Parasitic infection and developmental stability: fluctuating asymmetry in Gammarus pulex infected with two acanthocephalan species

Several studies have reported a negative association between developmental stability and parasitic infection. However, the host-parasite associations examined so far consist only of a limited number of parasite taxa, and developmental stability was appraised on definitive hosts. The present study examines the association between infection by 2 acanthocephalan parasites. Pomphorhynchus laevis and Polymorphus minutus, and the developmental stability of their common intermediate host Gammarus pulex. Developmental stability was estimated from the fluctuating asymmetry (FA) levels of 6 morphological traits. A positive association was found between FA and infection. Infected gammarids tended to be more asymmetrical than the noninfected ones for an index generated by combining FA scores from 2 characters out of the 6 studied, even though no significant relationships were found between FA levels and parasitic loads. The simultaneous presence of both acanthocephalan species in the same host seems to be associated with increased FA levels of gammarids, but this trend was not statistically significant. For the same characters, males exhibited higher levels of FA than females.     

A protein that specifically recognizes the 3' splice site of mammalian pre-mRNA introns is associated with a small nuclear ribonucleoprotein

Using a protein blotting method for the detection of nucleic acid binding proteins, we have identified in HeLa cell nuclear extracts an intron binding protein (IBP) that selectively recognizes the 3' splice site region of mammalian pre-mRNAs. The binding site was accurately delineated using oligonucleotides complementary to human beta-globin pre-mRNA. It spans the 3' splice site AG dinucleotide and the crucial polypyrimidine stretch upstream, but includes neither the branchpoint nor the lariat structure. Although the technique used here shows that the binding specificity is an intrinsic property of IBP and does not depend on snRNA-pre-mRNA interactions, it comigrates with U5 snRNP and is immunoprecipitated by anti-Sm antibody. This strongly suggests that IBP belongs to U5 snRNP. We propose that it is involved in one of the earliest steps of the splicing reaction by mediating the interaction of U5 snRNP with the 3' splice site.     

Échanges trophallactiques chez un termite supérieur. Contamination par le phosphore radio-actif de la population d'un nid deCubitermes fungifaber

Résumé Des nids deCubitermes fungifaber sont mis en élevage sur de l'humus contaminé (P³²). La radio-activité des Insectes, mesurée après un temps de contact variable, permet de séparer deux catégories d'échanges trophallactiques: les échanges d'aliment régurgité, décelables dès les premières expériences, et les échanges de liquide salivaire apparaissant plus tardivement, 25 à 30 heures après la mise en contact du nid avec l'humus marqué.On n'observe pas de différence significative dans la répartition du P³² selon la zone de prélèvement des échantillons de population, sauf chez des soldats des nids isolés un temps court sur l'humus. La contamination des ouvriers est très rapide et la distribution du phosphore, dans cette caste, hétérogène. Certains ouvriers ne se nourrissent pas directement d'humus pendant le temps de l'expérience; ils reçoivent, ainsi que les soldats, de l'aliment régurgité (stomodéal). La reine est la première contaminée par le liquide salivaire des ouvriers, et sa radio-activité prouve une absorption constante de nourriture. Les ailés proches du vol nuptial sont gavés de salive, ainsi que les soldats blancs. Le couvain, les nymphes de l'avant-dernier stade et le roi ne reçoivent qu'une faible quantité de salive; le roi a un rythme d'alimentation lent et peu de besoins; les nymphes ont, sans doute, recours à un autre mode d'alimentation pendant l'avant-dernier stade.Ces données seront complétées par l'étude particulière des différentes castes.

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Summary Nests ofCubitermes fungifaber were reared on labelled humus (P³²) The radioactivity of the insects measured after varying periods of contact enabled two categories of trophallactic exchanges to be discerned: an exchange of regurgitated food that is percieved at the early stage of the experiment, and an exchange of salivary fluid that appears much later, 25 to 30 hours after nest is placed in contact with the marked humus.There was no significant difference in the distribution of P³² according to the zone from which samples of the population were taken, exept in the case of the soldiers from nests set apart for a short time in the humus.Workers are very rapidly contaminated, and the distribution of phosphorus in this cast is heterogenous. Certain workers did not feed directly on the humus during the period of the experiment; they received, along whith the soldiers, regurgitated food (stomodeal). The queens is the first to be contaminated by salivary liquid from workers, and her radioactivity indicates a constant absorption of nourishment. The alates, close to nuptial flight, as well as white soldiers are heavily loaded with saliva. The hatch, nymphs of the last but one stage and the king, receive only a poor quantity of saliva. The king has few needs and a slow rate of feeding. The nymphs indoubtedly resort to another mode of feeding during the penultimate stage.These data will be completed by a specialized study of the different casts.

     

A new assay capturing chromosome fusions shows a protection trade-off at telomeres and NHEJ vulnerability to low-density ionizing radiation

Chromosome fusions threaten genome integrity and promote cancer by engaging catastrophic mutational processes, namely chromosome breakage–fusion–bridge cycles and chromothripsis. Chromosome fusions are frequent in cells incurring telomere dysfunctions or those exposed to DNA breakage. Their occurrence and therefore their contribution to genome instability in unchallenged cells is unknown. To address this issue, we constructed a genetic assay able to capture and quantify rare chromosome fusions in budding yeast. This chromosome fusion capture (CFC) assay relies on the controlled inactivation of one centromere to rescue unstable dicentric chromosome fusions. It is sensitive enough to quantify the basal rate of end-to-end chromosome fusions occurring in wild-type cells. These fusions depend on canonical nonhomologous end joining (NHEJ). Our results show that chromosome end protection results from a trade-off at telomeres between positive effectors (Rif2, Sir4, telomerase) and a negative effector partially antagonizing them (Rif1). The CFC assay also captures NHEJ-dependent chromosome fusions induced by ionizing radiation. It provides evidence for chromosomal rearrangements stemming from a single photon–matter interaction.     

Modularity as a source of new morphological variation in the mandible of hybrid mice

ABSTRACT: BACKGROUND: Hybridization is often seen as a process dampening phenotypic differences accumulated between diverging evolutionary units. For a complex trait comprising several relatively independent modules, hybridization may however simply generate new phenotypes, by combining into a new mosaic modules inherited from each parental groups and parts intermediate with respect to the parental groups. We tested this hypothesis by studying mandible size and shape in a set of first and second generation hybrids resulting from inbred wild-derived laboratory strains documenting two subspecies of house mice, Musmusculusdomesticus and Musmusculusmusculus. Phenotypic variation of the mandible was divided into nested partitions of developmental, evolutionary and functional modules. RESULTS: The size and shape of the modules were differently influenced by hybridization. Some modules seemed to be the result of typical additive effects with hybrids intermediate between parents, some displayed a pattern expected in the case of monogenic dominance, whereas in other modules, hybrids were transgressive. The result is interpreted as the production of novel mandible morphologies. Beyond this modularity, modules in functional interaction tended to display significant covariations. CONCLUSIONS: Modularity emerges as a source of novel morphological variation by its simple potential to combine different parts of the parental phenotypes into a novel offspring mosaic of modules. This effect is partly counterbalanced by bone remodeling insuring an integration of the mosaic mandible into a functional ensemble, adding a non-genetic component to the production of transgressive phenotypes in hybrids.     

Examining water temperature proxies in<Emphasis Type="Italic"> Porites</Emphasis> corals from the Great Barrier Reef: a cross-shelf comparison

Cores from colonies of the coral species Porites sp. were collected from inshore, mid-shelf, and outer reef localities (central Great Barrier Reef) to test the robustness of the major elemental sea surface temperature (SST) proxies (B/Ca, Mg/Ca, Sr/Ca, U/Ca) to the influence of inshore processes. Time series analyses of Sr/Ca, U/Ca, B/Ca, and Mg/Ca are compared to sea surface temperature (SST) in order to provide calibrations for these elements. This study shows that there are significant variations between the corals with respect to some of the proxies. In some cases, variations of ~6 °C are observed for a single U/Ca value. This magnitude of variation is also seen in the Mg/Ca proxy and, to a smaller extent, in the B/Ca–SST relationship. In two of the corals, both Mg/Ca and U/Ca do not follow a seasonal signal. The Mg/Ca and U/Ca ratios for two inshore corals are significantly different than the offshore corals (lower and higher, respectively). The other two proxies (B/Ca and Sr/Ca) do not display any inshore vs. offshore variations except for one inshore site that did not have a clear seasonal signal for either of these proxies. The Sr/Ca–SST relationship is the most robust, with a temperature variation of ~2 °C for a single Sr/Ca value, which is within error for this technique.     

Distinct sites on ABCA1 control distinct steps required for cellular release of phospholipids

The loss of ABCA1 function leads to Tangier dyslipidemia in humans and to a Tangier-like phenotype in mice, by impairing the transformation of nascent apolipoproteins into mature HDL particles. Mechanistically this ensues from the inability of cells to release membrane lipids and cholesterol. Whereas the ability of ABCA1 to promote phospholipid effluxes, surface binding of apolipoproteins and outward flip of membrane lipids has been documented, the relationship between this series of ABCA1-dependent events is still elusive. Here we provide evidence that i) lipid effluxes require both flip of membrane lipids and binding of apolipoproteins to the cell surface, ii) apolipoprotein A-I binding depends on structural determinants on ABCA1, and iii) phospholipid effluxes can be modulated by engineered mutations on the structural determinants identified on ABCA1.