A Caenorhabditis elegans wee1 homolog is expressed in a temporally and spatially restricted pattern during embryonic development

A wee1 homolog, wee-1.1, is expressed in both a temporally and spatially restricted pattern during early Caenorhabditis elegans embryogenesis, and is undetectable throughout the remainder of embryogenesis. The wee-1.1 message appears to be zygotically expressed in the somatic founder cell E of the 12-cell embryo. This expression disappears when the E blastomere divides for the first time. The wee-1.1 message then appears transiently in the nuclei of the eight great-granddaughter cells of the AB somatic founder cell, just before these cells divide in the 16-cell embryo. Following this division, the wee-1.1 mRNA is no longer detectable throughout the remainder of embryogenesis. The expression of wee-1.1 in the E blastomere and in the AB progeny appears to be restricted to nuclei in prophase and metaphase of the cell cycle. Analysis of the wee-1.1 mRNA expression pattern in maternal-effect lethal mutants suggests that this expression pattern is restricted to cells of the E and AB fates in the early embryo. This mRNA expression pattern is restricted to a 10-15-min span of embryonic development and may be regulating the timing of crucial cell divisions at this early stage of development.     

A spatially and temporally restricted mouse model of soft tissue sarcoma

Soft tissue sarcomas are mesenchymal tumors that are fatal in approximately one-third of patients. To explore mechanisms of sarcoma pathogenesis, we have generated a mouse model of soft tissue sarcoma. Intramuscular delivery of an adenovirus expressing Cre recombinase in mice with conditional mutations in Kras and Trp53 was sufficient to initiate high-grade sarcomas with myofibroblastic differentiation. Like human sarcomas, these tumors show a predilection for lung rather than lymph node metastasis. Using this model, we showed that a prototype handheld imaging device can identify residual tumor during intraoperative molecular imaging. Deletion of the Ink4a-Arf locus (Cdkn2a), but not Bak1 and Bax, could substitute for mutation of Trp53 in this model. Deletion of Bak1 and Bax, however, was able to substitute for mutation of Trp53 in the development of sinonasal adenocarcinoma. Therefore, the intrinsic pathway of apoptosis seems sufficient to mediate p53 tumor suppression in an epithelial cancer, but not in this model of soft tissue sarcoma.     

Heart failure progression is accelerated following myocardial infarction in type 2 diabetic rats

Clinical studies have shown a greater incidence of myocardial infarction in diabetic patients, and following an infarction, diabetes is associated with an increased risk for the development of left ventricular (LV) dysfunction and heart failure. The goal of this study was to determine if the progression of heart failure following myocardial infarction in type 2 diabetic (T2D) rats is accelerated compared with nondiabetic rats. Male nondiabetic Wistar-Kyoto (WKY) and T2D Goto-Kakizaki (GK) rats underwent coronary artery ligation or sham surgery to induce heart failure. Postligation (8 and 20 wk), two-dimensional echocardiography and LV pressure measurements were made. Heart failure progression, as assessed by enhanced LV remodeling and contractile dysfunction, was accelerated 8 wk postligation in the T2D animals. LV remodeling was evident from increased end-diastolic and end-systolic diameters and areas in the GK compared with the WKY infarcted group. Furthermore, enhanced LV contractile dysfunction was evident from a greater deterioration in fractional shortening and enhanced myocardial performance index (an index of global LV dysfunction) in the GK infarcted group. This accelerated progression was accompanied by greater increases in atrial natriuretic factor and skeletal alpha-actin (gene markers of heart failure and hypertrophy) mRNA levels in GK infarcted hearts. Despite similar decreases in metabolic gene expression (i.e., peroxisome proliferator-activated receptor-alpha-regulated genes associated with fatty acid oxidation) between infarcted WKY and GK rat hearts, myocardial triglyceride levels were elevated in the GK hearts only. These results, demonstrating enhanced remodeling and LV dysfunction 8 wk postligation provide evidence of an accelerated progression of heart failure in T2D rats.     

Monoclonal antibodies show that kinase C phosphorylation of GAP-43 during axonogenesis is both spatially and temporally restricted in vivo.

To study the role of kinase C phosphorylation in the distribution and function of GAP-43 we have generated a panel of mAbs that distinguish between GAP-43 that has been phosphorylated by kinase C and forms that have not. One class of antibodies, typified by 2G12/C7, reacts with only the phosphorylated form of GAP-43; it recognizes the peptide IQAS(PO4)FR equivalent to residues 38-43 that includes the single kinase C phosphorylation site at serine. Another, exemplified by 10E8/E7, reacts with both phosphorylated and nonphosphorylated forms. We have used the antibodies to study the distribution of kinase C-phosphorylated GAP-43 during axonogenesis and in the adult nervous system. Two major findings emerge. First, there is a lag between the initiation of axon outgrowth and the phosphorylation of GAP-43 by kinase C. The extent of this lag period varies between the different structures studied. In some cases, e.g., the trigeminal nerve, our result suggest that kinase C phosphorylation may be correlated with proximity of the growing axon to its target. Second, kinase C-phosphorylated GAP-43 is always spatially restricted to the distal axon. It is never seen either proximally or in cell bodies, even those with high levels of GAP-43 protein. This result also implies that GAP-43 is axonally transported in the non-kinase C phosphorylated form. Thus, kinase C phosphorylation of GAP-43 is not required for axon outgrowth or growth cone function per se and may be more related to interactions of the growth cone with its environment.     

Serum prolactin levels in rats following isoproterenol-induced myocardial infarction.

Circulating prolactin levels were monitored in nonarteriosclerotic, arteriosclerotic, and hormonally sterilized male and female Sprague-Dawley rats during the acute necrosis and repair phases of myocardial infarction induced by isoproterenol. Male rats are particularly prone to succumb to acute myocardial ischemia but reduction of androgen levels by neonatal sterilization improved survival considerably. Circulating prolactin levels are greatly increased, particularly in females, during acute myocardial ischemia. Since androgens suppress the hypothalamic center for prolactin release, prolactin levels were delayed and transitory in males. It is suggested that the superior survival of female rats may be related to their greater production of prolactin during acute stages of myocardial ischemia, which would dampen the tachycardia-inducing effects of the potent beta-adrenergic stimulating agent, isoproterenol.     

Carbon dioxide fluxes in a spatially and temporally heterogeneous temperate grassland

Landscape position, grazing, and seasonal variation in precipitation and temperature create spatial and temporal variability in soil processes, and plant biomass and composition in grasslands. However, it is unclear how this variation in plant and soil properties affects carbon dioxide (CO₂) fluxes. The aim of this study is to explore the effect of grazing, topographic position, and seasonal variation in soil moisture and temperature on plant assimilation, shoot and soil respiration, and net ecosystem CO₂ exchange (NEE). Carbon dioxide fluxes, vegetation, and environmental variables were measured once a month inside and outside long-term ungulate exclosures in hilltop (dry) to slope bottom (mesic) grassland throughout the 2004 growing season in Yellowstone National Park. There was no difference in vegetation properties and CO₂ fluxes between the grazed and the ungrazed sites. The spatial and temporal variability in CO₂ fluxes were related to differences in aboveground biomass and total shoot nitrogen content, which were both related to variability in soil moisture. All sites were CO₂ sinks (NEE>0) for all our measurments taken throughout the growing season; but CO₂ fluxes were four- to fivefold higher at sites supporting the most aboveground biomass located at slope bottoms, compared to the sites with low biomass located at hilltops or slopes. The dry sites assimilated more CO₂ per gram aboveground biomass and stored proportionally more of the gross-assimilated CO₂ in the soil, compared to wet sites. These results indicate large spatio-temporal variability of CO₂ fluxes and suggest factors that control the variability in Yellowstone National Park.     

Phosphorylation of NDRG1 is temporally and spatially controlled during the cell cycle

The tumour metastasis suppressor, N-myc Downstream Regulated Gene (NDRG) 1, is a by the protein kinases SGK1 and GSK3β, but the relevance of its phosphorylation remains unclear. Analysis of HCT116 cells, either proficient or deficient for p53 revealed NDRG1 protein expression and phosphorylation by SGK1 was increased basally in p53-deficient cells. Treatment with the cell cycle inhibitors, aphidicolin or nocodazole also revealed increased NDRG1 phosphorylation in p53-deficient cells. Finally, phosphorylated NDRG1 was found to co-localise with γ-tubulin on centromeres and also to the cleavage furrow during cytokinesis. Taken together, this work demonstrates that NDRG1 phosphorylation, by the protein kinase SGK1, is temporally and spatially controlled during the cell cycle, suggesting a role for NDRG1 in successful mitosis.     

Alternative splicing of the Drosophila Dscam pre-mRNA is both temporally and spatially regulated

The Drosophila melanogaster Down syndrome cell adhesion molecule (Dscam) gene encodes an axon guidance receptor that can express 38,016 different mRNAs by virtue of alternative splicing. The Dscam gene contains 95 alternative exons that are organized into four clusters of 12, 48, 33, and 2 exons each. Although numerous Dscam mRNA isoforms can be synthesized, it remains to be determined whether different Dscam isoforms are synthesized at different times in development or in different tissues. We have investigated the alternative splicing of the Dscam exon 4 cluster, which contains 12 mutually exclusive alternative exons, and found that Dscam exon 4 alternative splicing is developmentally regulated. The most highly regulated exon, 4.2, is infrequently used in early embryos but is the predominant exon 4 variant used in adults. Moreover, the developmental regulation of exon 4.2 alternative splicing is conserved in D. yakuba. In addition, different adult tissues express distinct collections of Dscam mRNA isoforms. Given the role of Dscam in neural development, these results suggest that the regulation of alternative splicing plays an important role in determining the specificity of neuronal wiring. In addition, this work provides a framework to determine the mechanisms by which complex alternative splicing events are regulated.     

HMGB1, an architectural chromatin protein and extracellular signalling factor,has a spatially and temporally restricted expression pattern in mouse brain

HMGB1 is an abundant chromatin component, so far considered ubiquitous. HMGB1 also has an extracellular signalling role: when passively released by necrotic cells, it triggers inflammation; moreover, it can be actively secreted by myeloid cells, neurons and neuronal cancer cells. We show here that HMGB1 protein is undetectable in most cells in adult mouse brain, and is present in a subset of brain cells during development, with a very complex temporal, spatial and subcellular expression pattern. HMGB1 is expressed in the cortical plate of E14.5 embryos, predominantly in the nucleus, although roughly 1% of cells show a cytoplasmic localization as well. In E16 embryos, HMGB1 is nuclearly expressed in scattered cells apparently moving from the ventricular zone to the cortical plate. HMGB1 expression is strongly down-regulated at later developmental stages; in adult mice significant expression is maintained only in areas of continuing neurogenesis. Finally, HMGB1 subcellular localization changes during retinoic acid induced differentiation of P19 neuroblastoma cells.     

Perception of the consequences of self-action is temporally tuned and event driven

It has been proposed that in order to increase the salience of sensations with an external cause, sensations that are predictable based on one's own actions are attenuated [1 and 2]. This may explain why self-imposed tickle [3 and 4] or constant forces [5] are perceived as less intense than the same stimuli externally imposed. Here, subjects used their right index finger to tap a force sensor mounted above their left index finger. When a motor generated a tap on the left finger synchronously with the right tap, simulating contact between the fingers, the perception of force in the left finger was attenuated compared to the same tap experienced during rest. Attenuation gradually reduced as the left tap was either delayed or advanced relative to the active right tap. However, no attenuation was seen to left taps triggered by right-finger movements that stopped above or passed wide of the sensor. We conclude that there is a window of sensory attenuation that is broadly temporally tuned and centered on the time at which the fingers would normally make contact. That is, predictive tactile sensory attenuation is linked to specific external events arising from movement rather than to the movement per se.     

Evolutionarily stable dispersal of a waterstrider in a temporally and spatially heterogeneous environment

Summary Evolutionary stable dispersal and wing muscle histolysis strategies are studied in the waterstriderGerris thoracicus. These strategies relate to spreading reproductive risk. Overwintering individuals have the choice of dispersing to either a brackish sea bay or a rock pool habitat. The former is reproductively more favorable than the latter during warm dry years and less favorable during cool wet years. After spring migration, individuals may histolyse their flight muscles and lay all their eggs in one pool or they may retain their flight ability and lay fewer eggs in total but spread them in several pools. We use a simple two-habitat model to examine the question of habitat dispersal. Our results indicate that, although the value of the evolutionary stable dispersal depends on the degree of variability in the environment and on the probability of local extinctions in either habitat, the population always disperses to both habitats as a consequence of density dependent growth. We use a more detailed multiple-rockpool habitat model to examine the question of wing muscle histolysis as a response to density dependence. Our results indicate that a wing muscle histolysis response to population density is an evolutionarily stable strategy when compared with the two alternatives of females always histolysing or never histolysing their flight muscles. The application of evolutionarily stable theory to stochastic problems presents a number of difficulties. We discuss these difficulties in the context of computing evolutionarily stable strategies for the problems at hand.     

Competence to develop sensory organs is temporally and spatially regulated in Drosophila epidermal primordia.

The Drosophila adult cuticle displays a stereotyped pattern of sensory organs (SOs). Its deployment requires the expression of the achaete (ac) and scute (sc) genes. Their products confer to cells of epidermal primordia (imaginal discs and histoblasts) the ability to become SO precursors (SOPs). In imaginal discs, ac and sc expression is spatially restricted to cell clusters within which one or a few cells become SOP(s). With the help of ubiquitous sc expression provided at different developmental times by a heat shock-sc (HSSC) chimeric gene, we have analyzed the response of epidermal primordia to the proneural action of the sc product, and have tested whether the patterned distribution of ac/sc products is necessary to position SOs correctly within the epidermis. Each primordium responds to HSSC expression by developing SOs only during a characteristic developmental period. In the absence of the endogenous ac and sc genes, most SOs induced by HSSC are of the correct type and are located in wild type positions. These results indicate that the capacity of primordia to respond to sc is temporally and spatially regulated, that specification of the type of SO does not depend on ac/sc, and that SO positioning utilizes topological information independent of the spatially restricted distribution of ac/sc products.     

Predictive models in spatially and temporally variable freshwater systems

Abstract This paper discusses the relationships between scaling and predictability in ecosystems. The logical basis of ecosystem modelling is explored using ideas first developed in complexity theory and analogies with the behaviour of complex adaptive systems. Any ecological model is a scale-dependent entity and both empirical and dynamic models of freshwater systems have their strengths and weaknesses. The logical basis of modelling using functional groups is explored. I conclude that such an approach can be justified and that such models have predictive power. Any predictive model of freshwater systems must take the major scales of external (atmospheric and catchment) forcing into account as well as the scales of key processes in the ecosystem itself. The importance of so-called ‘pink noise’ spectra, which arise both from external forcing and the internal dynamics of dynamic systems, is noted. The key scales of pattern and process in freshwater ecosystems are discussed in relation to the properties of the major functional groups. In order to have predictive power, I conclude that models of freshwater systems must include sediment exchanges and the properties of aquatic macrophytes as well as water column interactions and the pelagic components. When viewed at the scale of functional groups and the major biogeochemical processes, freshwater ecosystems may not be as complex as is often assumed.     

Nestin-expressing neural stem cells identified in the scar following myocardial infarction

Nerve fiber innervation of the scar following myocardial damage may have occurred either via the growth of pre-existing fibers and/or the mobilization of neural stem cells. The present study examined whether neural stem cells were recruited to the infarct region of the rat heart following coronary artery ligation. The neural stem cell marker nestin was detected in the infarct region of 1-week post-myocardial infarct (MI) male rats and cultured scar-derived neural-like cells. By contrast, nestin staining was undetected in either scar myofibroblasts or cardiac myocytes residing in the non-infarcted left ventricle. Reactive astrocytes were isolated from the infarct region and characterized by the co-expression of nestin, glial fibrillary acidic protein, and vimentin. Specific staining of oligodendrocytes and neurons was also detected in the infarct region and cultured scar-derived neural-like cells. Furthermore, neurofilament-M positive fibers were identified in the scar and tyrosine hydroxylase immunoreactivity was observed in peripherin-positive neurons. Neurite formation was induced in PC12 cells treated with the conditioned-media of primary passage scar-derived cells, highlighting the synthesis and secretion of neurotrophic factors. Nerve growth factor (NGF) and brain-derived neurotrophic factor were detected in myofibroblasts and neural cells, and both cell types expressed the NGF receptors trkA and p75. These data highlight the novel observation that neural stem cells were recruited to the infarct region of the damaged rat heart and may contribute in part to nerve fiber growth and subsequent innervation of the scar.     

Localization of human Mcm10 is spatially and temporally regulated during the S phase

Mcm10 (Dna43) is an essential protein for the initiation of DNA replication in Saccharomyces cerevisiae. Recently, we identified a human Mcm10 homolog and found that it is regulated by proteolysis and phosphorylation in a cell cycle-dependent manner and that it binds chromatin exclusively during the S phase of the cell cycle. However, the precise roles that Mcm10 plays are still unknown. To study the localization dynamics of human Mcm10, we established HeLa cell lines expressing green fluorescent protein (GFP)-tagged Mcm10. From early to mid-S phase, GFP-Mcm10 appeared in discrete nuclear foci. In early S phase, several hundred foci appeared throughout the nucleus. In mid-S phase, the foci appeared at the nuclear periphery and nucleolar regions. In the late S and G phases, GFP-Mcm10 was localized to nucleoli. Although (2)the distributions of GFP-Mcm10 during the S phase resembled those of replication foci, GFP-Mcm10 foci did not colocalize with sites of DNA synthesis in most cases. Furthermore, the transition of GFP-Mcm10 distribution patterns preceded changes in replication foci patterns or proliferating cell nuclear antigen foci patterns by 30-60 min. These results suggest that human Mcm10 is temporarily recruited to the replication sites 30-60 min before they replicate and that it dissociates from chromatin after the activation of the prereplication complex.     

popRange: a highly flexible spatially and temporally explicit Wright-Fisher simulator

Background

Sequencing and genotyping technology advancements have led to massive, growing repositories of spatially explicit genetic data and increasing quantities of temporal data (i.e., ancient DNA). These data will allow more complex and fine-scale inferences about population history than ever before; however, new methods are needed to test complex hypotheses.

Results

This article presents popRange, a forward genetic simulator, which incorporates large-scale genetic data with stochastic spatially and temporally explicit demographic and selective models. Features such as spatially and temporally variable selection coefficients and demography are incorporated in a highly flexible manner. popRange is implemented as an R package and presented with an example simulation exploring a selected allele’s trajectory in multiple subpopulations.

Conclusions

popRange allows researchers to evaluate and test complex scenarios by simulating large-scale data with complicated demographic and selective features. popRange is available for download at http://cran.r-project.org/web/packages/popRange/index.html.

     

Changes in fatty acid compositions of myocardial lipids in rats with heart failure following myocardial infarction

Changes in fatty acid composition of myocardial lipids were examined in rats with heart failure following myocardial infarction. Left ventricular systolic pressure (LVSP) was decreased and left ventricular end-diastolic pressure (LVEDP) was elevated 24 h, 1 and 12 weeks after left coronary artery ligation (CAL), suggesting the development of heart failure at these periods in this model. Hearts were isolated 24 h, 1 week and 12 weeks after the operation. Myocardial lipids in the infarcted scar tissue, non-infarcted remaining left ventricle including interseptum and right ventricle were separated into phospholipid (PL), triacylglycerol (TG), diacylglycerol (DAG) and free fatty acid (FFA) fractions. In the scar tissue PL content markedly decreased whereas TG, DAG and FFA contents increased 24 h after CAL. Despite a marked decrease in constituted fatty acids of PL fraction in the scar tissue the percentage of arachidonic acid in PL was elevated 12 weeks after CAL, suggesting that release of arachidonic acid during PL degradation was suppressed. In the non-infarcted viable left ventricle PL content remained unchanged throughout the experiment whereas TG, DAG and FFA contents were elevated 24 h after CAL. Despite no changes in PL and other lipid contents in the non-infarcted tissue the percentage of linoleic acid in PL was reduced and that of docosahexaenoic acid in PL was elevated 12 weeks after CAL. Our findings showed that myocardial lipid composition of the non-infarcted left ventricle was altered only in an early stage of the development of heart failure and fatty acid compositions of PL was exchanged in a late stage of the development of heart failure. The exchange may be related to cardiac dysfunction or myocardial remodelling in the rat with heart failure.     

Fission yeast cells undergo nuclear division in the absence of spindle microtubules

Mitosis in eukaryotic cells employs spindle microtubules to drive accurate chromosome segregation at cell division. Cells lacking spindle microtubules arrest in mitosis due to a spindle checkpoint that delays mitotic progression until all chromosomes have achieved stable bipolar attachment to spindle microtubules. In fission yeast, mitosis occurs within an intact nuclear membrane with the mitotic spindle elongating between the spindle pole bodies. We show here that in fission yeast interference with mitotic spindle formation delays mitosis only briefly and cells proceed to an unusual nuclear division process we term nuclear fission, during which cells perform some chromosome segregation and efficiently enter S-phase of the next cell cycle. Nuclear fission is blocked if spindle pole body maturation or sister chromatid separation cannot take place or if actin polymerization is inhibited. We suggest that this process exhibits vestiges of a primitive nuclear division process independent of spindle microtubules, possibly reflecting an evolutionary intermediate state between bacterial and Archeal chromosome segregation where the nucleoid divides without a spindle and a microtubule spindle-based eukaryotic mitosis.