Lipid composition of blood platelets and erythrocytes of southern elephant seal (Mirounga leonina) and antarctic fur seal (Arctocephalus gazella)

Erythrocyte and blood platelet phospholipid compositions were studied in three elephant seals and two fur seals, two species of marine mammals living in the Subantarctic region feeding on preys rich in (n-3) polyunsaturated fatty acids. Results were compared with those reported for related species and humans. In erythrocytes, the phospholipid (PL) and cholesterol (CHOL) contents were lower in pinnipeds than in humans. Phosphatidylcholine (PC) levels were higher in elephant seals than in fur seals, with a reverse trend for phosphatidylethanolamine (PE) and phosphatidylserine (PS). Both species had lower SM/PC ratios and PE plasmalogen concentrations than human. Erythrocytes were richer in (n-3) fatty acids (FA) in pinnipeds than in humans. In platelets, the PL content was lower and the CHOL content higher in elephant seals than in humans or in other phocid seal species studied to date. The SM/PC ratio was much higher than in other seal species or in man. In both species, the proportion of PE plasmalogens was higher in platelets than in erythrocytes. PL were more saturated in elephant seals than in fur seals. These results suggest that the erythrocytes and platelets of wild marine mammals may prove useful models to study the influence of dietary lipids on the structure and hemostatic function of these cells.     

Soil depth detection by seeds and diurnally fluctuating temperatures: different dynamics in 10 annual plants

Background and Aims

Seeds buried in the soil detect burial depth through light and diurnally fluctuating temperatures (DFT) and in this way limit losses due to germination too deep in the soil. DFTs and germination also increase in vegetation gaps. However, dry open environments with high DFTs can also increase seedling mortality, creating conflicting selection pressures for reaction to DFTs. Since this questions the general function of DFT detection, we therefore tested if interspecific differences in DFT detection are related to mortality in different soil depths.

Methods

We buried seeds of ten annual plants including species pairs of increasing and decreasing germination in response to DFTs. Seeds were buried in 5, 10 and 25cm soil depth and exhumed after two different burial times. Seed viability was tested using germination in growth chambers and tetrazolium. We also measured DFTs at these depths using temperature data loggers.

Results

DFT detection was not related to differences in mortality at three burial depths. Three species showed a clear pattern of depth dependent mortality, however inconsistently related to DFT detection.

Conclusions

Depth detection mechanisms are more species-specific than expected. Hence, interspecific differences in seed mortalities are difficult to predict by DFT detection alone and alternative soil depth sensing mechanisms should be explored in future.     

P2 receptors and platelet function

Following vessel wall injury, platelets adhere to the exposed subendothelium, become activated and release mediators such as TXA₂ and nucleotides stored at very high concentration in the so-called dense granules. Released nucleotides and other soluble agents act in a positive feedback mechanism to cause further platelet activation and amplify platelet responses induced by agents such as thrombin or collagen. Adenine nucleotides act on platelets through three distinct P2 receptors: two are G protein-coupled ADP receptors, namely the P2Y₁ and P2Y₁₂ receptor subtypes, while the P2X₁ receptor ligand-gated cation channel is activated by ATP. The P2Y₁ receptor initiates platelet aggregation but is not sufficient for a full platelet aggregation in response to ADP, while the P2Y₁₂ receptor is responsible for completion of the aggregation to ADP. The latter receptor, the molecular target of the antithrombotic drugs clopidogrel, prasugrel and ticagrelor, is responsible for most of the potentiating effects of ADP when platelets are stimulated by agents such as thrombin, collagen or immune complexes. The P2X₁ receptor is involved in platelet shape change and in activation by collagen under shear conditions. Each of these receptors is coupled to specific signal transduction pathways in response to ADP or ATP and is differentially involved in all the sequential events involved in platelet function and haemostasis. As such, they represent potential targets for antithrombotic drugs.     

Lost your orientation? Find your way with PtdIns(3,4,5)P3!

Faithful chromosome segregation requires correct positioning of the spindle during mitosis. In this issue of Developmental Cell, Toyoshima et al. describe a new mechanism for spindle orientation involving phosphatidylinositol-3,4,5-triphosphate [PtdIns(3,4,5)P3]. They found that in metaphase cells, dynactin was associated with the cortex through the actin cytoskeleton, and accumulated in the midsections in a PtdIns(3,4,5)P3-dependent manner. Thus, PtdIns(3,4,5)P3 regulates spindle orientation through dynein-dynactin motor complexes.     

A probabilistic approach to the use of pollen indicators for plant attributes and biomes: an application to European vegetation at 0 and 6 ka

Aim This paper presents a probabilistic method for the characterization of pollen taxa using attributes, and for the reconstitution of past biomes. The probabilities are calculated on the basis of European floristic and pollen databases sufficiently large and exhaustive to provide robust estimates. Location The analysis is based on data from approximately 1000 sites throughout Europe. Method We use all the pollen data from the European Pollen Database (EPD), which contains about 50 000 pollen assemblages distributed across Europe and covering the period from the Last Glacial Maximum to the present. Using existing floras, each pollen taxon has been characterized by allocating one or more modes of several attributes, chosen according to the biogeography and phenology of the taxon. With this information, conditional probabilities are defined, representing the chance of a given attribute mode occurring in a given pollen spectrum, when the taxa assemblage is known. The concept of co‐occurrence is used to provide a greater amount of information to compensate for difficulties in the identification of pollen grains, allowing a better interpretation when there is little diversity in the pollen assemblage. Results The method has been validated using a dataset of modern samples against existing methods of biome classification and remote sensing data. An application is proposed in which the new method is used to produce biomes for pollen data 6000 years ago. This confirms previous results showing an extension of the deciduous forest to the north, east and south, explained by milder winters in western and northern Europe, and cooler and wetter climate in the Mediterranean region. Conclusion The results show the new method to be efficient, reliable and flexible and to be an improvement over the previous method of biomization. They will be used to test simulations of earth system models running on periods with climate significantly different from the present day, enabling a robust test of the validity of applying these models to the future.     

Direct voltage control of signaling via P2Y1 and other Galphaq-coupled receptors

Emerging evidence suggests that Ca2+ release evoked by certain G-protein-coupled receptors can be voltage-dependent; however, the relative contribution of different components of the signaling cascade to this response remains unclear. Using the electrically inexcitable megakaryocyte as a model system, we demonstrate that inositol 1,4,5-trisphosphate-dependent Ca2+ mobilization stimulated by several agonists acting via Galphaq-coupled receptors is potentiated by depolarization and that this effect is most pronounced for ADP. Voltage-dependent Ca2+ release was not induced by direct elevation of inositol 1,4,5-trisphosphate, by agents mimicking diacylglycerol actions, or by activation of phospholipase Cgamma-coupled receptors. The response to voltage did not require voltage-gated Ca2+ channels as it persisted in the presence of nifedipine and was only weakly affected by the holding potential. Strong predepolarizations failed to affect the voltage-dependent Ca2+ increase; thus, an alteration of G-protein betagamma subunit binding is also not involved. Megakaryocytes from P2Y1(-/-) mice lacked voltage-dependent Ca2+ release during the application of ADP but retained this response after stimulation of other Galphaq-coupled receptors. Although depolarization enhanced Ca2+ mobilization resulting from GTPgammaS dialysis and to a lesser extent during AlF4- or thimerosal, these effects all required the presence of P2Y1 receptors. Taken together, the voltage dependence to Ca2+ release via Galphaq-coupled receptors is not due to control of G-proteins or down-stream signals but, rather, can be explained by a voltage sensitivity at the level of the receptor itself. This effect, which is particularly robust for P2Y1 receptors, has wide-spread implications for cell signaling.     

Mechanism controlling perpendicular alignment of the spindle to the axis of cell division in fission yeast

In animal cells, the mitotic spindle is aligned perpendicular to the axis of cell division. This ensures that sister chromatids are separated to opposite sides of the cytokinetic actomyosin ring (CAR). We show that, in fission yeast, spindle rotation is dependent on the interaction of astral microtubules with the cortical actin cytoskeleton. Interaction initially occurs with a region surrounding the nucleus, which we term the astral microtubule interaction zone (AMIZ). Simultaneous contact of astral microtubules from both poles with the AMIZ directs spindle rotation and this requires both actin and two type V myosins, Myo51 and Myo52. Astral microtubules from one pole only then contact the CAR, which is located at the centre of the AMIZ. We demonstrate that the anillin homologue Mid1, which dictates correct placement of the CAR, is necessary to stabilise the mitotic spindle perpendicular to the axis of cell division. Finally, we show that the position of the mitotic spindle is monitored by a checkpoint that regulates the timing of sister chromatid separation.