A positive relationship between functional redundancy and temperature in Cenozoic marine ecosystems

The long-term effects of climate change on biodiversity and biogeographic patterns are uncertain. There are known relationships between geographic area and both the number of species and the number of ecological functional groups-termed the species-area relationship and the functional diversity-area relationship, respectively. We show that there is a positive relationship between the number of species in an area, the number of ecological functional groups, and oceanic temperature in the shallow-marine fossil record of New Zealand over a time span of ~40 million years. One implication of this relationship is that functional redundancy increases with temperature. This reveals a long-lived and persistent association between the spatial structuring of biodiversity, the temperature-dependence of functional redundancy, and shallow-marine biodiversity in mid-latitudes.

Evaluation of two commercial, rapid, ELISA kits testing for scrapie in retro-pharyngeal lymph nodes in sheep

AIMS

To estimate the number of cases of scrapie that would occur in sheep of different prion protein (PrP) genotypes if scrapie was to become established in New Zealand, and to compare the performance of two commercially available, rapid ELISA kits using ovine retro-pharyngeal lymph nodes (RLN) from non-infected and infected sheep of different PrP genotypes.

METHODS

Using published data on the distribution of PrP genotypes within the New Zealand sheep flock and the prevalence of cases of scrapie in these genotypes in the United Kingdom, the annual expected number of cases of scrapie per genotype was estimated, should scrapie become established in New Zealand, assuming a total population of 28 million sheep. A non-infected panel of RLN was collected from 737 sheep from New Zealand that had been culled, found in extremis or died. Brain stem samples were also collected from 131 of these sheep. A second panel of infected samples comprised 218 and 117 RLN from confirmed scrapie cases that had originated in Europe and the United States of America, respectively. All samples were screened using two commercial, rapid, transmissible spongiform encephalopathy ELISA kits: Bio-Rad TeSeE ELISA (ELISA-BR), and IDEXX HerdChek BSE-Scrapie AG Test (ELISA-ID).

RESULTS

If scrapie became established in New Zealand, an estimated 596 cases would occur per year; of these 234 (39%) and 271 (46%) would be in sheep carrying ARQ/ARQ and ARQ/VRQ PrP genotypes, respectively. For the non-infected samples from New Zealand the diagnostic specificity of both ELISA kits was 100%. When considering all infected samples, the diagnostic sensitivity was 70.4 (95% CI=65.3-75.3)% for ELISA-BR and 91.6 (95% CI=88.2-94.4)% for ELISA-ID. For the ARQ/ARQ genotype (n=195), sensitivity was 66.2% for ELISA-BR and 90.8% for ELISA-ID, and for the ARQ/VRQ genotype (n=107), sensitivity was 81.3% for ELISA-BR and 98.1% for ELISA-ID.

CONCLUSIONS

In this study, the ELISA-ID kit demonstrated a higher diagnostic sensitivity for detecting scrapie in samples of RLN from sheep carrying scrapie-susceptible PrP genotypes than the ELISA-BR kit at comparable diagnostic specificity.

CLINICAL RELEVANCE

The diagnostic performance of the ELISA-ID kit using ovine RLN merits the consideration of including this assay in the national scrapie surveillance programme in New Zealand.

Rate, extent and concentration dependence of histamine-evoked Weibel-Palade body exocytosis determined from individual fusion events in human endothelial cells

The rate, concentration dependence and extent of histamine-evoked Weibel-Palade body (WPB) exocytosis were investigated with time-resolved fluorescence microscopy in cultured human umbilical vein endothelial cells expressing WPB-targeted chimeras of enhanced green fluorescent protein (EGFP). Exocytosis of single WPBs was characterized by an increase in EGFP fluorescence, morphological changes and release of WPB contents. The fluorescence increase was due to a rise of intra-WPB pH from resting levels, estimated as pH 5.45+/-0.26 (s.d., n=144), to pH 7.40. It coincided with uptake of extracellular Alexa-647, indicating the formation of a fusion pore, prior to loss of fluorescent contents. Delays between the increase in intracellular free calcium ion concentration evoked by histamine and the first fusion event were 10.0+/-4.42 s (n=9 cells) at 0.3 microM histamine and 1.57+/-0.21 s (n=15 cells) at 100 microM histamine, indicating the existence of a slow process or processes in histamine-evoked WPB exocytosis. The maximum rates of exocytosis were 1.20+/-0.16 WPB s(-1) (n=9) at 0.3 microM and 3.66+/-0.45 WPB s(-1) at 100 microM histamine (n=15). These occurred 2-5 s after histamine addition and declined to lower rates with continued stimulation. The initial delays and maximal rate of exocytosis were unaffected by removal of external Ca2+ indicating that the initial burst of secretion is driven by Ca2+ release from internal stores, but sustained exocytosis required external Ca2+. Data were compared to exocytosis evoked by a maximal concentration of the strong secretagogue ionomycin (1 microM), for which there was a delay between calcium elevation and secretion of 1.67+/-0.24 s (n=6), and a peak fusion rate of approximately 10 WPB s(-1).

Orbitally induced oscillations in the East Antarctic ice sheet at the Oligocene/Miocene boundary

Between 34 and 15 million years (Myr) ago, when planetary temperatures were 3-4 degrees C warmer than at present and atmospheric CO2 concentrations were twice as high as today, the Antarctic ice sheets may have been unstable. Oxygen isotope records from deep-sea sediment cores suggest that during this time fluctuations in global temperatures and high-latitude continental ice volumes were influenced by orbital cycles. But it has hitherto not been possible to calibrate the inferred changes in ice volume with direct evidence for oscillations of the Antarctic ice sheets. Here we present sediment data from shallow marine cores in the western Ross Sea that exhibit well dated cyclic variations, and which link the extent of the East Antarctic ice sheet directly to orbital cycles during the Oligocene/Miocene transition (24.1-23.7 Myr ago). Three rapidly deposited glacimarine sequences are constrained to a period of less than 450 kyr by our age model, suggesting that orbital influences at the frequencies of obliquity (40 kyr) and eccentricity (125 kyr) controlled the oscillations of the ice margin at that time. An erosional hiatus covering 250 kyr provides direct evidence for a major episode of global cooling and ice-sheet expansion about 23.7 Myr ago, which had previously been inferred from oxygen isotope data (Mi1 event).

Cholesterol binds to synaptophysin and is required for biogenesis of synaptic vesicles

Here, to study lipid-protein interactions that contribute to the biogenesis of regulated secretory vesicles, we have developed new approaches by which to label proteins in vivo, using photoactivatable cholesterol and glycerophospholipids. We identify synaptophysin as a major specifically cholesterol-binding protein in PC12 cells and brain synaptic vesicles. Limited cholesterol depletion, which has little effect on total endocytic activity, blocks the biogenesis of synaptic-like microvesicles (SLMVs) from the plasma membrane. We propose that specific interactions between cholesterol and SLMV membrane proteins, such as synaptophysin, contribute to both the segregation of SLMV membrane constituents from plasma-membrane constituents, and the induction of synaptic-vesicle curvature.

Synaptic vesicle biogenesis

Synaptic vesicles, which have been a paradigm for the fusion of a vesicle with its target membrane, also serve as a model for understanding the formation of a vesicle from its donor membrane. Synaptic vesicles, which are formed and recycled at the periphery of the neuron, contain a highly restricted set of neuronal proteins. Insight into the trafficking of synaptic vesicle proteins has come from studying not only neurons but also neuroendocrine cells, which form synaptic-like microvesicles (SLMVs). Formation and recycling of synaptic vesicles/SLMVs takes place from the early endosome and the plasma membrane. The cytoplasmic machinery of synaptic vesicle/SLMV formation and recycling has been studied by a variety of experimental approaches, in particular using cell-free systems. This has revealed distinct machineries for membrane budding and fission. Budding is mediated by clathrin and clathrin adaptors, whereas fission is mediated by dynamin and its interacting protein SH3p4, a lysophosphatidic acid acyl transferase.

Selective localization of the polytopic membrane protein prominin in microvilli of epithelial cells - a combination of apical sorting and retention in plasma membrane protrusions

Prominin is a recently identified polytopic membrane protein expressed in various epithelial cells, where it is selectively associated with microvilli. When expressed in non-epithelial cells, prominin is enriched in plasma membrane protrusions. This raises the question of whether the selective association of prominin with microvilli in epithelial cells is solely due to its preference for, and stabilization in, plasma membrane protrusions, or is due to both sorting to the apical plasma membrane domain and subsequent enrichment in plasma membrane protrusions. To investigate this question, we have generated stably transfected MDCK cells expressing either full-length or C-terminally truncated forms of mouse prominin. Confocal immunofluorescence and domain-selective cell surface biotinylation experiments on transfected MDCK cells grown on permeable supports demonstrated the virtually exclusive apical localization of prominin at steady state. Pulse-chase experiments in combination with domain-selective cell surface biotinylation showed that newly synthesized prominin was directly targeted to the apical plasma membrane domain. Immunoelectron microscopy revealed that prominin was confined to microvilli rather than the planar region of the apical plasma membrane. Truncation of the cytoplasmic C-terminal tail of prominin impaired neither its apical cell surface expression nor its selective retention in microvilli. Both the apical-specific localization of prominin and its selective retention in microvilli were maintained when MDCK cells were cultured in low-calcium medium, i.e. in the absence of tight junctions. Taken together, our results show that: (i) prominin contains dual targeting information, for direct delivery to the apical plasma membrane domain and for the enrichment in the microvillar subdomain; and (ii) this dual targeting does not require the cytoplasmic C-terminal tail of prominin and still occurs in the absence of tight junctions. The latter observation suggests that entry into, and retention in, plasma membrane protrusions may play an important role in the establishment and maintenance of the apical-basal polarity of epithelial cells.

p24 and p23, the major transmembrane proteins of COPI-coated transport vesicles, form hetero-oligomeric complexes and cycle between the organelles of the early secretory pathway

COPI-coated vesicles that bud off the Golgi complex contain two major transmembrane proteins, p23 and p24. We have localized the protein at the Golgi complex and at COPI-coated vesicles. Transport from the intermediate compartment (IC) to the Golgi can be blocked at 15 degrees C, and under these conditions p24 accumulates in peripheral punctated structures identified as IC. Release from the temperature block leads to a redistribution of p24 to the Golgi, showing that p24, similar to p23, cycles between the IC and Golgi complex. Immunoprecipitations of p24 from cell lysates and from detergent-solubilized Golgi membranes and COPI-coated vesicles show that p24 and p23 interact with each other to form a complex. Transient transfection of p23 in HeLa cells shows that p23 and p24 colocalize in structures induced by the overexpression of p23. Taken together p24 interacts with p23 and constitutively cycles between the organelles of the early secretory pathway.

Differential extraction of proteins from paraformaldehyde-fixed cells: lessons from synaptophysin and other membrane proteins

While investigating the localization of synaptophysin in PC12 cells using immunofluorescence microscopy, we noticed a striking difference in its apparent subcellular distribution depending on whether digitonin or Triton X-100 was used as permeabilization agent of paraformaldehyde (PFA)-fixed cells. We found that this difference was due to epitope inaccessibility in the digitonin-treated cells combined with an almost quantitative extraction of the antigen on Triton X-100 permeabilization. Both phenomena were differential with respect to the various synaptophysin-containing compartments. The extraction of antigen from PFA-fixed cells was also seen with other membrane proteins but not with cytosolic proteins and proteins in the lumen of the secretory pathway. Significantly, some of the membrane proteins were extracted from the PFA-fixed cells in higher-molecular-weight forms which we believe represent their in vivo oligomeric states. The implications of our observations are discussed with respect to the method of immunofluorescence microscopy and also to the possible use of paraformaldehyde as an in vivo crosslinker for the study of membrane protein quaternary structure.

Synaptic-like microvesicles of neuroendocrine cells originate from a novel compartment that is continuous with the plasma membrane and devoid of transferrin receptor

We have characterized the compartment from which synaptic-like microvesicles (SLMVs), the neuroendocrine counterpart of neuronal synaptic vesicles, originate. For this purpose we have exploited the previous observation that newly synthesized synaptophysin, a membrane marker of synaptic vesicles and SLMVs, is delivered to the latter organelles via the plasma membrane and an internal compartment. Specifically, synaptophysin was labeled by cell surface biotinylation of unstimulated PC12 cells at 18 degrees C, a condition which blocked the appearance of biotinylated synaptophysin in SLMVs and in which there appeared to be no significant exocytosis of SLMVs. The majority of synaptophysin labeled at 18 degrees C with the membrane-impermeant, cleavable sulfo-NHS-SS-biotin was still accessible to extracellularly added MesNa, a 150-D membrane-impermeant thiol-reducing agent, but not to the 68,000-D protein avidin. The SLMVs generated upon reversal of the temperature to 37 degrees C originated exclusively from the membranes containing the MesNa-accessible rather than the MesNa-protected population of synaptophysin molecules. Biogenesis of SLMVs from MesNa-accessible membranes was also observed after a short (2 min) biotinylation of synaptophysin at 37 degrees C followed by chase. In contrast to synaptophysin, transferrin receptor biotinylated at 18 degrees or 37 degrees C became rapidly inaccessible to MesNa. Immunofluorescence and immunogold electron microscopy of PC12 cells revealed, in addition to the previously described perinuclear endosome in which synaptophysin and transferrin receptor are colocalized, a sub-plasmalemmal tubulocisternal membrane system distinct from caveolin-positive caveolae that contained synaptophysin but little, if any, transferrin receptor. The latter synaptophysin was selectively visualized upon digitonin permeabilization and quantitatively extracted, despite paraformaldehyde fixation, by Triton X-100. Synaptophysin biotinylated at 18 degrees C was present in these subplasmalemmal membranes. We conclude that SLMVs originate from a novel compartment that is connected to the plasma membrane via a narrow membrane continuity and lacks transferrin receptor.

Thymosin peptides stimulate corticotropin release by a calcium-dependent mechanism

Thymosin fraction five (TF5), a well-characterized immunoregulatory thymic preparation, has been reported to stimulate corticotropin (ACTH) release from rat pituitary cells. Since a previous study in our laboratory had shown that TF5 was able to stimulate ACTH release from corticotropin-releasing hormone (CRH)-insensitive corticotropic tumor cells, it was of interest to assess the role of calcium in the mechanism of action of TF5 on corticotropic cells. A CRH-insensitive variant, denoted AtT-20(CI), of the wild-type corticotropic tumor cell line AtT-20 was used. Synthetic h/rCRH within a dose range of 0.1-100 nM was completely ineffective to stimulate basal ACTH release from AtT-20(CI) cells, although the same batch of neuropeptide displayed the expected ACTH-releasing activity on dispersed rat pituitary cells (for instance, 0.1 nM CRH induced a 3.7-fold increase in ACTH release in this cell system). Median eminence extracts (1/10) induced only a 12% increase in ACTH release from AtT-20(CI) cells as compared to the 395% stimulation induced in normal pituitary cells. As expected, TF5 induced a dose-dependent increase in ACTH release from AtT-20(CI) cells. However, this ACTH-releasing activity of TF5 was completely abolished when cells were incubated in Ca-free medium or Ca-free medium containing 0.5 mM EGTA. On the other hand, the presence of the Ca ionophore A23187 (5 microM) in medium containing normal Ca levels (2.5 mM) did not affect the ACTH-releasing activity of TF5 on AtT-20(CI) cells.(ABSTRACT TRUNCATED AT 250 WORDS)