Nonneutral evolution of tandem repeats in the mitochondrial DNA control region of lagomorphs

The mitochondrial DNA of the European rabbit (Oryctolagus cuniculus) contains a tandem array of 153-bp repeats in the vicinity of the replication origin of the H-stand. Variation among molecules in the number of these repeats results in inter- and intraindividual length polymorphism (heteroplasmy). Generally, in an individual, one predominant molecular type is observed, the others representing a low percentage of the mtDNA content. At the tissue level, we observe a particular distribution of this polymorphism in the gonads compared with liver, kidneys, or brain, implying a relationship between the differentiation status of the cells and the types of new mtDNA molecules which appear and accumulate during lifetime. Similar tandem repeats were also found in the mtDNA noncoding region of European hares (Lepus europaeus), a cottontail (Sylvilagus floridanus), and a pika (Ochotona rufescens). The lengths and the sequences of these units evolve rapidly and in a concerted way, but the number of repeats is maintained in a narrow range, and an internal 20-bp segment is highly conserved. Constraints restrict the evolution of the primary sequence of these repeated units, the number of which is probably controlled by a stabilizing selection.      

Evidence for ongoing introduction of non-native earthworms in the Washington,DC metropolitan area

Earthworm introductions and invasions are ongoing, with significant consequences for ecological characteristics and function where populations of invasive species reach high densities. In North America the influx of people, goods and materials to coastal cities has long been recognized to be related to introduction and establishment of many different invasive organisms. We conducted surveys for soil invertebrates in the Washington, DC area along the Potomac River corridor to examine the influence of historic soil profile disrupting disturbances on the composition of soil invertebrate communities. Here we report three earthworm taxa that either (1) had never been previously reported in North America (Lumbricidae: Helodrilus oculatus), (2) had never been reported from “wild” caught samples in forested soils (Lumbricidae: Eisenia fetida), or (3) represented a notable range expansion for an introduced species (Lumbricidae: Murchieona muldali). All three species reported here have attributes that give reason for concern over their expansion into North American soils, not least of which is their potential for competitive interactions with the remaining native earthworm species.     

Haplotyping cryptic Adélie penguin taxa using low-cost,high-resolution melt curves

Distinguishing morphologically cryptic taxa, by definition, requires genetic data such as DNA sequences. However, DNA sequences may not be obtained easily for taxa from remote sites. Here we provide the details of a high-resolution melt-curve-based method using taxon-specific primers that can distinguish two taxa of Adélie penguins, and that will be usable in Antarctica when combined with some of the newly developed field-deployable thermal cyclers. We suggest that the wider adoption of field-deployable polymerase-chain-reaction-based techniques will enable faster assignation of haplotype to individuals in situ, and so allow the targeting of observations and sample collection to specimens relevant to the research question. Targeting individuals will also reduce the need to repeatedly handle animals and reduce the time and travel required to complete field work.     

Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves

A puzzling population-genetic phenomenon widely reported in allozyme surveys of marine bivalves is the occurrence of heterozygote deficits relative to Hardy-Weinberg expectations. Possible explanations for this pattern are categorized with respect to whether the effects should be confined to protein-level assays or are genomically pervasive and expected to be registered in both protein- and DNA-level assays. Anonymous nuclear DNA markers from the American oyster were employed to reexamine the phenomenon. In assays based on the polymerase chain reaction (PCR), two DNA-level processes were encountered that can lead to artifactual genotypic scorings: (a) differential amplification of alleles at a target locus and (b) amplification from multiple paralogous loci. We describe symptoms of these complications and prescribe methods that should generally help to ameliorate them. When artifactual scorings at two anonymous DNA loci in the American oyster were corrected, Hardy-Weinberg deviations registered in preliminary population assays decreased to nonsignificant values. Implications of these findings for the heterozygote-deficit phenomenon in marine bivalves, and for the general development and use of PCR-based assays, are discussed.      

Purification of adenovirus messenger ribonucleic acid by an aqueous polymer two-phase system.

An aqueous polymer phase system containing 6.3% (w/w) dextran and 3.5% (w/w) poly(ethylene glycol) in 10 mM phosphate buffer (pH 8.0) was developed to select RNA-DNA hybrids from unhybridized RNA. The top phase of this phase system, which contains DNA and the RNA-DNA hybrids, can be used to purify adenovirus messenger RNA both early and late in the infectious cycle. The hybrids can be melted by heat in the top phase and the messenger RNA selected by oligo(dT)cellulose chromatography whereupon the polymers and the DNA percolate and the polyadenylated messenger RNA absorb to the column. The isolated messenger RNA appears to be almost quantitatively recovered at a purity from 70 to 90% depending on the concentration of the specific messenger RNA in the starting material. Early and late viral messenger RNA were selected on the complementary strands of adenovirus DNA according to this procedure.     

Saturable binding to cell membranes of the presynanptic neurotoxin, β-Bungarotoxin

Brief exposure to the protein neurotoxin, β-bungarotoxin, is known to disrupt neuromuscular transmission irreversibly by blocking the release of transmitter from the nerve terminal. This neurotoxin also has a phospholipase A2 activity, although phospholipases in general are not very toxic. To determine if the toxicity of this molecule might result from specific binding to neural tissue, we have looked for high affinity, saturable binding using ¹²⁵I-labeled toxin. At low membrane protein concentration ¹²⁵I-labeled toxin binding was directly proportional to the amount of membrane; at fixed membrane concentration ¹²⁵I-labeled toxin showed saturable binding. It was unlikely that iodination markedly changed the toxin's properties since the iodinated toxin had a comparable binding affinity to that of native toxin as judged by competition experiments. Comparison of toxin binding to brain, liver and red blood cell membranes showed that all had high affinity binding sites with dissociation constants between one and two nanomolar. This is comparable to the concentrations previously shown to inhibit mitochondrial function. However, the density of these sites showed marked variation such that the density of sites was 13.0 pmol/mg protein for a brain membrane preparation, 2.4 pmol/mg for liver and 0.25 pmol/mg for red blood cell membranes.In earlier work we had shown that calcium uptake by brain mitochondria is inhibited at much lower toxin concentrations than is liver mitochondrial uptake. Both liver and brain mitochondria bind toxin specifically, but the density of ¹²⁵I-labeled toxin binding sites on brain mitochondrial prepartions ($\text{3.3 ± 0.3}\text{pmol/mg}$) exceeded by a factor of ten the density on liver mitochondrial preparations ($\text{0.3 ± 0.05}\text{pmol/mg}$). It is also shown that the labeled toxin does not cross synaptosomal membranes, suggesting that mitochondria may not be the site of action of the toxin in vivo. We conclude the β-bungarotoxin is an enzyme which can bind specifically with high affinity to cell membranes.     

Ant genomics sheds light on the molecular regulation of social organization

Ants are powerful model systems for the study of cooperation and sociality. In this review, we discuss how recent advances in ant genomics have contributed to our understanding of the evolution and organization of insect societies at the molecular level.     

Electromyographic changes in work-related myalgia of the trapezius muscle.

In 11 patients, all women, 21-55 years of age, with unilateral work-related myalgia of the trapezius muscle, the right and left trapezius muscles were examined simultaneously for electromyogram (EMG) signs of localized muscle fatigue. All patients were tested with 0-kg hand load for 5 min, holding the arms straight at 90 degrees of elevation in the scapular plane. Only 4 of the patients tolerated exposure to higher load levels. They were tested with 1 kg hand load for 3 min and 2 kg hand load for 2 min, with a period of rest of 30 min between the trials. The EMG mean power frequency (MPF) and root mean square (rms) were calculated. Data were normalized with the initial value as a reference and regression analyses were performed. On both sides a decrease of MPF and an increase of rms were found with increasing time and load, i.e. classical EMG signs of localized muscle fatigue. Compared with the nonaffected side smaller changes were found on the affected side, possibly due to pain inhibition, impaired microcirculation and biochemical changes along the muscle fibres. At 0-kg hand load we found no change of MPF on either side despite subjective feelings of fatigue and pain. We interpreted these findings as an indication of reduced capacity of the affected trapezius muscle to sustain static load with early development of pain-associated local fatigue.