Cell volume and the regulation of apoptotic cell death

Apoptosis is a physiological mechanism allowing for the removal of abundant or potentially harmful cells. The hallmarks of apoptosis include degradation of cellular DNA, exposure of phosphatidylserine at the outer leaflet of the cell membrane and cell shrinkage. Phosphatidylserine exposure favours adhesion to macrophages with subsequent phagocytosis of the shrunken apoptotic particles. The interaction of cell volume regulatory mechanisms and apoptosis is illustrated in two different model systems, i.e. (a) lymphocyte apoptosis following stimulation of CD95 receptor and (b) erythrocyte apoptosis upon cell shrinkage. (a) Triggering of CD95 in Jurkat T lymphocytes is paralleled by activation of cell volume regulatory Cl- channels, inhibition of the Na+/H+ exchanger and osmolyte release. The latter coincides with cell shrinkage, DNA fragmentation and phosphatidylserine exposure. CD95 stimulation leads to early inhibition of the voltage gated K+ channel Kv1.3, which may contribute to the inhibition of the Ca2+ release activated Ca2+ channel I(CRAC). (b) Osmotic shock of erythrocytes activates a cell volume regulatory cation conductance allowing the entry not only of Na+ but of Ca2+ as well. Increased cytosolic Ca2+ stimulates a scramblase which disrupts the phosphatidylserine asymmetry of the cell membrane, leading to phosphatidylserine exposure. The cation conductance is further activated by oxidative stress and energy depletion and inhibited by Cl-. Shrinkage of erythrocytes stimulates in addition a sphingomyelinase with subsequent formation of ceramide which potentiates the effect of cytosolic Ca2+ on phosphatidylserine. In conclusion, cell volume-sensitive mechanisms participate in the triggering of apoptosis following receptor stimulation or cell injury.     

Anthropology takes control of morphometrics

There has been a startling change over the last decade in the intellectual context of morphometrics. In the 1990's, this field, which has not altered its focus upon the quantitative analysis of biomedical shape variation and shape change, was principally centered around concerns of medical image analysis; but now it is driven mainly by the demands of researchers in human variability, physical anthropology, primatology, and paleoanthropology instead. This essay celebrates that change and tries to account for it by reference to cognitive and intellectual aspects of the new home.     

Use of the fluorescent timer DsRED-E5 as reporter to monitor dynamics of gene activity in plants

Fluorescent proteins, such as green fluorescent protein and red fluorescent protein (DsRED), have become frequently used reporters in plant biology. However, their potential to monitor dynamic gene regulation is limited by their high stability. The recently made DsRED-E5 variant overcame this problem. DsRED-E5 changes its emission spectrum over time from green to red in a concentration independent manner. Therefore, the green to red fluorescence ratio indicates the age of the protein and can be used as a fluorescent timer to monitor dynamics of gene expression. Here, we analyzed the potential of DsRED-E5 as reporter in plant cells. We showed that in cowpea (Vigna unguiculata) mesophyll protoplasts, DsRED-E5 changes its fluorescence in a way similar to animal cells. Moreover, the timing of this shift is suitable to study developmental processes in plants. To test whether DsRed-E5 can be used to monitor gene regulation in plant organs, we placed DsRED-E5 under the control of promoters that are either up- or down-regulated (MtACT4 and LeEXT1 promoters) or constitutively expressed (MtACT2 promoter) during root hair development in Medicago truncatula. Analysis of the fluorescence ratios clearly provided more accurate insight into the timing of promoter activity.     

Repair of potentially lethal damage does not depend on functional TP53 in human glioblastoma cells

The functionality of G(1)-phase arrest was investigated in relation to repair of potentially lethal damage (PLD) in human glioblastoma Gli-06 cells. Confluent cultures were irradiated and plated for clonogenic survival either immediately or 24 h after gamma irradiation. Bivariate flow cytometry was performed to assess the distribution over the cell cycle. Levels of TP53 and CDKN1A protein were assessed with Western blotting and levels of CDKN1A mRNA with RT-PCR. Confluence significantly reduced the number of proliferating cells. Marked PLD repair was found in the absence of an intact G(1) arrest. No accumulation of TP53 was observed, and the protein was smaller than the wild-type TP53 of RKO cells. No increased expression of CDKN1A at the mRNA or protein levels was found in Gli-06 cells. The TP53 of Gli-06 cells was unable to transactivate the CDKN1A gene. From this study, it is evident that PLD repair may be present without a functional TP53 or G(1) arrest.     

Heat shock protein-mediated resistance to high hydrostatic pressure in Escherichia coli

A random library of Escherichia coli MG1655 genomic fragments fused to a promoterless green fluorescent protein (GFP) gene was constructed and screened by differential fluorescence induction for promoters that are induced after exposure to a sublethal high hydrostatic pressure stress. This screening yielded three promoters of genes belonging to the heat shock regulon (dnaK, lon, clpPX), suggesting a role for heat shock proteins in protection against, and/or repair of, damage caused by high pressure. Several further observations provide additional support for this hypothesis: (i). the expression of rpoH, encoding the heat shock-specific sigma factor sigma(32), was also induced by high pressure; (ii). heat shock rendered E. coli significantly more resistant to subsequent high-pressure inactivation, and this heat shock-induced pressure resistance followed the same time course as the induction of heat shock genes; (iii). basal expression levels of GFP from heat shock promoters, and expression of several heat shock proteins as determined by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins extracted from pulse-labeled cells, was increased in three previously isolated pressure-resistant mutants of E. coli compared to wild-type levels.     

Conservation of protein-protein interactions - lessons from ascomycota

Interacting proteins from Saccharomyces cerevisiae are evolutionarily conserved and their likelihood of having an ortholog in other ascomycota species correlates with the number of interaction partners. Moreover, interacting proteins show a clear preference to be conserved as a pair, indicating that nature maintains selection pressure on the interaction links between proteins. The conservation of interacting protein pairs between different organisms does not exhibit any bias with respect to protein functional roles.     

Interannual Variation in Timing of Parturition and Growth of Collared Pikas (Ochotona collaris) in the Southwest Yukon

The length of the snow-free season has a significant influenceon reproduction and growth in northern alpine environments,and these life history traits may provide sensitive indicatorsof the responses of organisms to climate change. We examinedgrowth rates and timing of parturition of collared pikas (Ochotonacollaris) from 1995–2002 in the Ruby Range, Yukon Territory,Canada. Growth rates were best described using a Gompertz model,in which the asymptotic mass, determined from the average maleand female weights, was 157 g, the growth rate constant (K)was 0.0557, and the age at inflection (I) was 18.12 days, fora birth weight of 10 g. The maximum growth rate for North Americanpikas (O. collaris and O. princeps) increased with latitude,with maximum growth rates being approximately one-third greaterin northern populations where the snow-free season is less thanthree months long. The mean parturition date varied significantlyamong years from 3 June to 3 July, and delayed parturition wascorrelated with indices of high snow accumulation and, to alesser extent, late spring snowmelt. However, parturition datedid not significantly affect the subsequent over-winter survivalof juveniles in this population, suggesting that pikas are ableto adjust to seasonal uncertainty associated with highly variablespring conditions.     

Effect of Vibrio parahaemolyticus haemolysin on human erythrocytes

Haemolysin Kanagawa, a toxin from Vibrio parahaemolyticus, is known to trigger haemolysis. Flux studies indicated that haemolysin forms a cation channel. In the present study, channel properties were elucidated by patch clamp and functional significance of ion fluxes by fluorescence-activated cell sorting (FACS) analysis. Treatment of human erythrocytes with 1 U ml-1 haemolysin within minutes induces a non-selective cation permeability. Moreover, haemolysin activates clotrimazole-sensitive K+ channels, pointing to stimulation of Ca2+-sensitive Gardos channels. Haemolysin (1 U ml-1) leads within 5 min to slight cell shrinkage, which is reversed in Ca2+-free saline. Erythrocytes treated with haemolysin (0.1 U ml-1) do not undergo significant haemolysis within the first 60 min. Replacement of extracellular Na+ with NMDG+ leads to slight cell shrinkage, which is potentiated by 0.1 U ml-1 haemolysin. According to annexin binding, treatment of erythrocytes with 0.1 U ml-1 haemolysin leads within 30 min to breakdown of phosphatidylserine asymmetry of the cell membrane, a typical feature of erythrocyte apoptosis. The annexin binding is significantly blunted at increased extracellular K+ concentrations and by K+ channel blocker clotrimazole. In conclusion, haemolysin Kanagawa induces cation permeability and activates endogenous Gardos K+ channels. Consequences include breakdown of phosphatidylserine asymmetry, which depends at least partially on cellular loss of K+.     

How does parkin ligate ubiquitin to Parkinson's disease?

Recessive mutations in the human PARKIN gene are the most common cause of hereditary parkinsonism, which arises from the degeneration of dopaminergic neurons in the substantia nigra. However, the molecular mechanisms by which the loss of parkin causes dopaminergic neurodegeneration are not well understood. Parkin is an enzyme that ubiquitinates several candidate substrate proteins and thereby targets them for proteasomal degradation. Hypothesis-driven searches have led to the discovery of aggregation-prone protein substrates of parkin. Moreover, the enzyme is upregulated when under unfolded protein stress. Thus, loss-of-function mutations of parkin might impair the removal of potentially toxic protein aggregates. However, the limited neuropathological information that is available from parkin-proven patients, as well as the recent knockout of the parkin gene in fruit flies and mice, may indicate a more complex disease mechanism, possibly involving the misfolding of parkin itself or of additional substrates. The risk factors that predispose dopaminergic neurons to degenerate on parkin failure are yet to be identified.