Late Pliocene dinoflagellate cyst and diatom analysis from a high resolution sequence in DSDP Site 594, Chatham Rise, south west Pacific

A high resolution mixed carbonate and siliciclastic sequence from DSDP Site 594 contains a detailed record of climate change in the late Pliocene. The sequence can be accurately dated by the LAD of Nitzschia weaveri, the LAD of Thalassiosira insigna, the LAD of T. vulnifica and the LAD of T. kolbei diatom datums. Carbonate content and δ¹⁸O signatures provide added resolution and place the sequence between isotope stages 100 and 92.The sequence contains well-preserved and diverse dinoflagellate cyst floras. Use of principal component (PCA) and canonical correspondence analyses (CCA) identifies changes in the assemblages that principally reflect warming and cooling trends. Species associated with warmer climates included Impagidinium patulum, I. paradoxum and I. sp. cf. paradoxum while those from cooler climates include Invertecysta tabulata and I. velorum. CCA is shown to be a valuable method of determining the past environmental preferences of extinct species such as I. tabulata.     

Allosteric sensitivity in hemoglobin at the alpha-subunit N-terminus studied by hydrogen exchange

Allosteric structure change in human hemoglobin was studied by hydrogen-tritium-exchange methods. The functional labeling method used takes advantage of the change in H-exchange rate at allosterically involved sites to selectively label, with tritium, H-exchange sites that are fast in one protein state and slow in another. The position of the labeled sites can then be located by the medium-resolution fragmentation-separation method. These methods reveal 5 allosterically sensitive, H-bonded, peptide NH's within the first 12 residues of the alpha chain. All five exchange with solvent protons at similar rates in deoxyhemoglobin (T form), and all shift to a new rate, about 30-fold faster, in the liganded protein (R) form. This indicates a decrease in structural stability at the alpha-chain N-terminus in going from the T to the R form, consistent with the loss of stabilizing interactions in that segment. The results indicate a loss of perhaps 2 kcal/mol in stabilization free energy and thus document a significant role for changes at the alpha-chain N-terminus in the allosteric transition.     

The mutagenic effect of benzene, toluene and xylene studied by the SCE technique.

In experiments in vitro, neither benzene, toluene nor xylene changed the number of sister-chromatid exchanges (SCEs) or the number of chromosomal aberrations in human lymphocytes. Toluene and xylene caused a significant cell growth inhibition which was not observed with benzene in the same concentrations.     

Shape variation in the rough periwinkle Littorina saxatilis on the west and south coasts of Britain

Variation in the shape of the shell in Littorina saxatilis Olivi has been shown to be due largely to the same variables on both the west and the south coasts of Britain, and it exhibits various clines. Two important aspects are the size of the aperture, which becomes relatively larger from the Isle of Man southwards to Cornwall and eastwards from Devon to the Isle of Wight, and the jugosity of the shell, which increases with distance from Cornwall both northwards as far as the Isle of Man and eastwards as far as Kent. Superimposed on the clines are domains of shape, notably one in Lewis/Harris, where the shells have a relatively large aperture, which is long and narrow, coupled with a rather globose second whorl. The local and geographical aspects of shell shape variation are discussed.     

Interdomain compactization in human tyrosyl-tRNA synthetase studied by the hierarchical rotations technique

Aminoacyl-tRNA synthetases are key enzymes of protein biosynthesis which usually possess multidomain structures. Mammalian tyrosyl-tRNA synthetase is composed of two structural modules: N-terminal catalytic core and an EMAPII-like C-terminal domain separated by long flexible linker. The structure of full-length human cytoplasmic tyrosyl-tRNA synthetase is still unknown. The structures of isolated N-terminal and C-terminal domains of the protein are resolved, but their compact packing in a functional enzyme is a subject of debates. In this work we studied putative compactization of the N- and C-terminal modules of human tyrosyl-tRNA synthetase by the coarse-grained hierarchical rotations technique (HIEROT). The large number of distinct types of binding interfaces between N- and C-terminal modules is revealed in the absence of enzyme substrates. The binding propensities of different residues are computed and several binding "hot spots" are observed on the surfaces of N and C modules. These results could be used to govern atomistic molecular dynamics simulations, which will sample preferable binding interfaces effectively.     

NADH- and H2-oxidation in hydrogen bacteria studied by respiratory chain inhibitors

Summary The oxidation of hydrogen and NADH by membrane fractions of two autotrophically grown hydrogen bacteria,Pseudomonas facilis and strain14 g, both lacking a hydrogen dehydrogenase, was studied by difference-spectrophotometric and manometric methods. The spectrophotometric data did not support the existence of two separate electron transport pathways for both the substrates. However, from the effect of rotenone, antimycin A, BAL, and HQNO on the oxygen uptake rate with H₂ or NADH as substrates, separate pathways could be proposed: in strain14 g at least tocytochrome b and inP. facilis at least tocytochrome c.     

Changes in the model membrane structure induced by ribonuclease and lysozyme studied by the fluorescent probe technique

Using fluorescent probes DSM and DSP-12, the effect of ribonuclease and lysozyme on the structural state of liposomes composed of phosphatidylcholine and diphosphatidylglycerol was studied. A correlation between the changes in probe quantum yield and the amount of protein-bound lipids was established. It is assumed that the formation of protein-lipid complexes increases the packing density of lipids and restricts their mobility. As the content of diphosphatidylglycerol in the lipid bilayer increases, the condensing effect of proteins becomes more pronounced.     

Lactose digestion capacity in Tokelauans: a case for the role of gene flow and genetic drift in establishing the lactose absorption allele in a Polynesian population

Throughout the Pacific, lactose absorption occurs at rates of 0-46%. Most authors explain the current rate of lactose absorption in the Pacific in terms of gene flow with Europeans. However, researchers have not been able to determine the exact historical circumstances of the introduction of the lactose absorption gene. The availability of genealogical material, historical information, and mal/absorption frequencies for Tokelau (a Polynesian population) presents a unique opportunity to examine the role of gene flow in establishing lactose absorption in Pacific isolates. In an earlier study, Cheer and Allen ([1997] Am. J. Hum. Biol. 93:1-34) determined lactose digestion capacities for 58 Tokelauans. In the current study, we constructed pedigrees for the same 58 individuals, using the Tokelau Island Migrant Study genealogies (Wessen et al. [1992]). Results indicated that 8 of 13 lactose-absorbing individuals have European ancestors, compared with only 4 of 35 lactose malabsorbers (Chi(2) = 15.75, P < 0.01). Six lactose-absorbing individuals have either American or Portuguese ancestors dating back to the mid-1800s. Historical data were used to establish the contribution of Portuguese and American genetic material to the Tokelau population following massive depopulation after the Peruvian slave raids of 1863. This study provides clear evidence for the role of a population bottleneck followed by gene flow and genetic drift in establishing lactose absorption in the Tokelau population. Furthermore, it is the first study of a Pacific population to directly link lactose absorption with gene flow.     

Science and Practice in NRM: Insights from connectivity restoration in the south west slopes of NSW

Interactions between landholders, practitioners and research scientists have greatly influenced landscape restoration activities in South‐eastern Australia. Vegetation connectivity projects undertaken by Holbrook Landcare Network in the Slopes to Summit (S2S) region of South‐eastern Australia have benefitted from the input of both scientists and practitioners. This paper explores what factors support an evidence‐informed restoration outcome, what constrains this and what we can learn from this case.     

Frequency and distribution of chiasmata in Syrian hamster spermatocytes studied by the BrdU antibody technique

The frequency and distribution of chiasmata and the nature of terminal associations was re-examined in Syrian hamster spermatocytes using the 5-bromo-2-deoxyuridine (BrdU) antibody technique (BAT) for differential chromatid labelling. Differential chromatid substitution was achieved by BrdU incorporation at the penultimate pre-meiotic S-phase followed by one of three different staining protocols: (i) fluorescence plus Giemsa (FPG), (ii) acridine orange staining or (iii) BAT. For analysis of chiasmata frequency and localization in the diplotene/diakinesis stages the resolution of FPG and acridine orange staining was comparable to that of BAT. In metaphase II chromosomes BAT was more informative than FPG and acridine orange staining and revealed small, terminal crossover exchanges. This finding proves that many terminal associations of meiotic chromosomes actually represent chiasmata at the end of the first meiotic division. Some crossover exchanges were localized in the constitutive heterochromatin of autosomes. Using BAT we also detected crossover exchanges in close vicinity to each other. This observation is reminiscent of the fact that crossing over interference means a reduction in frequency and does not imply total inhibition.     

Meiotic chromosome pairing in Stethophyma grossum spermatocytes studied by a surface-spreading and silver-staining technique

Spermatocytes of Stethophyma grossum were prepared for light microscope examination by a surface-spreading and silver-staining technique adapted with very little modification from a mammalian procedure. Very clear preparations of a variety of prophase I stages were obtained which revealed many details of chromosome and nuclear organisation. These observations and preliminary observations on two other grasshopper species demonstrate the ready applicability of these techniques to Orthopteran spermatocytes. A detailed study of six pachytene stage spermatocytes gave conclusive confirmation that three bivalents achieve full pairing in male meiosis of Stethophyma grossum, the other eight bivalents being partially paired at their procentric ends only.     

Interfacial positioning and stability of transmembrane peptides in lipid bilayers studied by combining hydrogen/deuterium exchange and mass spectrometry.

Nano-electrospray ionization mass spectrometry (ESI-MS) was used to analyze hydrogen/deuterium (H/D) exchange properties of transmembrane peptides with varying length and composition. Synthetic transmembrane peptides were used with a general acetyl-GW(2)(LA)(n)LW(2)A-ethanolamine sequence. These peptides were incorporated in large unilamellar vesicles of 1,2-dimyristoyl-sn-glycero-3-phosphocholine. The vesicles were diluted in buffered deuterium oxide, and the H/D exchange after different incubation times was directly analyzed by means of ESI-MS. First, the influence of the length of the hydrophobic Leu-Ala sequence on exchange behavior was investigated. It was shown that longer peptide analogs are more protected from H/D exchange than expected on the basis of their length with respect to bilayer thickness. This is explained by an increased protection from the bilayer environment, because of stretching of the lipid acyl chains and/or tilting of the longer peptides. Next, the role of the flanking tryptophan residues was investigated. The length of the transmembrane part that shows very slow H/D exchange was found to depend on the exact position of the tryptophans in the peptide sequence, suggesting that tryptophan acts as a strong determinant for positioning of proteins at the membrane/water interface. Finally, the influence of putative helix breakers was studied. It was shown that the presence of Pro in the transmembrane segment results in much higher exchange rates as compared with Gly or Leu, suggesting a destabilization of the alpha-helix. Tandem MS measurements suggested that the increased exchange takes place over the entire transmembrane segment. The results show that ESI-MS is a convenient technique to gain detailed insight into properties of peptides in lipid bilayers by monitoring H/D exchange kinetics.     

Pathology of tissue loss (white syndrome) in Acropora sp. corals from the Central Pacific

We performed histological examination of 69 samples of Acropora sp. manifesting different types of tissue loss (Acropora White Syndrome-AWS) from Hawaii, Johnston Atoll and American Samoa between 2002 and 2006. Gross lesions of tissue loss were observed and classified as diffuse acute, diffuse subacute, and focal to multifocal acute to subacute. Corals with acute tissue loss manifested microscopic evidence of necrosis sometimes associated with ciliates, helminths, fungi, algae, sponges, or cyanobacteria whereas those with subacute tissue loss manifested mainly wound repair. Gross lesions of AWS have multiple different changes at the microscopic level some of which involve various microorganisms and metazoa. Elucidating this disease will require, among other things, monitoring lesions over time to determine the pathogenesis of AWS and the potential role of tissue-associated microorganisms in the genesis of tissue loss. Attempts to experimentally induce AWS should include microscopic examination of tissues to ensure that potentially causative microorganisms associated with gross lesion are not overlooked.     

The effect of anaesthetics on protein conformation in membranes as studied by the spin-labelling technique

The effect of general and local anaesthetics was studied on the membrane components (proteins and lipids) of frog sciatic nerve using the spin-labelling technique. A rapid and effective method was developed to incorporate fatty acid labels into the lipid regions and to attach the maleimide spin labels to the thiol sites of the proteins of the membrane. On the basis of the rotational correlation time of the attached maleimide spin labels, at least three different protein domains were identified. One part of the labels has a preferred orientation with respect to the axis of the nerve fibre. The effect of halothane and of local anaesthetics such as lidocaine and tetracaine, which influence primarily the lipid regions of the membrane, is efficiently transferred to the spin-labelled membrane proteins via strong lipid-protein interaction. The results support the concept that the architecture and the physiological activity of the membrane-bound proteins are sensitive to changes in the physical state of membrane lipids.     

Comparison of case fatality in south Asian and white patients after acute myocardial infarction: observational study.

OBJECTIVE--To compare mortality in south Asian (Indian, Pakistani, and Bangladeshi) and white patients in the six months after hospital admission for acute myocardial infarction. DESIGN--Observational study. SETTING--District general hospital in east London. PATIENTS--149 south Asian and 313 white patients aged < 65 years admitted to the coronary care unit with acute myocardial infarction from 1 December 1988 to 31 December 1992. MAIN OUTCOME MEASURE--All cause mortality in the first six months after myocardial infarction. RESULTS--The admission rate in the south Asians was estimated to be 2.04 times that in the white patients. Most aspects of treatment were similar in the two groups, except that a higher proportion of the south Asians received thrombolytic drugs (81.2% v 73.8%). After adjustment for age, sex, previous myocardial infarction, and treatment with thrombolysis or aspirin, or both, the south Asians had a poorer survival over the six months from myocardial infarction (hazard ratio 2.02 (95% confidence interval 1.14 to 3.56), P = 0.018), but a substantially higher proportion were diabetic (38% v 11%, P < 0.001), and additional adjustment for diabetes removed much of their excess risk (adjusted hazard ratio 1.26 (0.68 to 2.33), P = 0.47). CONCLUSION--South Asian patients had a higher risk of admission with myocardial infarction and a higher risk of death over the ensuing six months than the white patients. The higher case fatality among the south Asians, largely attributable to diabetes, may contribute to the increased risk of death from coronary heart disease in south Asians living in Britain.