Determinants of peak muscle power: effects of age and physical conditioning

The relationships between absolute peak muscle power (W _peak), muscle cross sectional area (CSA_tot, i.e. the sum of both thigh and calf CSA) and muscle high energy phosphate concentration (adenosine 5-triphosphate [ATP] and phosphocreatine concentrations [PC]) were studied in 47 subjects classified into five groups: A, 10 sedentary (S) subjects aged 20–35 years; B, 9 S aged 35–50 years; C, 9 S aged more than 50 years; D, 13 children aged 8–13 years; and E, 6 athletes (top level volleyball players) aged 24 (SD 3) years. The W _peak was measured during a maximal vertical high jump off both feet on a force platform. The CSA_tot was measured anthropometrically. The [ATP] and [PC] were determined by ³¹Phosphorus nuclear magnetic resonance spectroscopy. The W _peak decreased with age, was 65% lower in D than in A, and 43% higher in E than in A. The CSA_tot did not vary with age, was 45% smaller in D than in A, and 15% greater in E than in A. The [ATP] and [PC] were essentially the same in all groups. The changes observed in W _peak were only partially accounted for by changes in CSA_tot. Therefore, in addition to the variables investigated, other factors appear to have been involved in the determination of W _peak with increasing age and training. An important role may be played by hormonal, particularly at puberty, and neural factors.     

Anthocorid predators learn to associate herbivore-induced plant volatiles with presence or absence of prey

We investigated how the plant‐inhabiting, anthocorid predator, Anthocoris nemoralis, copes with variation in prey, host plant and associated herbivore‐induced plant volatiles and in particular whether the preference for these plant odours is innate or acquired. We found a marked difference between the olfactory response of orchard‐caught predators and that of their first generation reared on flour moth eggs in the laboratory, i.e. under conditions free of herbivory‐induced volatiles. Whereas the orchard‐caught predators preferred odour from psyllid‐infested pear leaves, when offered against clean air in a Y‐tube olfactometer, the laboratory‐reared first generation of (naive) predators did not. The same difference was found when a single component (methyl salicylate) of the herbivore‐induced plant volatiles was offered against clean air. After experiencing methyl salicylate with prey, however, the laboratory‐reared predators showed a pronounced preference for this volatile. This acquired preference did not depend on whether the volatile had been experienced in the juvenile period or in the adult phase, but it did depend on whether it had been offered in presence or absence of prey. In the first case, they were attracted to the plant volatile in subsequent olfactometer experiments, but when the volatile had been offered during a period of prey deprivation, the predators were not attracted. We conclude that associative learning is the most likely mechanism underlying acquired odour preference.     

Quantitative PCR method to detect a 13-kb deletion in the MURR1 gene associated with copper toxicosis and HIV-1 replication

The recently discovered locus for copper toxicosis (CT) in Bedlington terriers (BT) has a 13-kb deletion enveloping the 187-bp exon-2 of the MURR1 gene. This MURR1 gene is not only involved with biliary copper excretion but also associated with HIV-1 replication. The microsatellite C04107 lying in an intron of the MURR1 gene is highly associated with the disease but shows haplotype diversity. The only solid molecular test for the disease is by showing the deletion in exon-2 in cDNA in liver tissue; this test is not robust on RNA from peripheral leukocytes because of their low MURR1 expression level. Because of these drawbacks, we developed a new quantitative PCR (Q-PCR) protocol. Here we show that the MURR1 exon-2/exon-3 ratio measured by Q-PCR on genomic DNA correlates perfectly with the microsatellite marker and with RT-PCR data from blood samples, buccal swabs, and liver biopsies. In view of the important role of MURR1 in cells of many tissues, this new test has a wide range of applications in comparative biomedical research. Furthermore, Q-PCR on DNA may be a new tool in general to analyze mutations that cannot be approached by standard methods.Robert P. Favier and Bart Spee contributed equally to this work.     

CD36 deficiency increases insulin sensitivity in muscle,but induces insulin resistance in the liver in mice

CD36 (fatty acid translocase) is involved in high-affinity peripheral fatty acid uptake. Mice lacking CD36 exhibit increased plasma free fatty acid and triglyceride (TG) levels and decreased glucose levels. Studies in spontaneous hypertensive rats lacking functional CD36 link CD36 to the insulin-resistance syndrome. To clarify the relationship between CD36 and insulin sensitivity in more detail, we determined insulin-mediated whole-body and tissue-specific glucose uptake in CD36-deficient (CD36-/-) mice. Insulin-mediated whole-body and tissue-specific glucose uptake was measured by d-[3H]glucose and 2-deoxy-d-[1-3H]glucose during hyperinsulinemic clamp in CD36-/- and wild-type control littermates (CD36+/+) mice. Whole-body and muscle-specific insulin-mediated glucose uptake was significantly higher in CD36-/- compared with CD36+/+ mice. In contrast, insulin completely failed to suppress endogenous glucose production in CD36-/- mice compared with a 40% reduction in CD36+/+ mice. This insulin-resistant state of the liver was associated with increased hepatic TG content in CD36-/- mice compared with CD36+/+ mice (110.9 +/- 12.0 and 68.9 +/- 13.6 microg TG/mg protein, respectively). Moreover, hepatic activation of protein kinase B by insulin, measured by Western blot, was reduced by 54%. Our results show a dissociation between increased muscle and decreased liver insulin sensitivity in CD36-/- mice.     

Coping with low nutrient availability and inundation: root growth responses of three halophytic grass species from different elevations along a flooding gradient

We describe the responses of three halophytic grass species that dominate the low (Spartina anglica), middle (Puccinellia maritima) and high (Elymus pycnanthus) parts of a salt marsh, to soil conditions that are believed to favour contrasting root-growth strategies. Our hypotheses were: (1) individual lateral root length is enhanced by N limitations in the soil but restricted by oxygen limitations, (2) the density of root branching within a species is inversely related to the length of the lateral roots, and (3) species from high elevations (i.e. the driest parts of a marsh) are the most responsive to changing soil conditions. Plant growth responses and soil parameters showed that the contrasting but uniformly applied soil treatments were effective. All three species showed a small but significant shift towards a finer root diameter distribution when N was limiting, partly because of the finer diameters of the laterals (Elymus and Spartina) and partly because of increased length of individual 1st-order laterals (Elymus and Puccinellia). The increased length of the 1st-order laterals of Elymus and Puccinellia grown under low N indicates that the first part of hypothesis 1 may be true. However, lack of effect of flooding and reduced soil conditions lead us to reject the second part of hypothesis 1. Hypothesis 2 was rejected for these three halophytes, as the branch density of 1st- and 2nd-order laterals appears to be controlled by other factors than length of individual laterals. Hypothesis 3 may be true for specific root characteristics (e.g. length of individual 1st-order laterals), but cannot be generalised (e.g. branch density and topological index). In conclusion, the present data on root growth in contrasting but homogeneous soil conditions indicate that morphological responsiveness of the root systems of these halophytic grass species is limited, regardless of their location along the elevational gradient.     

The multi-functional SNARE protein Ykt6 in autophagosomal fusion processes

Autophagy is a degradative pathway in which cytosolic material is enwrapped within double membrane vesicles, so-called autophagosomes, and delivered to lytic organelles. SNARE (Soluble N-ethylmaleimide sensitive factor attachment protein receptor) proteins are key to drive membrane fusion of the autophagosome and the lytic organelles, called lysosomes in higher eukaryotes or vacuoles in plants and yeast. Therefore, the identification of functional SNARE complexes is central for understanding fusion processes and their regulation. The SNARE proteins Syntaxin 17, SNAP29 and Vamp7/VAMP8 are responsible for the fusion of autophagosomes with lysosomes in higher eukaryotes. Recent studies reported that the R-SNARE Ykt6 is an additional SNARE protein involved in autophagosome-lytic organelle fusion in yeast, Drosophila, and mammals. These current findings point to an evolutionarily conserved role of Ykt6 in autophagosome-related fusion events. Here, we briefly summarize the principal mechanisms of autophagosome-lytic organelle fusion, with a special focus on Ykt6 to highlight some intrinsic features of this unusual SNARE protein.