Mediation of pinocytosis in cultured arterial smooth muscle and endothelial cells by platelet-derived growth factor

Pinocytosis was measured in monkey aortic smooth muscle cells (SMC), bovine aortic endothelial cells, and Swiss 3T3 cells in culture as cellular uptake of [U-(14)C]sucrose and horseradish peroxidase (HRP) from the tissue culture medium. Monkey arterial SMC and Swiss 3T3 cells were maintained in a quiescent state of growth at low cells density in medium containing 5 percent monkey plasma-derived serum (PDS). Replacement of PDS with 5 percent monkey whole blood serum (WBS) from the same donor, or addition to PDS of partially purified platelet-derived growth factor(s) (PF), resulted in a marked stimulation of pinocytosis as well as of cellular proliferation. In SMC, enhancement of the rate of pinocytosis occurred 4-6 h after exposure to WBS or PF, and the rate was up to twofold higher than the rate in medium containing PDS. In contrast, [(3)H]thymidine uptake by SMC did not increase until 12-16 h after exposure to PF. In endothelial cells the presence of PF or WBS did not enhance either the rate of pinocytosis or the rate of proliferation over that in PDS. Thus, endothelial cells did not become quiescent at subconfluent densities in PDS but maintained rates of proliferation and pinocytosis that were equivalent to those in WBS. By autoradiography, the fraction of labeled nuclei in SMC cultures 24 h after change of medium increased from 0.061 +/- 0.004 in quiescent cultures to 0.313 +/- 0.028 after exposure to WBS or PF. In contrast, labeling indices of endothelial cells were similar for cultures grown in PDS, WBS, or PF at any single time point after change of medium. These findings suggest that the rate of pinocytosis maybe be coupled in some fashion to growth regulation, which may be mediated in part by specific growth factors, such as that derived from the thrombocyte.     

Competitive abilities of three narrowly endemic plant species in experimental neighborhoods along a fire gradient

We conducted field experiments manipulating lichens, shrubs, and herbs along a time-since-fire gradient and assessing effects on three endemic herbaceous species of Florida scrub: Eryngium cuneifolium, Hypericum cumulicola, and Polygonella basiramia. Responses included seed germination, survival, biomass, and fecundity. Transplants into recently burned patches generally had higher survival, larger biomass, and greater reproductive output than transplants into long-unburned patches. Open areas and sites near oaks frequently were more favorable than sites near Florida rosemary. Ground lichens did not affect germination but increased mortality rate of seedlings. Neighboring small shrubby and herbaceous species did not affect the performance of these species. Of the three species, naturally occurring E. cuneifolium were farthest from large shrubs, and their microhabitats had the least ground lichens and shrubs. Eryngium cuneifolium and H. cumulicola are capable of forming persistent seed banks and their recruitment after fire depends mostly on these dormant seeds. Polygonella basiramia relies on seed dispersal and immediate seed germination to colonize recently burned patches. Management for these species should involve variable fire regimes to allow all three species to persist along with many other scrub endemics.     

Control of stem cell fate by engineering their micro and nanoenvironment

Stem cells are capable of long-term self-renewal and differentiation into specialised cell types, making them an ideal candidate for a cell source for regenerative medicine. The control of stem cell fate has become a major area of interest in the field of regenerative medicine and therapeutic intervention. Conventional methods of chemically inducing stem cells into specific lineages is being challenged by the advances in biomaterial technology, with evidence highlighting that material properties are capable of driving stem cell fate. Materials are being designed to mimic the clues stem cells receive in their in vivo stem cell niche including topographical and chemical instructions. Nanotopographical clues that mimic the extracellular matrix(ECM) in vivo have shown to regulate stem cell differentiation. The delivery of ECM components on biomaterials in the form of short peptides sequences has also proved successful in directing stem cell lineage. Growth factors responsible for controlling stem cell fate in vivo have also been delivered via biomaterials to provide clues to determine stem cell differentiation. An alternative approach to guide stem cells fate is to provide genetic clues including delivering DNA plasmids and small interfering RNAs via scaffolds. This review, aims to provide an overview of the topographical, chemical and molecular clues that biomaterials can provide to guide stem cell fate. The promising features and challenges of such approaches will be highlighted, to provide directions for future advancements in this exciting area of stem cell translation for regenerative medicine.     

How do plant ecologists use matrix population models?

Matrix projection models are among the most widely used tools in plant ecology. However, the way in which plant ecologists use and interpret these models differs from the way in which they are presented in the broader academic literature. In contrast to calls from earlier reviews, most studies of plant populations are based on < 5 matrices and present simple metrics such as deterministic population growth rates. However, plant ecologists also cautioned against literal interpretation of model predictions. Although academic studies have emphasized testing quantitative model predictions, such forecasts are not the way in which plant ecologists find matrix models to be most useful. Improving forecasting ability would necessitate increased model complexity and longer studies. Therefore, in addition to longer term studies with better links to environmental drivers, priorities for research include critically evaluating relative/comparative uses of matrix models and asking how we can use many short-term studies to understand long-term population dynamics.     

Genetic covariance between indices of body condition and immunocompetence in a passerine bird

Background  

Condition-dependence is a ubiquitous feature of animal life histories and has important implications for both natural and sexual selection. Mate choice, for instance, is typically based on condition-dependent signals. Theory predicts that one reason why condition-dependent signals may be special is that they allow females to scan for genes that confer high parasite resistance. Such explanations require a genetic link between immunocompetence and body condition, but existing evidence is limited to phenotypic associations. It remains unknown, therefore, whether females selecting males with good body condition simply obtain a healthy mate, or if they acquire genes for their offspring that confer high immunocompetence.     

Fire-mediated effects of shrubs, lichens and herbs on the demography of Hypericum cumulicola in patchy Florida scrub

Understanding the effect of disturbance and interspecific interactions on population dynamics and availability of suitable habitats for colonization and growth is critical for conservation and management of endangered species. Hypericum cumulicola is a narrowly endemic, small perennial herb virtually restricted to open areas of well-drained white sand in Florida rosemary scrub, a naturally patchy community that burns about every 20–80 years. Over 1 year (September 1994 to September 1995) we evaluated variation in survival, growth and fecundity among 1214 individuals in 14 rosemary scrub patches of different sizes (0.09–1.85 ha) and fire histories (2, 8–10, and >20 years since the last fire). Fire kills aboveground individuals of H. cumulicola, but new individuals were present a year after fire. Recruitment decreased in patches more than a decade post-fire. Survival, annual height growth rate, and fecundity (number of flowers and fruits) were higher in recently burned patches. Scrub patch size did not affect these demographic variables. Survival was positively associated with the presence of conspecifics and negatively related to proximity to the dominant shrub Florida rosemary (Ceratiola ericoides), prior reproductive output, and ground lichen cover. Since H. cumulicola and other herbaceous species in the rosemary scrub depend on sporadic fires to decrease interference of shrubs and ground lichens, its persistence may be threatened by fire suppression. Received: 4 December 1996 / Accepted: 5 June 1997     

Habitat and microsite influence demography of two herbs in intact and degraded scrub

Identifying environmental factors associated with vital rate variation is critical to predict population consequences of environmental perturbation. We used matrix models to explore effects of habitat and microsite on demography of two widespread herbs, Chamaecrista fasciculata (partridge pea) and Balduina angustifolia (yellow buttons). We evaluated models simulating population dynamics in common microsites (shrub, litter, bare sand) within two habitats (intact, degraded Florida scrub) using data on experimental populations initiated by sowing seeds, and natural seed production. Models included four stages (seed bank, small vegetative, large vegetative, reproductive) and three vital rates (survival, growth, fecundity), summarized in sixteen transitions. We conducted life table response experiments to assess contributions of each habitat and microsite to population growth rates. We found that (1) C. fasciculata had greatest population growth in degraded habitat and litter microsites, (2) B. angustifolia had similar population growth between habitats and greatest in bare sand microsites, (3) advancing growth transitions of C. fasciculata had greatest elasticity on population growth in degraded habitat, shrub, and litter, as did seed survival in intact habitat and bare sand, (4) seed survival and advancing growth transitions of B. angustifolia had greatest elasticity on population growth in both habitats, as did seed survival in shrub and litter, and advancing growth in bare sand. Greater population growth of C. fasciculata in degraded scrub is probably explained by release from belowground competition; B. angustifolia may be most affected by competition with shrubs. Microsites in intact scrub were not ecologically equivalent to those in degraded scrub emphasizing that intact scrub is ecologically complex and critical to preserve.