimization as potential therapeutic agents for neurodegenerative and mitochondrial disorders. Presently, a series of methylene blue analogues has been synthesized and characterized for their in vitro biochemical and biological properties in cultured Friedreich’s ataxia lymphocytes. Favorable methylene blue analogues were shown to increase frataxin levels and mitochondrial biogenesis, and to improve aconitase activity. The analogues were found to be good ROS scavengers, and able to protect cultured FRDA lymphocytes from oxidative stress resulting from inhibition of complex I and from glutathione depletion. The analogues also preserved mitochondrial membrane potential and augmented ATP production. Our results suggest that analogue 5, emerging from the initial structure of the parent compound methylene blue (MB), represents a promising lead structure and lacks the cytotoxicity associated with the parent compound MB.     

Description and mapping of the resistance of DBA/2 mice to TNF-induced lethal shock

In our search for genes that inhibit the inflammatory effects of TNF without diminishing its antitumor capacities we found that, compared with C57BL/6 mice, DBA/2 mice exhibit a dominant resistance to TNF-induced lethality. Tumor-bearing (C57BL/6 x DBA/2)(BXD)F(1) mice completely survived an otherwise lethal TNF/IFN-gamma-antitumor therapy with complete regression of the tumor. This was not the case for C57BL/6 mice. Genetic linkage analysis revealed that TNF resistance is linked to a major locus on distal chromosome 6 and a minor locus on chromosome 17. Compared with littermate controls, chromosome substitution mice carrying a DBA/2 chromosome 6 in a C57BL/6 background were significantly protected against TNF and TNF/IFN-gamma, albeit less so than DBA/2 mice. Definition of a critical region of 13 Mb on chromosome 6 was the highest mapping resolution obtained. Further analysis of candidate genes may provide a powerful tool to control TNF-induced pathologies in humans.     

Cost of resistance and tolerance under competition: the defense-stress benefit hypothesis

Defense costs provide a major explanation for why plants in nature have not evolved to be better defended against pathogens and herbivores; however, evidence for defense costs is often lacking. Plants defend by deploying resistance traits that reduce damage, and tolerance traits that reduce the fitness effects of damage. We first tested the defense-stress cost (DSC) hypothesis that costs of defenses increase and become important under competitive stress. In a greenhouse experiment, uniparental maternal families of the host plant Arabis perennans were grown in the presence and absence of the bunch grass Bouteloua gracilis and the herbivore Plutella xylostella. Costs of resistance and tolerance manifest as reduced growth in the absence of herbivory were significant when A. perennans grew alone, but not in the competitive environment, in contrast to the DSC hypothesis. We then tested the defense-stress benefit (DSB) hypothesis that plant defenses may benefit plants in competitive situations thereby reducing net costs. For example, chemical resistance agents and tolerance may also have functions in competitive interactions. To test the DSB hypothesis, we compared differentially competitive populations for defense costs, assuming that poorer competitors from less dense habitats were less likely to have evolved defenses that also function in competition. Without competitive benefits of defenses, poorer competitors were expected to have higher net costs of defenses under competition in accordance with DSB. Populations of A. perennans and A. drummondii that differed dramatically in competitiveness were compared for costs, and as the DSB hypothesis predicts, only the poor competitor population showed costs of resistance under competition. However, cost of tolerance under competition did not differ among populations, suggesting that the poor competitors might have evolved a general stress tolerance. Although the DSC hypothesis may explain cases where defense costs increase under stress, the DSB hypothesis may explain some cases where costs decrease under competitive stress.     

Dual source and target of heparin-binding EGF-like growth factor during the onset of implantation in the hamster

Heparin binding EGF-like growth factor (HB-EGF), encoded by the Hegfl gene, is considered as an important mediator of embryo-uterine interactions during implantation in mice. However, it is unknown whether HB-EGF is important for implantation in species with different steroid hormonal requirements. In mice and rats, maternal ovarian estrogen and progesterone (P(4)) are essential to implantation. In contrast, blastocyst implantation can occur in hamsters in the presence of P(4) alone. To ascertain whether HB-EGF plays any role in implantation in hamsters, we examined the expression, regulation and signaling of HB-EGF in the hamster embryo and uterus during the periimplantation period. We demonstrate that both the blastocyst and uterus express HB-EGF during implantation. Hegfl is expressed solely in the uterine luminal epithelium surrounding the blastocyst prior to and during the initiation of implantation. Hypophysectomized P(4)-treated pregnant hamsters also showed a similar pattern of implantation-specific Hegfl expression. These results suggest that uterine Hegfl expression at the implantation site is driven by either signals emanating from the blastocyst or maternal P(4), but not by maternal estrogen. However, in ovariectomized hamsters, uterine induction of Hegfl requires the presence of estrogen and activation of its nuclear receptor (ER), but not P(4). This observation suggests an intriguing possibility that an estrogenic or unidentified signal from the blastocyst is the trigger for uterine HB-EGF expression. An auto-induction of Hegfl in the uterus by blastocyst-derived HB-EGF is also a possibility. We further observed that HB-EGF induces autophosphorylation of ErbB1 and ErbB4 in the uterus and blastocyst. Taken together, we propose that HB-EGF production and signaling by the blastocyst and uterus orchestrate the 'two-way' molecular signaling to initiate the process of implantation in hamsters.