Phenotypic plasticity in two marine snails: constraints superseding life history

In organisms encountering predictable environments, fixed development is expected, whereas in organisms that cannot predict their future environment, phenotypic plasticity would be optimal to increase local adaptation. To test this prediction we experimentally compared phenotypic plasticity in two rocky-shore snail species; Littorina saxatilis releasing miniature snails on the shore, and Littorina littorea releasing drifting larvae settling on various shores, expecting L. littorea to show more phenotypic plasticity than L. saxatilis. We compared magnitude and direction of vectors of phenotypic difference in juvenile shell traits after 3 months exposure to different stimuli simulating sheltered and crab-rich shores, or wave-exposed and crab-free shores. Both species showed similar direction and magnitude of vectors of phenotypic difference with minor differences only between ecotypes of the nondispersing species, indicating that plasticity is an evolving trait in L. saxatilis. The lack of a strong plastic response in L. littorea might be explained by limits rather than costs to plasticity.

Site-specific genetic divergence in parallel hybrid zones suggests nonallopatric evolution of reproductive barriers

The evolution of reproductive isolation in the presence of gene flow is supported by theoretical models but rarely by data. Empirical support might be gained from studies of parallel hybrid zones between interbreeding taxa. We analysed gene flow over two hybrid zones separating ecotypes of Littorina saxatilis to test the expectation that neutral genetic markers will show site-specific differences if barriers have evolved in situ. Distinct ecotypes found in contrasting shore habitats are separated by divergent selection and poor dispersal, but hybrid zones appear between them. Swedish islands formed by postglacial uplift 5000 years ago provide opportunities to assess genetic structure in a recently evolved system. Each island houses a discrete population containing subpopulations of different ecotypes. Hybrid zones between ecotypes may be a product of ecological divergence occurring on each island or a consequence of secondary overlap of ecotypes of allopatric origin that have spread among the islands. We used six microsatellite loci to assess gene flow and genetic profiles of hybrid zones on two islands. We found reduced gene flow over both hybrid zones, indicating the presence of local reproductive barriers between ecotypes. Nevertheless, subpopulations of different ecotypes from the same island were genetically more similar to each other than were subpopulations of the same ecotype from different islands. Moreover, neutral genetic traits separating the two ecotypes across hybrid zones were site-specific. This supports a scenario of in situ origin of ecotypes by ecological divergence and nonallopatric evolution of reproductive barriers.

Trans and surface membrane bound zervamicin IIB: 13C-MAOSS-NMR at high spinning speed

Interactions between (15)N-labelled peptides or proteins and lipids can be investigated using membranes aligned on a thin polymer film, which is rolled into a cylinder and inserted into the MAS-NMR rotor. This can be spun at high speed, which is often useful at high field strengths. Unfortuantely, substrate films like commercially available polycarbonate or PEEK produce severe overlap with peptide and protein signals in (13)C-MAOSS NMR spectra. We show that a simple house hold foil support allows clear observation of the carbonyl, aromatic and C(alpha) signals of peptides and proteins as well as the ester carbonyl and choline signals of phosphocholine lipids. The utility of the new substrate is validated in applications to the membrane active peptide zervamicin IIB. The stability and macroscopic ordering of thin PC10 bilayers was compared with that of thicker POPC bilayers, both supported on the household foil. Sidebands in the (31)P-spectra showed a high degree of alignment of both the supported POPC and PC10 lipid molecules. Compared with POPC, the PC10 lipids are slightly more disordered, most likely due to the increased mobilities of the shorter lipid molecules. This mobility prevents PC10 from forming stable vesicles for MAS studies. The (13)C-peptide peaks were selectively detected in a (13)C-detected (1)H-spin diffusion experiment. Qualitative analysis of build-up curves obtained for different mixing times allowed the transmembrane peptide in PC10 to be distinguished from the surface bound topology in POPC. The (13)C-MAOSS results thus independently confirms previous findings from (15)N spectroscopy [Bechinger, B., Skladnev, D.A., Ogrel, A., Li, X., Rogozhkina, E.V., Ovchinnikova, T.V., O'Neil, J.D.J. and Raap, J. (2001) Biochemistry, 40, 9428-9437]. In summary, application of house hold foil opens the possibility of measuring high resolution (13)C-NMR spectra of peptides and proteins in well ordered membranes, which are required to determine the secondary and supramolecular structures of membrane active peptides, proteins and aggregates.

Assignment of amide proton signals by combined evaluation of HN, NN and HNCA MAS-NMR correlation spectra

In this paper, we present a strategy for the (1)H(N) resonance assignment in solid-state magic-angle spinning (MAS) NMR, using the alpha-spectrin SH3 domain as an example. A novel 3D triple resonance experiment is presented that yields intraresidue H(N)-N-C(alpha) correlations, which was essential for the proton assignment. For the observable residues, 52 out of the 54 amide proton resonances were assigned from 2D ((1)H-(15)N) and 3D ((1)H-(15)N-(13)C) heteronuclear correlation spectra. It is demonstrated that proton-driven spin diffusion (PDSD) experiments recorded with long mixing times (4 s) are helpful for confirming the assignment of the protein backbone (15)N resonances and as an aid in the amide proton assignment.

Oxidant production and immune response after stretch injury in skeletal muscle

PURPOSE

This study investigated oxidant production and associated immune response after acute muscle stretch injury.

METHODS

A standardized single stretch injury was performed on the tibialis anterior (TA) muscle of 36 male New Zealand white rabbits while contralateral control limbs underwent a sham surgery. Animals were sacrificed 0, 4, 12, 24, 48, and 72 h after injury. Potential sites of oxidant production, measured with a dichlorofluorescein (DCF) probe, were evaluated using two separate buffers.

RESULTS

Nonmitochondrial oxidant production measured under basal buffer conditions (0.1 M potassium phosphate) was increased in both injured and control limbs at 24 h (P < 0.01) and was greater in the injured limb at 12 and 48 h (P < 0.01). There was also an interaction of time and injury (P < 0.05). Maximum oxidant production by neutrophils and macrophages, stimulated by the induced buffer (including 1.7 mM ADP, 0.1 mM NADPH, 0.1 mM FeCl3), was increased in both injured and control limbs at 4 h (P < 0.01) and was greater in the injured limb at 48 h (P < 0.01). Myeloperoxidase (MPO) activity, indicating the presence of activated neutrophils, was higher in the injured limb at 4 and 48 h (P < 0.01). The activities of superoxide radical producing and quenching enzymes, xanthine oxidase (XO) and superoxide dismutase (SOD), were elevated at 24 (P < 0.01) and 4 h (P < 0.05), respectively, but showed no difference between injured and control limbs.

CONCLUSION

We conclude that acute muscle stretch injury and the required surgeries to generate the injury result in a biphasic increase in oxidant production in both injured and control limbs, suggesting a systemic immune response. The increase in oxidant production at 4 h may be caused by an increase in activated neutrophils, whereas XO activity may contribute to oxidant generation at 24 h.

Superoxide dismutase gene expression is activated by a single bout of exercise in rat skeletal muscle

The goal of this experiment was to examine contraction-mediated activation of superoxide dismutase (SOD) gene expression in rat superficial vastus lateralis (SVL, type IIb) and deep vastus lateralis (DVL, type IIa) muscles. Female Sprague-Dawley rats were randomly divided into exercise (E) and control (C) groups that were sacrificed at 0, 1, 2, 4, 10, 24, and 48 h (n=6) following an acute bout of treadmill exercise (25 m/min, 5% grade) to exhaustion (running time approximately equals 1 h). Nuclear factor-kappaB (NF-kappaB) in DVL and SVL showed maximal binding at 2 and 10 h respectively, and remained elevated. Activator protein-1 (AP-1) showed maximal binding at 1 h post-exercise, and returned to resting levels at 10 h in both muscles. Mn SOD mRNA abundance in the DVL was increased at 0 (P<0.01), 1, and 2 h (P<0.05) post-exercise, whereas Mn SOD protein was unchanged. In SVL, Mn SOD mRNA abundance was not altered by exercise, whereas Mn SOD protein content was increased at 10 (P<0.05) and 24 h (P<0.075) post-exercise. CuZn SOD mRNA was unchanged with exercise in DVL and SVL, but CuZn SOD protein was elevated 48 h after exercise in both DVL and SVL (P<0.01). Activities of Mn SOD, CuZn SOD and total SOD showed no change with exercise in either muscle examined. These findings indicate that an acute bout of exercise can increase binding of NF-kappaB and AP-1 in both SVL and DVL, which may stimulate Mn SOD mRNA transcription in the more oxidative type DVL muscle. The increased CuZn SOD protein contents seen post-exercise, without increases in mRNA abundance in both DVL and SVL, suggest a translational mechanism in this SOD isoform.

Heteronuclear 2D-correlations in a uniformly [13C, 15N] labeled membrane-protein complex at ultra-high magnetic fields

One- and two-dimensional solid-state NMR experiments on a uniformly labeled intrinsic membrane-protein complex at ultra-high magnetic fields are presented. Two-dimensional backbone and side-chain correlations for a [U-13C, 15N] labeled version of the LH2 light-harvesting complex indicate significant resolution at low temperatures and under Magic Angle Spinning. Tentative assignments of some of the observed correlations are presented and attributed to the alpha-helical segments of the protein, mostly found in the membrane interior.

Superoxide dismutase gene expression in skeletal muscle: fiber-specific effect of age

The influence of ageing on the expression of two superoxide dismutase (SOD) isozymes was examined in three different skeletal muscle fiber types of young (Y, 8 mo) and old (O, 25 mo) rats. Total SOD activity was increased with age in the gastrocnemius (Gas, type II(mix)) and superficial vastus lateralis (SVL, type IIb) but unchanged in the soleus (Sol, type I). The increased SOD activity in SVL was due to increased cytosolic SOD (CuZn SOD), whereas both mitochondrial (Mn SOD) and CuZn SOD activities were increased in Gas. In Sol, Mn SOD activity was significantly increased in aged rats. Mn SOD mRNA level was significantly decreased with age in all three muscles examined, while Mn SOD protein content was not altered. Ageing did not affect CuZn SOD mRNA abundance in any of the muscles, but significantly increased CuZn SOD protein content in aged Gas and Sol. Binding of two redox-sensitive transcription factors, nuclear factor-kappaB (NFkappaB) and activator protein-1 (AP-1) was significantly decreased with age in all three muscle types. These results indicate that increased SOD activity in aged skeletal muscle is not associated with higher levels of gene transcription. Increases in Mn SOD activity seen in aged Gas and Sol are the result of post-translational modification of the enzyme, whereas increases in CuZn SOD activity during ageing may be due to both translational and post-translational control.

Superoxide dismutase gene expression in skeletal muscle: fiber-specific adaptation to endurance training

The effects of endurance training on the enzyme activity, protein content, and mRNA abundance of Mn and CuZn superoxide dismutase (SOD) were studied in various phenotypes of rat skeletal muscle. Female Sprague-Dawley rats were randomly divided into trained (T, n = 8) and untrained (U, n = 8) groups. Training, consisting of treadmill running at 27 m/min and 12% grade for 2 h/day, 5 days/wk for 10 wk, significantly increased citrate synthase activity (P < 0. 01) in the type I (soleus), type IIa (deep vastus lateralis, DVL), and mixed type II (plantaris) muscles but not in type IIb (superficial vastus lateralis, SVL) muscle. Mitochondrial (Mn) SOD activity was elevated by 80% (P < 0.05) with training in DVL. SVL and plantaris muscle in T rats showed 54 and 42% higher pooled immunoreactive Mn SOD protein content, respectively, than those in U rats. However, no change in Mn SOD mRNA level was found in any of the muscles. CuZn SOD activity, protein content, and mRNA level in general were not affected by training, except for a 160% increase in pooled CuZn SOD protein in SVL. Training also significantly increased glutathione peroxidase and catalase activities (P < 0.05), but only in DVL muscle. These data indicate that training adaptations of Mn SOD and other antioxidant enzymes occur primarily in type IIa fibers, probably as a result of enhanced free radical generation and modest antioxidant capacity. Differential training responses of mRNA, enzyme protein, and activity suggest that separate cellular signals may control pre- and posttranslational regulation of SOD.

Endurance training alters antioxidant enzyme gene expression in rat skeletal muscle

The effects of endurance training on gene expression of superoxide dismutase (SOD) and glutathione peroxidase (GPX) were investigated in type 2a and 2b skeletal muscles, as well as heart and liver, in the rat. Female Sprague-Dawley rats (4 months old, 300-320 g) were randomly divided into a trained (T, n = 11) and a control (C, n = 10) group and were pair fed a diet consisting of 66% cornstarch and 34% basal diet that contained all essential nutrients. Training was conducted on a treadmill at 25 m·min-1, 10% grade for 2 h per day, 5 days per week for 10 weeks, resulting in a 79% (p < 0.01) increase in citrate synthase activity in the deep portion of vastus lateralis muscle (DVL, type 2a). Cu-Zn SOD activity was 35% higher (p < 0.01) in DVL of T versus C rats, and Cu-Zn SOD mRNA abundance showed a 125% increase with training (p < 0.05). Cu-Zn SOD protein content was not altered in DVL, but increased significantly (p < 0.05) in the superficial portion of vastus lateralis (type 2b) with training. Trained rats showed a 66% higher (p < 0.05) Mn SOD protein content in DVL, but Mn SOD activity and mRNA abundance were not affected. Training also significantly increased GPX activity by 62% (p < 0.05), without changing its mRNA abundance, in the DVL. Heart and liver showed a 112 and 58% increase (p < 0.01) in Cu-Zn SOD mRNA abundance with training, respectively, but no other training adaptation was detected. These data indicate that endurance training can promote gene expression of muscle antioxidant enzymes in a fiber-specific manner. Training appears to upregulate Cu-Zn SOD mRNA abundance in a number of aerobic tissues, whereas Mn SOD and GPX induction observed in DVL may occur at the post-transcriptional levels.Key words: glutathione peroxidase, mRNA, skeletal muscle superoxide dismutase, training.

Endurance training alters antioxidant enzyme gene expression in rat skeletal muscle

The effects of endurance training on gene expression of superoxide dismutase (SOD) and glutathione peroxidase (GPX) were investigated in type 2a and 2b skeletal muscles, as well as heart and liver, in the rat. Female Sprague-Dawley rats (4 months old, 300-320 g) were randomly divided into a trained (T, n = 11) and a control (C, n = 10) group and were pair fed a diet consisting of 66% cornstarch and 34% basal diet that contained all essential nutrients. Training was conducted on a treadmill at 25 m x min(-1), 10% grade for 2 h per day, 5 days per week for 10 weeks, resulting in a 79% (p < 0.01) increase in citrate synthase activity in the deep portion of vastus lateralis muscle (DVL, type 2a). Cu-Zn SOD activity was 35% higher (p < 0.01) in DVL of T versus C rats, and Cu-Zn SOD mRNA abundance showed a 125% increase with training (p < 0.05). Cu-Zn SOD protein content was not altered in DVL, but increased significantly (p < 0.05) in the superficial portion of vastus lateralis (type 2b) with training. Trained rats showed a 66% higher (p < 0.05) Mn SOD protein content in DVL, but Mn SOD activity and mRNA abundance were not affected. Training also significantly increased GPX activity by 62% (p < 0.05), without changing its mRNA abundance, in the DVL. Heart and liver showed a 112 and 58% increase (p < 0.01) in Cu-Zn SOD mRNA abundance with training, respectively, but no other training adaptation was detected. These data indicate that endurance training can promote gene expression of muscle antioxidant enzymes in a fiber-specific manner. Training appears to upregulate Cu-Zn SOD mRNA abundance in a number of aerobic tissues, whereas Mn SOD and GPX induction observed in DVL may occur at the post-transcriptional levels.

Oxidative stress and aging. Role of exercise and its influences on antioxidant systems

Strenuous exercise is characterized by an increased oxygen consumption and disturbance of intracellular prooxidant-antioxidant homeostasis. At least three biochemical pathways, that is, mitochondrial electron transport chain, xanthine oxidase, and polymorphoneutrophil have been identified as potential sources of intracellular free radical generation during exercise. These deleterious reactive oxygen species pose a serious threat to the cellular antioxidant defense system, such as diminished reserve of antioxidant vitamins and glutathione, and have been shown to cause oxidative damage in exercising and/or exercised muscle and other tissues. However, enzymatic and nonenzymatic antioxidants have demonstrated great versatility and adaptability in response to acute and chronic exercise. The delicate balance between prooxidants and antioxidants during exercise may be altered with aging. Study of the complicated interaction between aging and exercise under the influence of reactive oxygen species would provide more definitive information as to how much aged individuals should be involved in physical activity and whether supplementation of nutritional antioxidants would be desirable.