Seasonal variations in the metabolic rates of zooplankton populations in a Thames Valley reservoir

Measurements of metabolic rates of natural populations of zooplankton were made using a closed bottle technique in situ. Results showed a marked seasonality inexplicable in terms of simple temperature functions. For this cladoceran dominated zooplankton, seasonal variations in metabolic response are attributed to a degree of temperature acclimation, to changes in the size structure and species composition of the populations and seasonal variations in food sources.     

Cybernetic modeling of iron-limited growth and siderophore production

The cybernetic modeling framework developed by Ramkrishna and co-workers has been applied to a case of bacterial metabolite production, namely the production of siderophores (iron-chelating agents) associated with iron-limiting fermentation conditions. Experimental growth data showed that, even though final biomass levels were controlled by exhaustion of the carbon source, iron-limiting conditions also affected the biomass yield. A structured model which includes the process of an iron-limiting energy resource production was able to quantitatively account for this apparent dual-substrate limitation over a wide range of batch and continuous operating conditions. The experiments data also showed quite large difference in iron uptake over the wide range of operating condition and iron levels investigated. The inclusion in the model of the processes of low and high (siderophore-mediated) affinity iron transport, and siderophore production led to simulation results that were in good quantitative agreement with the siderophore, medium and cell iron levels, in both batch and steady-state continuous culture operating conditions.     

Monolayer culture of parenchymal rat hepatocytes on collagen-coated microcarriers. A hepatocyte system for short- and long-term metabolic studies

Summary A method is described for the attachment to and monolayer culture of adult rat hepatocytes on collagen-coated or fibronectin-coated microbeads or both in a chemically defined serum-free medium. Protein synthesis measured by the incorporation of [³H]leucine into protein was four-fold higher in the hepatocyte microcarrier cultures than in isolated hepatocyte suspensions. The hepatocyte microcarrier cultures showed acute responsiveness to insulin of fatty acid synthesis, glucose incorporation into glycogen, and decarboxylation of [1-¹⁴C]pyruvate. Microcarrier-cultured hepatocytes have the combined advantages of monolayer culture and suspension systems. They are a potential tool for the study of long-term as well as acute effects of hormones. This work was supported by the British Diabetic Association.     

Morphologic analysis of long-term bone marrow cultures that support B-lymphopoiesis or myelopoiesis

Summary A comparative morphological analysis of the Whitlock-Witte long-term B-cell culture and the predominantly myeloid Dexter long-term bone marrow culture demonstrates that similarities and differences exist between the two systems. Cells from the long-term B-cell cultures have a characteristic lymphoid morphology, whereas those from the Dexter cultures are predominantly granulocytes and macrophages along with a few undifferentiated blast cells. A multilayered stromal cell layer is a common feature of both systems. Scanning electron micrographs show the cells in this layer to be large, irregularly shaped and flattened. The data further indicate that there are unique features in the relationship between developing B cells and stromal cells in the long-term B-cell cultures. Large, mononuclear cells are present that have numerous membrane infoldings within which numerous lymphoid cells lie. The relationship of these cells to macrophages and epithelial/reticular cells is discussed.Supported by the National Institutes of Health Grants AI2125601 (KD) and HD13704 (WHF)     

Extreme water efficiency of Cape gannet Morus capensis chicks as an adaptation to water scarcity and heat stress in the breeding colony

Cape gannet Morus capensis chicks depend entirely on fish prey and metabolic water for water requirements during development. Water loss through evaporative cooling due to heat stress is substantial. We measured water flux and field metabolic rates (FMR) of Cape gannet chicks and adults to determine if gannets developed water saving strategies. The water economy index (WEI, g kJ^?1) decreased with chick age according to the model WEI = 0.676 – 0.272 × log₁₀(t), indicating that water efficiency increased with age. At fledging, the WEI of chicks was at the level expected of adult desert birds. Desert birds maintain a low WEI by also having a low FMR, whereas Cape gannet chicks have FMR comparable to other seabird species’ nestling requirements. We propose that maintaining low WEI is adaptive for Cape gannets because (1) chicks need to balance water loss through evaporative cooling, (2) fledglings need to overcome a period of up to a week when they cannot ingest any water and (3) adults spend extended periods in the breeding colony during which water can become a limiting factor. Understanding the physiological mechanism of maintaining low WEI will become increasingly important with future rising temperatures.     

BNIP3L/NIX-dependent mitophagy regulates cell differentiation via metabolic reprogramming

Macroautophagy/autophagy is the process by which cellular components are degraded and recycled within the lysosome. These components include mitochondria, the selective degradation of which is known as mitophagy. Mitochondria are dynamic organelles that constantly adapt their morphology, function, and number to accommodate the metabolic needs of the cell. Extensive metabolic reconfiguration occurs during cell differentiation, when mitochondrial activity increases in most cell types. However, our data demonstrate that during physiologic retinal ganglion cell (RGC) development, mitophagy-dependent metabolic reprogramming toward glycolysis regulates numbers of RGCs, which are the first neurons to differentiate in the retina and whose axons form the optic nerve. We show that during retinal development tissue hypoxia triggers HIF1A/HIF-1 stabilization, resulting in increased expression of the mitophagy receptor BNIP3L/NIX. BNIP3L-dependent mitophagy results in a metabolic shift toward glycolysis essential for RGC neurogenesis. Moreover, we demonstrate that BNIP3L-dependent mitophagy also regulates the polarization of proinflammatory/M1 macrophages, which undergo glycolysis-dependent differentiation during the inflammatory response. Our results uncover a new link between hypoxia, mitophagy, and metabolic reprogramming in the differentiation of several cell types in vivo. These findings may have important implications for neurodegenerative, metabolic and other diseases in which mitochondrial dysfunction and metabolic alterations play a prominent role.     

Studying the “fly factor” phenomenon and its underlying mechanisms in house flies Musca domestica

The “fly factor” was first discovered >60 years ago and describes the phenomenon that food currently or previously fed on by flies attracts more foraging flies than the same type and amount of food kept inaccessible to flies. Since then, there has been little progress made to understanding this phenomenon. Our objectives were (i) to demonstrate the existence of the fly factor in house flies, Musca domestica and (ii) to study underlying mechanisms that may cause or contribute to the fly factor. In 2‐choice laboratory bioassays, we obtained unambiguous evidence for a fly factor phenomenon in house flies, in that we demonstrated that feeding flies are more attractive to foraging flies than are nonfeeding flies, and that fed‐on food is more attractive to foraging flies than is “clean” food. Of the potential mechanisms (fly excreta, metabolic output parameters [elevated temperature, relative humidity, carbon dioxide]), causing the fly factor, fly feces, and regurgitate do attract foraging flies but none of the metabolic output parameters of feeding flies does. Even though feeding flies produce significantly more CO₂ than nonfeeding flies, elevated levels of CO₂ have no behavior‐modifying effect on flies. Preferential attraction of house flies to fly feces and regurgitate indicates that the flies sense airborne semiochemicals emanating from these sources. Hypothesizing that these semiochemicals are microbe‐produced, future studies will aim at isolating and mass producing these microbes to accumulate semiochemicals for identification.     

Discoidin domain receptors: Microenvironment sensors that promote cellular migration and invasion

ABSTRACT

Extracellular matrix (ECM) provides cells scaffolding for cell migration and microenvironment for various cellular functions. Collagens are major ECM components in tissue and discoidin domain receptors (DDRs) are receptor tyrosine kinases (RTK) that recognise fibrillar collagens. Unlike other RTK, their ligands are solid ECM the that are abundantly present in the pericellular environment in various tissue, and thus its activation and regulations are unique amongst RTK family. It is emerging that DDRs may be the sensors that monitor and detects changes in ECM microenvironment and determines the cellular fates upon tissue injuries. In this mini-review, recent findings on the role of DDRs as microenvironment sensor and their roles in cell migration and invasion are discussed.