Mössbauer spectroscopy on respiratory complex I: the iron-sulfur cluster ensemble in the NADH-reduced enzyme is partially oxidized

In mitochondria, complex I (NADH:quinone oxidoreductase) couples electron transfer to proton translocation across an energy-transducing membrane. It contains a flavin mononucleotide to oxidize NADH, and an unusually long series of iron-sulfur (FeS) clusters that transfer the electrons to quinone. Understanding electron transfer in complex I requires spectroscopic and structural data to be combined to reveal the properties of individual clusters and of the ensemble. EPR studies on complex I from Bos taurus have established that five clusters (positions 1, 2, 3, 5, and 7 along the seven-cluster chain extending from the flavin) are (at least partially) reduced by NADH. The other three clusters, positions 4 and 6 plus a cluster on the other side of the flavin, are not observed in EPR spectra from the NADH-reduced enzyme: they may remain oxidized, have unusual or coupled spin states, or their EPR signals may be too fast relaxing. Here, we use M?ssbauer spectroscopy on (57)Fe-labeled complex I from the mitochondria of Yarrowia lipolytica to show that the cluster ensemble is only partially reduced in the NADH-reduced enzyme. The three EPR-silent clusters are oxidized, and only the terminal 4Fe cluster (position 7) is fully reduced. Together with the EPR analyses, our results reveal an alternating profile of higher and lower potential clusters between the two active sites in complex I; they are not consistent with the consensus picture of a set of isopotential clusters. The implications for intramolecular electron transfer along the extended chain of cofactors in complex I are discussed.     

Attraction of Drosophila melanogaster males to food-related and fly odours

The fruit fly Drosophila melanogaster has become a model for olfaction and odour-mediated behaviour. In the wild, Drosophila flies aggregate on decaying fruit where they mate and oviposit and a strategy to find mates would be to locate fruit which has already been colonized by other flies. We therefore developed a bioassay to investigate attraction of males to food and fly odours. We showed that upwind flights are initiated by food odours. At shorter distances, males are attracted by volatiles produced by conspecifics. However, only odours produced by copulating flies attract males. This suggests either a synergistic effect of both male and female odours or changes in pheromone release during mating, that indicate the presence of sexually receptive females. Our findings demonstrate the essential role of food odours and pheromones for mate location in D. melanogaster.     

Path integration controls nest-plume following in desert ants

The desert ant Cataglyphis fortis is equipped with sophisticated navigational skills for returning to its nest after foraging. The ant's primary means for long-distance navigation is path integration, which provides a continuous readout of the ant's approximate distance and direction from the nest. The nest is pinpointed with the aid of visual and olfactory landmarks. Similar landmark cues help ants locate familiar food sites. Ants on their outward trip will position themselves so that they can move upwind using odor cues to find food. Here we show that homing ants also move upwind along nest-derived odor plumes to approach their nest. The ants only respond to odor plumes if the state of their path integrator tells them that they are near the nest. This influence of path integration is important because we could experimentally provoke ants to follow odor plumes from a foreign, conspecific nest and enter that nest. We identified CO(2) as one nest-plume component that can by itself induce plume following in homing ants. Taken together, the results suggest that path-integration information enables ants to avoid entering the wrong nest, where they would inevitably be killed by resident ants.     

The trypanosomatid-specific N terminus of RPA2 is required for RNA polymerase I assembly, localization, and function

African trypanosomes are the only organisms known to use RNA polymerase I (pol I) to transcribe protein-coding genes. These genes include VSG, which is essential for immune evasion and is transcribed from an extranucleolar expression site body (ESB). Several trypanosome pol I subunits vary compared to their homologues elsewhere, and the question arises as to how these variations relate to pol I function. A clear example is the N-terminal extension found on the second-largest subunit of pol I, RPA2. Here, we identify an essential role for this region. RPA2 truncation leads to nuclear exclusion and a growth defect which phenocopies single-allele knockout. The N terminus is not a general nuclear localization signal (NLS), however, and it fails to accumulate unrelated proteins in the nucleus. An ectopic NLS is sufficient to reinstate nuclear localization of truncated RPA2, but it does not restore function. Moreover, NLS-tagged, truncated RPA2 has a different subnuclear distribution to full-length protein and is unable to build stable pol I complexes. We conclude that the RPA2 N-terminal extension does not have a role exclusive to the expression of protein-coding genes, but it is essential for all pol I functions in trypanosomes because it directs trypanosomatid-specific interactions with RPA1.     

Discrimination training with multimodal stimuli changes activity in the mushroom body of the hawkmoth Manduca sexta

Background

The mushroom bodies of the insect brain play an important role in olfactory processing, associative learning and memory. The mushroom bodies show odor-specific spatial patterns of activity and are also influenced by visual stimuli.

Methodology/Principal Findings

Functional imaging was used to investigate changes in the in vivo responses of the mushroom body of the hawkmoth Manduca sexta during multimodal discrimination training. A visual and an odour stimulus were presented either together or individually. Initially, mushroom body activation patterns were identical to the odour stimulus and the multimodal stimulus. After training, however, the mushroom body response to the rewarded multimodal stimulus was significantly lower than the response to the unrewarded unimodal odour stimulus, indicating that the coding of the stimuli had changed as a result of training. The opposite pattern was seen when only the unimodal odour stimulus was rewarded. In this case, the mushroom body was more strongly activated by the multimodal stimuli after training. When no stimuli were rewarded, the mushroom body activity decreased for both the multimodal and unimodal odour stimuli. There was no measurable response to the unimodal visual stimulus in any of the experiments. These results can be explained using a connectionist model where the mushroom body is assumed to be excited by olfactory stimulus components, and suppressed by multimodal configurations.

Conclusions

Discrimination training with multimodal stimuli consisting of visual and odour cues leads to stimulus specific changes in the in vivo responses of the mushroom body of the hawkmoth.