DisSIRTing on LXR and cholesterol metabolism

The NAD-dependent deacetylase SIRT1 regulates lipid and carbohydrate metabolism and has been shown to extend life span in several species. In a recent issue of Molecular Cell, Li et al. (2007) demonstrate that SIRT1 deacetylates and activates the nuclear receptor LXR by favoring its ligand-dependent proteasomal degradation, thereby potentially regulating reverse cholesterol transport.     

Group defense by colony-founding queens in the fire ant Solenopsis invicta

Mutualistic associations among nonkin can form when animalsin groups have a greater chance of overcoming challenges presentedby the environment than do solitary animals. Colony foundingby small groups of unrelated queens, a habit documented in severalspecies of ants, is often interpreted as a mutualistic interactionselected by intense competition among incipient colonies. However,many new colonies in these species are founded in areas wheretheir chief enemies are mature ant colonies, rather than othernewly founded colonies. In this study, we tested whether groupnest-founding in the fire ant Solenopsis invicta improved theability of queens to survive attacks by mature colonies. Inthe laboratory, queens in groups of three were more likely thansolitary queens to survive attacks by workers of the nativefire ant Solenopsis geminata. When newly mated queens were establishedexperimentally in the field, workers from mature S. invictacolonies caused the majority of queen deaths. Queens in groupsof two, but not in groups of four, had higher survival ratesthan did solitary queens during the period between colony establishmentand the appearance of the first workers. The advantage of cooperativedefense approximately counterbalanced the disadvantages causedby competition within foundress associations of two to threequeens. Previous studies have shown that colonies founded bymultiple queens produce larger worker populations than coloniesfounded by solitary queens; however, experimentally increasingworker number in incipient colonies had no effect on colonysurvival in the field.     

Hazards of insecticides to the bumble bees Bombus impatiens (Hymenoptera: Apidae) foraging on flowering white clover in turf

Insecticides used on turf are sometimes applied to areas with flowering weeds that attract honey bees and native pollinators. We tested residual effects of such treatments on colony vitality and behavior of the bumble bees Bombus impatiens Cresson foraging on turf containingwhite clover, Trifolium repens L. Imidacloprid, a syst emic chloronicotinyl used for preventive control of root-feeding grubs, was applied as granules, followed by irrigation, or sprayed as a wettable powder, with or without irrigation. Hives were confined on the plots in large field cages after residues had dried and colony vitality (i.e., numbers of brood, workers, and honey pots, and weights of queens, workers, and whole colonies with hives) was evaluated after 28-30 d. Workers' foraging activity and defensive response to an aggressive stimulus also were evaluated. In another test, weedy turf was sprayed with chlorpyrifos, carbaryl, or cyfluthrin at labeled rates for surface-feeding pests. Bee colonies were confined on the plots after residues had dried, with effects on colony vitality evaluated after 14 d. Finally, foraging activity of wild bumble bees was monitored on open plots to determine if insecticide-treated areas were avoided. Imidacloprid granules, and imidacloprid sprays applied with posttreatment irrigation, had no effect on colony vitality or workers' behavior, suggesting that such treatments pose little systemic or residual hazard to bumble bees. In contrast, exposure to dry nonirrigated residues of all of the aforementioned insecticides had severe impact on colony vitality. Foraging workers did not avoid insecticide-treated areas. Means by which turf managers can reduce hazards of insecticide applications to pollinators are discussed.     

Lysosomal cholesterol derived from mildly oxidized low density lipoprotein is resistant to efflux

In atherosclerotic lesions, macrophages store lipid in cytoplasmic inclusions and lysosomes. Regression studies show that lysosomal lipid is not as easily cleared as cytoplasmic inclusion lipid. Macrophages enriched with mildly oxidized low density lipoprotein (oxLDL) accumulate cholesteryl ester (CE) and free cholesterol (FC) in lysosomes. We examined whether lysosomal stores of cholesterol from oxLDL are cleared from THP-1 and mouse macrophages. As in previous studies, oxLDL-enriched THP-1 macrophages accumulated substantial lysosomal cholesterol. Surprisingly, less than 12% of oxLDL-derived lysosomal CE was cleared to efficient FC acceptors (e.g., cyclodextrins, apolipoprotein/phosphatidylcholine vesicles, and fetal bovine serum). Filipin staining showed that lysosomes of oxLDL-treated THP-1 cells contained FC, and despite removal of most of the cell FC (70--80%) by incubation with cyclodextrins, filipin staining of FC in lysosomes did not diminish. Also, when THP-1 macrophages were incubated with [(3)H]CE oxLDL, 73--76% of the [(3)H]CE was retained in a lysosomal hydrolysis resistant pool. In contrast, greater than 90% of acetylated low density lipoprotein (acLDL) [(3)H]CE was hydrolyzed. Furthermore, [(3)H]FC liberated from oxLDL [(3)H]CE was released at a slower rate to cyclodextrins than was [(3)H]FC from acLDL [(3)H]CE. In contrast, only 27% of oxLDL [(3)H]CE was resistant to hydrolysis in mouse macrophages, and the [(3)H]FC generated from oxLDL and acLDL [(3)H]CE was released to cyclodextrins at similar rates. We conclude that lack of hydrolysis and efflux of oxLDL cholesterol is not exclusively inherent in oxLDL, but also requires specific cell factors present in one cell type but not the other.--Yancey, P. G., and W. G. Jerome. Lysosomal cholesterol derived from mildly oxidized low density lipoprotein is resistant to efflux. J. Lipid Res. 2001. 42: 317--327.     

Influence of Aging on Nuclear DNA in Corn Leaves

Leaves of Zea mays L. were selected at a young stage when theyhad accumulated about two-thirds of their maximum chlorophyll,at a mature stage when approximately full dimensions and maximumchlorophyll levels were attained, and following pollen shedwhen lower leaves were dying from the tip. Data show a lossof one-fourth of the nuclear DNA, no effect of aging on eu-and heterochromatin levels and a marked decline in the guanine(G) and cytosine (C) percentages. Although DNA levels mightbe under hormonal control, it is not clear that the loss detectedwould be physiologically influential in aging sequences. Yetthis decline preceded those of leaf nitrogen and chlorophyll. (Received July 7, 1983; Accepted November 23, 1983)     

Bio-magnetostratigraphy and environment of the oldest Eurasian hominoid from the Early Miocene of Engelswies (Germany)

The paleobiogeography of hominoids exhibits a puzzling pattern of migrations between and within Africa and Eurasia. A precise dating of hominoid-bearing localities is therefore essential to reveal the timing, direction and possible causes of dispersals. Here, we present a bio-magnetostratigraphic analysis of the section of Engelswies (Southern Germany, Upper Freshwater Molasse, North Alpine Foreland Basin) where the oldest Eurasian hominoid was found. Our paleomagnetic results reveal a very short normal and a reverse magnetic polarity for the entire section. The polarity record is correlated to the Astronomical Tuned Neogene Time Scale using an integrated stratigraphic approach. This approach follows the chronostratigraphic framework for the Upper Freshwater Molasse, which combines magnetostratigraphy with biostratigraphic, lithostratigraphic and ⁴⁰Ar/³⁹Ar dating results. According to this outcome, the reverse polarity of the Engelswies section most likely correlates to magnetochron C5Cr. The origin of the short normal polarity remains enigmatic. The magnetostratigraphic calibration and the evolutionary level of the Engelswies small mammal fauna suggest an age of 17.1-17.0 Ma (Early Karpatian, Early Miocene) for the oldest Eurasian hominoid, and roughly confirm the estimates of Heizmann and Begun (2001). The estimated age suggests that the first hominoids in Eurasia are contemporaneous with Afro-Arabian afropithecins, and dispersal may have been facilitated by intra-Burdigalian (∼18-17 Ma) sea-level low stands and the beginning of the Miocene Climate Optimum. The paleoclimatic and environmental reconstruction of the Engelswies locality indicates a lakeshore environment near dense subtropical rain forest vegetation, where paratropical temperatures (mean annual temperature around 20 °C) and humid conditions (mean annual precipitation > 1.100 mm) prevailed.