Naris occlusion alters transductory protein immunoreactivity in olfactory epithelium

We have recently shown that unilateral naris occlusion (UNO) causes an increase in olfactory marker protein (OMP) immunoreactivity (IR) in mouse olfactory sensory neurons (OSN) from the occluded side of the nasal cavity and a decrease in OMP-IR on the non-occluded side, relative to controls. Given OMP's demonstrated role in olfactory modulation, these OMP-IR changes have been interpreted as a compensatory response by OSNs to odor deprivation on the occluded side and to supernormal exposure to odor on the non-occluded side of the nasal cavity. In the current study, we examined the developmental timing and the regional distribution of this process throughout the nasal cavity using immunocytochemistry. Results demonstrate that OMP-IR diverges in OSNs from the occluded side relative to the non-occluded side of the nasal cavity within eleven days after UNO, with statistically significant differences measurable after 17 days (n=16). We also measured relative levels of the Type 4 phosphodiesterase (PDE4A), another potential olfactory modulator, in nasal cavity tissue from UNO (n=8) and untreated mice (n=9) using western blots and immunocytochemistry. Like OMP, PDE4A-IR increased on the occluded side of the nasal cavity after UNO. Finally, we used immunocytochemistry to assess relative levels of olfactory-specific adenylyl cyclase (ACIII, n=4) and G-protein (Golf, n=2) in OSNs from the occluded and non-occluded sides of the nasal cavity of UNO mice. Following UNO, ACIII but not Golf -IR levels diverged comparing the occluded to the non-occluded sides of the nasal cavity. Taken together, our findings provide support for the previously unknown phenomenon of compensatory responses by OSNs to odor environment.     

Directed evolution of microbial oxidative enzymes

In the past year, a number of oxidative enzymes have been the target of directed evolution. Catalase reaction specificity has been shifted to peroxidase, the high pH, thermal and oxidative stability of a fungal peroxidase has been dramatically improved, and the substrate specificity of cytochrome P450 has been altered to include substrates that the wild-type enzymes are incapable of oxidizing.     

Mechanisms of ventricular arrhythmias: a dynamical systems-based perspective

Defining the cellular electrophysiological mechanisms for ventricular tachyarrhythmias is difficult, given the wide array of potential mechanisms, ranging from abnormal automaticity to various types of reentry and kk activity. The degree of difficulty is increased further by the fact that any particular mechanism may be influenced by the evolving ionic and anatomic environments associated with many forms of heart disease. Consequently, static measures of a single electrophysiological characteristic are unlikely to be useful in establishing mechanisms. Rather, the dynamics of the electrophysiological triggers and substrates that predispose to arrhythmia development need to be considered. Moreover, the dynamics need to be considered in the context of a system, one that displays certain predictable behaviors, but also one that may contain seemingly stochastic elements. It also is essential to recognize that even the predictable behaviors of this complex nonlinear system are subject to small changes in the state of the system at any given time. Here we briefly review some of the short-, medium-, and long-term alterations of the electrophysiological substrate that accompany myocardial disease and their potential impact on the initiation and maintenance of ventricular arrhythmias. We also provide examples of cases in which small changes in the electrophysiological substrate can result in rather large differences in arrhythmia outcome. These results suggest that an interrogation of cardiac electrical dynamics is required to provide a meaningful assessment of the immediate risk for arrhythmia development and for evaluating the effects of putative antiarrhythmic interventions.     

Predicted warming and browning affect timing and magnitude of plankton phenological events in lakes: a mesocosm study

1. Aquatic ecosystems in Northern Europe are expected to face increases in temperature and water colour (TB) in future. While effects of these factors have been studied separately, it is unknown whether and how a combination of them might affect phenological events and trophic interactions. 2. In a mesocosm study, we combined both factors to create conditions expected to arise during the coming century. We focused on quantifying effects on timing and magnitude of plankton spring phenological events and identifying possible mismatches between resources (phytoplankton) and consumers (zooplankton). 3. We found that the increases in TB had important effects on timing and abundance of different plankton groups. While increased temperature led to an earlier peak in phytoplankton and zooplankton and a change in the relative timing of different zooplankton groups, increased water colour reduced chlorophyll‐a concentrations. 4. Increased TB together benefitted cladocerans and calanoid copepods and led to stronger top‐down control of algae by zooplankton. There was no sign of a mismatch between primary producers and grazers as reported from other studies. 5. Our results point towards an earlier onset of plankton spring growth in shallow lakes in future with a stronger top‐down control of phytoplankton by zooplankton grazers.     

Effects of brown and turbid water on piscivore–prey fish interactions along a visibility gradient

1. Environmental changes such as eutrophication and increasing inputs of humic matter (brownification) may have strong effects on predator–prey interactions in lakes through a reduction in the visual conditions affecting foraging behaviour of visually oriented predators. 2. In this experiment, we studied the effects of visual range (25–200 cm) in combination with optically deteriorating treatments (algae, clay or brown humic water) on predator–prey interactions between pike (Esox lucius) and roach (Rutilus rutilus). We measured effects on reaction distance and strike distance for pike and escape distance for roach, when pike individuals were exposed to free‐swimming roach as well as to roach held in a glass cylinder. 3. We found that reaction distance decreased with decreasing visual range caused by increasing levels of algae, clay or humic matter. The effect of reaction distance was stronger in turbid water (clay, algae) than in the brown water treatment. 4. Strike distance was neither affected by visual range nor by optical treatment, but we found shorter strike distances when pike attacked roach using visual cues only (roach held in a cylinder) compared to when pike could use multiple senses (free‐swimming roach). Escape distance for roach was longer in turbid than in brown water treatments. 5. Changes in environmental drivers, such as eutrophication and brownification, affecting the optical climate should thus have consequences for the strength of predator–prey interactions through changes in piscivore foraging efficiency and prey escape behaviour. This in turn may affect lake ecosystems through higher‐order interactions.     

Similarities of Drosophila rab GTPases Based on Expression Profiling: Completion and Analysis of the rab-Gal4 Kit

We recently generated rab-Gal4 lines for 25 of 29 predicted Drosophila rab GTPases. These lines provide tools for the expression of reporters, mutant rab variants or other genes, under control of the regulatory elements of individual rab loci. Here, we report the generation and characterization of the remaining four rab-Gal4 lines. Based on the completed 'rab-Gal4 kit' we performed a comparative analysis of the cellular and subcellular expression of all rab GTPases. This analysis includes the cellular expression patterns in characterized neuronal and non-neuronal cells and tissues, the subcellular localization of wild type, constitutively active and dominant negative rab GTPases and colocalization with known intracellular compartment markers. Our comparative analysis identifies all Rab GTPases that are expressed in the same cells and localize to the same intracellular compartments. Remarkably, similarities based on these criteria are typically not predicted by primary sequence homology. Hence, our findings provide an alternative basis to assess potential roles and redundancies based on expression in developing and adult cell types, compartment identity and subcellular localization.     

AMP-Activated Kinase Restricts Rift Valley Fever Virus Infection by Inhibiting Fatty Acid Synthesis

The cell intrinsic innate immune responses provide a first line of defense against viral infection, and often function by targeting cellular pathways usurped by the virus during infection. In particular, many viruses manipulate cellular lipids to form complex structures required for viral replication, many of which are dependent on de novo fatty acid synthesis. We found that the energy regulator AMPK, which potently inhibits fatty acid synthesis, restricts infection of the Bunyavirus, Rift Valley Fever Virus (RVFV), an important re-emerging arthropod-borne human pathogen for which there are no effective vaccines or therapeutics. We show restriction of RVFV both by AMPK and its upstream activator LKB1, indicating an antiviral role for this signaling pathway. Furthermore, we found that AMPK is activated during RVFV infection, leading to the phosphorylation and inhibition of acetyl-CoA carboxylase, the first rate-limiting enzyme in fatty acid synthesis. Activating AMPK pharmacologically both restricted infection and reduced lipid levels. This restriction could be bypassed by treatment with the fatty acid palmitate, demonstrating that AMPK restricts RVFV infection through its inhibition of fatty acid biosynthesis. Lastly, we found that this pathway plays a broad role in antiviral defense since additional viruses from disparate families were also restricted by AMPK and LKB1. Therefore, AMPK is an important component of the cell intrinsic immune response that restricts infection through a novel mechanism involving the inhibition of fatty acid metabolism.