RIBOSOMAL-DNA,MITOCHONDRIAL-DNA,CHROMOSOMAL, AND ALLOZYMIC STUDIES ON A CONTACT ZONE IN THE POCKET GOPHER,GEOMYS

We studied 75 individuals of the Plains pocket gopher, Geomys bursarius, from eastern New Mexico, where the subspecies major and knoxjonesi hybridize. Each individual was examined for chromosome number, ribosomal DNA, mitochondrial DNA, and three protein systems for which reference parental populations were fixed for alternative alleles. Twenty individuals were indistinguishable from parental major, 14 individuals were indistinguishable from parental knoxjonesi, and 41 individuals had genotypes composed of combinations of character states that distinguish the two parental types. The parental types appear to represent discrete genetic entities that have restricted introgression across a narrow hybrid zone (width approximately 3 km, using the 20/80 criterion). Parental types overlap in geographic distribution near the center of the zone, and changes in mitochondrial DNA and the five nuclear markers are concordant across the zone. It is probable that there is premating isolation between knoxjonesi males and major females. The frequencies of individuals with certain genotypic combinations within our sample imply differential reproductive success of certain genotypes. We propose that F₁'s and highly heterozygous males are sterile and that hybrid females are less fertile than parental females. These postmating factors, along with premating isolation for one of the reciprocal crosses, probably account for the restriction of gene flow across the contact zone. The structure of the zone can be explained by the “dynamic equilibrium” model.     

First chemical synthesis of a scorpion alpha-toxin affecting sodium channels: the Aah I toxin of Androctonus australis hector.

Aah I is a 63-residue alpha-toxin isolated from the venom of the Buthidae scorpion Androctonus australis hector, which is considered to be the most dangerous species. We report here the first chemical synthesis of Aah I by the solid-phase method, using a Fmoc strategy. The synthetic toxin I (sAah I) was renatured in DMSO-Tris buffer, purified and subjected to thorough analysis and comparison with the natural toxin. The sAah I showed physico-chemical (CD spectrum, molecular mass, HPLC elution), biochemical (amino-acid composition, sequence), immunochemical and pharmacological properties similar to those of the natural toxin. The synthetic toxin was recognized by a conformation-dependent monoclonal anti-Aah I antibody, with an IC50 value close to that for the natural toxin. Following intracerebroventricular injection, the synthetic and the natural toxins were similarly lethal to mice. In voltage-clamp experiments, Na(v) 1.2 sodium channel inactivation was inhibited by the application of sAah I or of the natural toxin in a similar way. This work describes a simple protocol for the chemical synthesis of a scorpion alpha-toxin, making it possible to produce structural analogues in time.     

Soil 13C–15N dynamics in an N2-fixing clover system under long-term exposure to elevated atmospheric CO2

Reduced soil N availability under elevated CO₂ may limit the plant's capacity to increase photosynthesis and thus the potential for increased soil C input. Plant productivity and soil C input should be less constrained by available soil N in an N₂‐fixing system. We studied the effects of Trifolium repens (an N₂‐fixing legume) and Lolium perenne on soil N and C sequestration in response to 9 years of elevated CO₂ under FACE conditions. ¹⁵N‐labeled fertilizer was applied at a rate of 140 and 560 kg N ha^?1 yr^?1 and the CO₂ concentration was increased to 60 Pa pCO₂ using ¹³C‐depleted CO₂. The total soil C content was unaffected by elevated CO₂, species and rate of ¹⁵N fertilization. However, under elevated CO₂, the total amount of newly sequestered soil C was significantly higher under T. repens than under L. perenne. The fraction of fertilizer‐N (f_N) of the total soil N pool was significantly lower under T. repens than under L. perenne. The rate of N fertilization, but not elevated CO₂, had a significant effect on f_N values of the total soil N pool. The fractions of newly sequestered C (f_C) differed strongly among intra‐aggregate soil organic matter fractions, but were unaffected by plant species and the rate of N fertilization. Under elevated CO₂, the ratio of fertilizer‐N per unit of new C decreased under T. repens compared with L. perenne. The L. perenne system sequestered more ¹⁵N fertilizer than T. repens: 179 vs. 101 kg N ha^?1 for the low rate of N fertilization and 393 vs. 319 kg N ha^?1 for the high N‐fertilization rate. As the loss of fertilizer‐¹⁵N contributed to the ¹⁵N‐isotope dilution under T. repens, the input of fixed N into the soil could not be estimated. Although N₂ fixation was an important source of N in the T. repens system, there was no significant increase in total soil C compared with a non‐N₂‐fixing L. perenne system. This suggests that N₂ fixation and the availability of N are not the main factors controlling soil C sequestration in a T. repens system.     

Sex differences in heritability of BMI: a comparative study of results from twin studies in eight countries.

Body mass index (BMI), a simple anthropometric measure, is the most frequently used measure of adiposity and has been instrumental in documenting the worldwide increase in the prevalence of obesity witnessed during the last decades. Although this increase in overweight and obesity is thought to be mainly due to environmental changes, i.e., sedentary lifestyles and high caloric diets, consistent evidence from twin studies demonstrates high heritability and the importance of genetic differences for normal variation in BMI. We analysed self-reported data on BMI from approximately 37,000 complete twin pairs (including opposite sex pairs) aged 20-29 and 30-39 from eight different twin registries participating in the GenomEUtwin project. Quantitative genetic analyses were conducted and sex differences were explored. Variation in BMI was greater for women than for men, and in both sexes was primarily explained by additive genetic variance in all countries. Sex differences in the variance components were consistently significant. Results from analyses of opposite sex pairs also showed evidence of sex-specific genetic effects suggesting there may be some differences between men and women in the genetic factors that influence variation in BMI. These results encourage the continued search for genes of importance to the body composition and the development of obesity. Furthermore, they suggest that strategies to identify predisposing genes may benefit from taking into account potential sex specific effects.     

Response of Daphnia to substances released from crowded congeners and conspecifics

The effects of chemicals released from crowded congeners andconspecifics on life history parameters of the freshwater zooplanktersDaphnia cucullata and Daphnia pulex were examined. Length andage at maturity of D. pulex were affected by crowding chemicals.Reproduction was lower in crowded medium, and ephippia wereproduced. Newborn D. pulex in crowded medium were significantlylonger than the controls. The intrinsic rate of population increaseof D. pulex was 14 and 25% lower than the control when exposedto crowded medium from D. cucullata and D. pulex, respectively.Neither urea nor ammonia (at 1 mg l^-1) seemed to be responsiblefor these effects in D. pulex. In D. cucullata, no significanteffect of crowding infochemicals on length and age at maturitywas found. However, crowding chemicals reduced reproduction.No ephippia were produced in crowded medium, but up to 83% non-developingeggs were observed in D. cucullata. Newborns were similarlysized in crowded and standard medium. The intrinsic rate ofpopulation increase of D. cucullata was 44 and 96% lower thanthe control when exposed to crowded medium from D. cucullataand D. pulex, respectively. Clearance rates of D. pulex weresignificantly reduced in crowded media compared with standardmedium, which could partly explain why the animals exposed tocrowding chemicals reacted as if they were food limited.     

Characterization of the bioactive conformation of the C-terminal tripeptide Gly-Leu-Met-NH2 of substance P using [3-prolinoleucine10]SP analogues.

Residue Leu10 of substance P (SP) is critical for NK-1 receptor recognition and agonist activity. In order to probe the bioactive conformation of this residue, cis- and trans-3-substituted prolinoleucines were introduced in position 10 of SP. The substituted SP analogues were tested for their affinity to human NK-1 receptor specific binding sites (NK-1M and NK-1m) and their potency to stimulate adenylate cyclase and phospholipase C in CHO cells transfected with the human NK-1 receptor. [trans-3-prolinoleucine10]SP retained affinity and potency similar to SP whereas [cis-3-prolinoleucine10]SP shows dramatic loss of affinity and potency. To analyze the structural implications of these biological results, the conformational preferences of the SP analogues were analyzed by NMR spectroscopy and minimum-energy conformers of Ac-cis-3-prolinoleucine-NHMe, Ac-trans-3-prolinoleucine-NHMe and model dipeptides were generated by molecular mechanics calculations. From NMR and modeling studies it can be proposed that residue Leu10 of SP adopts a gauche(+) conformation around the chi1 angle and a trans conformation around the chi2 angle in the bioactive conformation. Together with previously published results, our data indicate that the C-terminal SP tripeptide should preferentially adopt an extended conformation or a PPII helical structure when bound to the receptor.     

A misfolded form of 5S rRNA is complexed with the Ro and La autoantigens.

In both vertebrate and invertebrate cells, the 60-kDa Ro autoantigen is bound to small cytoplasmic RNAs known as Y RNAs. In Xenopus oocytes, the 60-kDa Ro protein is also complexed with a class of 5S rRNA precursors that contain internal mutations. Because these 5S rRNA precursors are processed inefficiently and degraded eventually, the Ro protein may function in a quality control pathway for 5S rRNA biosynthesis. We have investigated the sequence and secondary structure determinants in the mutant 5S rRNAs that confer binding by the 60-kDa Ro protein. The mutant 5S rRNAs fold to form an alternative helix that is required for recognition by the 60-kDa Ro protein. Mutations that disrupt the alternative helix eliminate Ro protein binding, whereas compensatory changes that restore the helix are bound efficiently by the Ro protein. When the structure of the mutant RNA was probed using dimethylsulfate and oligonucleotide-directed RNase H cleavage, the results were consistent with the formation of the alternative structure. The La protein, which is also complexed with the mutant 5S rRNA precursors, protects similar sequences from nuclease digestion as does the 60-kDa Ro protein. Thus, the binding sites for these two proteins are either nearby on the RNA, or the two proteins may be complexed through protein-protein interactions. When the human Ro protein is expressed in the yeast Saccharomyces cerevisiae, the protein binds wild-type 5S rRNA precursors, suggesting that a population of wild-type precursors also folds into the alternative structure.