Locomotion in caterpillars

Most species of caterpillar move around by inching or crawling. Their ability to navigate in branching three‐dimensional structures makes them particularly interesting biomechanical subjects. The mechanism of inching has not been investigated in detail, but crawling is now well understood from studies on caterpillar neural activity, dynamics and structural mechanics. Early papers describe caterpillar crawling as legged peristalsis, but recent work suggests that caterpillars use a tension‐based mechanism that helps them to exploit arboreal niches. Caterpillars are not obligate hydrostats but instead use their strong grip to the substrate to transmit forces, in effect using their environment as a skeleton. In addition, the gut which accounts for a substantial part of the caterpillar's weight, moves independently of the body wall during locomotion and may contribute to crawling dynamics. Work‐loop analysis of caterpillar muscles shows that they are likely to act both as actuators and energy dissipaters during crawling. Because caterpillar tissues are pseudo‐elastic, and locomotion involves large body deformations, moving is energetically inefficient. Possession of a soft body benefits caterpillars by allowing them to grow quickly and to access remote food sources safely.     

High-throughput Analysis of Mammalian Olfactory Receptors: Measurement of Receptor Activation via Luciferase Activity

Odorants create unique and overlapping patterns of olfactory receptor activation, allowing a family of approximately 1,000 murine and 400 human receptors to recognize thousands of odorants. Odorant ligands have been published for fewer than 6% of human receptors^1-11. This lack of data is due in part to difficulties functionally expressing these receptors in heterologous systems. Here, we describe a method for expressing the majority of the olfactory receptor family in Hana3A cells, followed by high-throughput assessment of olfactory receptor activation using a luciferase reporter assay. This assay can be used to (1) screen panels of odorants against panels of olfactory receptors; (2) confirm odorant/receptor interaction via dose response curves; and (3) compare receptor activation levels among receptor variants. In our sample data, 328 olfactory receptors were screened against 26 odorants. Odorant/receptor pairs with varying response scores were selected and tested in dose response. These data indicate that a screen is an effective method to enrich for odorant/receptor pairs that will pass a dose response experiment, i.e. receptors that have a bona fide response to an odorant. Therefore, this high-throughput luciferase assay is an effective method to characterize olfactory receptors—an essential step toward a model of odor coding in the mammalian olfactory system.     

Consistent temperature dependence of respiration across ecosystems contrasting in thermal history

Ecosystem respiration is a primary component of the carbon cycle and understanding the mechanisms that determine its temperature dependence will be important for predicting how rates of carbon efflux might respond to global warming. We used a rare model system, comprising a network of geothermally heated streams ranging in temperature from 5 °C to 25 °C, to explore the nature of the relationship between respiration and temperature. Using this ‘natural experiment’, we tested whether the natal thermal regime of stream communities influenced the temperature dependence of respiration in the absence of other potentially confounding variables. An empirical survey of 13 streams across the thermal gradient revealed that the temperature dependence of whole‐stream respiration was equivalent to the average activation energy of the respiratory complex (0.6–0.7 eV). This observation was also consistent for in‐situ benthic respiration. Laboratory experiments, incubating biofilms from four streams across the thermal gradient at a range of temperatures, revealed that the activation energy and Q₁₀ of respiration were remarkably consistent across streams, despite marked differences in their thermal history and significant turnover in species composition. Furthermore, absolute rates of respiration at standardised temperature were also unrelated to ambient stream temperature, but strongly reflected differences in biofilm biomass. Together, our results suggest that the core biochemistry, which drives the kinetics of oxidative respiratory metabolism, may be well conserved among diverse taxa and environments, and that the intrinsic sensitivity of respiration to temperature is not influenced by ambient environmental temperature.     

It is optimal to be optimistic about survival

We investigate the optimal behaviour of an organism that is unable to obtain a reliable estimate of its mortality risk. In this case, natural selection will shape behaviour to be approximately optimal given the probability distribution of mortality risks in possible environments that the organism and its ancestors encountered. The mean of this distribution is the average mortality risk experienced by a randomly selected member of the species. We show that if an organism does not know the exact mortality risk, it should act as if the risk is less than the mean risk. This can be viewed as being optimistic. We argue that this effect is likely to be general.     

The role of inositol 1,4,5-trisphosphate 5-phosphatase in inositol signaling in the CNS of larval Manduca sexta

Production of inositol 1,4,5-trisphosphate (IP3) in cells results in the mobilization of intracellular calcium. Therefore, the dynamics of IP3 metabolism is important for calcium dependent processes in cells. This report investigates the coupling of mAChRs to the inositol lipid pathway in the CNS of the larval Manduca sexta. Stimulation of intact abdominal ganglia prelabeled with [3H]-inositol using a muscarinic agonist, oxotremorine-M (oxo-M), increased total inositol phosphate levels in a dose dependent manner (EC50 = 4.23 microM). These inositol phosphates consisted primarily of inositol 1,4-bisphosphate (IP2) and inositol monophosphate (IP1). Similarly, when nerve cord homogenates were provided with [3H]-phosphatidylinositol 4,5-bisphosphate ([3H]-PIP2) (10-13 microM) the predominant products were IP2 and IP1. In contrast, incubation of purified membranes with 1 mM oxo-M in the presence of 100 microM GTP gamma S and [3H]-PIP2 increased IP3 levels, suggesting that the direct activation of phospholipase C (PLC) by mAChRs occurs in a membrane delimited process. Together, these results suggest that in the intact nerve cord and in crude homogenates, a cytosolic 5-phosphatase quickly metabolizes IP3 to produce to IP2 and IP1. This enzyme was kinetically characterized using IP3 (Km = 43.7 microM, Vmax = 864 pmoles/min/mg) and IP4 (Km = 0.93 microM; Vmax = 300pmoles/min/mg) as substrates. The enzyme activity can be potently inhibited by two IP thiol compounds; IP3S3 (1,4,6) and IP3S3 (2,3,5), that show complex binding kinetics (Hill numbers < 1) and can distinguish different forms of the 5-phosphatase in purified membranes. These two inhibitors could be very useful tools to determine the role of the inositol lipid pathway in neuroexcitability.     

Mammalian choices: combining fast-but-inaccurate and slow-but-accurate decision-making systems

Empirical findings suggest that the mammalian brain has two decision-making systems that act at different speeds. We represent the faster system using standard signal detection theory. We represent the slower (but more accurate) cortical system as the integration of sensory evidence over time until a certain level of confidence is reached. We then consider how two such systems should be combined optimally for a range of information linkage mechanisms. We conclude with some performance predictions that will hold if our representation is realistic.     

Purification and Properties of NADH-Dependent 5,10-Methylenetetrahydrofolate Reductase (MetF) from Escherichia coli

A K-12 strain of Escherichia coli that overproduces methylenetetrahydrofolate reductase (MetF) has been constructed, and the enzyme has been purified to apparent homogeneity. A plasmid specifying MetF with six histidine residues added to the C terminus has been used to purify histidine-tagged MetF to homogeneity in a single step by affinity chromatography on nickel-agarose, yielding a preparation with specific activity comparable to that of the unmodified enzyme. The native protein comprises four identical 33-kDa subunits, each of which contains a molecule of noncovalently bound flavin adenine dinucleotide (FAD). No additional cofactors or metals have been detected. The purified enzyme catalyzes the reduction of methylenetetrahydrofolate to methyltetrahydrofolate, using NADH as the reductant. Kinetic parameters have been determined at 15°C and pH 7.2 in a stopped-flow spectrophotometer; the K_m for NADH is 13 μM, the K_m for CH₂-H₄folate is 0.8 μM, and the turnover number under V_max conditions estimated for the reaction is 1,800 mol of NADH oxidized min⁻¹ (mol of enzyme-bound FAD)⁻¹. NADPH also serves as a reductant, but exhibits a much higher K_m. MetF also catalyzes the oxidation of methyltetrahydrofolate to methylenetetrahydrofolate in the presence of menadione, which serves as an electron acceptor. The properties of MetF from E. coli differ from those of the ferredoxin-dependent methylenetetrahydrofolate reductase isolated from the homoacetogen Clostridium formicoaceticum and more closely resemble those of the NADH-dependent enzyme from Peptostreptococcus productus and the NADPH-dependent enzymes from eukaryotes.