Vladimiros Thoma

Food intake is regulated by internal state. This function is mediated by hormones and neuropeptides, which are best characterized in popular model species. However, the evolutionary origins of such feeding-regulating neuropeptides are poorly understood. We used the jellyfishCladonemato address this question. Our combined transcriptomic, behavioral, and anatomical approaches identified GLWamide as a feeding-suppressing peptide that selectively inhibits tentacle contraction in this jellyfish. In the fruit flyDrosophila, myoinhibitory peptide (MIP) is a related satiety peptide. Surprisingly, we found that GLWamide and MIP were fully interchangeable in these evolutionarily distant species for feeding suppression. Our results suggest that the satiety signaling systems of diverse animals share an ancient origin.

To survive, all animals must find, inspect, and ingest food. Behavioral coordination and control of feeding is therefore a challenge that animals must face. Here, we focus on how the gustatory system guides the precise execution of behavioral sequences that promote ingestion and suppresses competing behaviors. We summarize principles learnt fromDrosophila, where underlying sensory neuronal mechanisms are illustrated in great detail. Moreover, we compare these principles with findings in other animals, where such coordination plays prominent roles. These examples suggest that the use of gustatory information for feeding coordination has an ancient origin and is prevalent throughout the animal kingdom.

Finding food sources is essential for survival. Insects detect nutrients with external taste receptor neurons. Drosophila possesses multiple taste organs that are distributed throughout its body. However, the role of different taste organs in feeding remains poorly understood. By blocking subsets of sweet taste receptor neurons, we show that receptor neurons in the legs are required for immediate sugar choice. Furthermore, we identify two anatomically distinct classes of sweet taste receptor neurons in the leg. The axonal projections of one class terminate in the thoracic ganglia, whereas the other projects directly to the brain. These two classes are functionally distinct: the brain-projecting neurons are involved in feeding initiation, whereas the thoracic ganglia-projecting neurons play a role in sugar-dependent suppression of locomotion. Distinct receptor neurons for the same taste quality may coordinate early appetitive responses, taking advantage of the legs as the first appendages to contact food.

Aversive olfactory memory is formed in the mushroom bodies in Drosophila melanogaster. Memory retrieval requires mushroom body output, but the manner in which a memory trace in the mushroom body drives conditioned avoidance of a learned odor remains unknown. To identify neurons that are involved in olfactory memory retrieval, we performed an anatomical and functional screen of defined sets of mushroom body output neurons. We found that MB-V2 neurons were essential for retrieval of both short- and long-lasting memory, but not for memory formation or memory consolidation. MB-V2 neurons are cholinergic efferent neurons that project from the mushroom body vertical lobes to the middle superiormedial protocerebrum and the lateral horn. Notably, the odor response of MB-V2 neurons was modified after conditioning. As the lateral horn has been implicated in innate responses to repellent odorants, we propose that MB-V2 neurons recruit the olfactory pathway involved in innate odor avoidance during memory retrieval.

The reaction between chromium(III) and 2,3‐dihydroxybenzoic acid (2,3‐DHBA) takes place in at least three stages, involving various intermediates. The ligand (2,3‐DHBA)‐to‐chromium(III) ratio in the final product of the reaction is 1 : 1. The first stage is suggested to be the reaction of with the ligand in weak acidic aqueous solutions that follows an I_d mechanism. The second and third stages do not depend on the concentrations of chromium(III), and their activation parameters are ΔH^≠ _2(obs) = 61.2 ± 3.1 kJmol⁻¹, ΔS^≠ _2(obs) = −91.1 ± 11.0 JK⁻¹mol⁻¹, ΔH^≠ _3(obs) = 124.5 ± 8.7 kJmol⁻¹, and ΔS^≠ _3(obs) = 95.1 ± 29.0 JK⁻¹mol⁻¹. These two stages are proposed to proceed via associative mechanisms. The positive value of ΔS^≠ _3(obs) can be explained by the opening of a four‐membered ring (positive entropy change) and the breaking of a hydrogen bond (positive entropy change) at the associative step of the replacement of the carboxyl group by the hydroxyl group at the chromium(III) center (negative entropy change in associative mechanisms). The reactions are accompanied by proton release, as shown by the pH decrease.

The crystal structures of the C57A and V13G molecular variants of Allochromatium vinosum 2[4Fe–4S] ferredoxin (AlvinFd) and that of the homologous ferredoxin from Escherichia coli (EcFd) have been determined at 1.05-, 1.48-, and 1.65-Å resolution, respectively. The present structures combined with cyclic voltammetry studies establish clear effects of the degree of exposure of the cluster with the lowest reduction potential (cluster I) towards less negative reduction potentials (E°). This is better illustrated by V13G AlvinFd (high exposure, E° = −594 mV) and EcFd (low exposure, E° = −675 mV). In C57A AlvinFd, the movement of the protein backbone, as a result of replacing the noncoordinating Cys57 by Ala, leads to a +50-mV upshift of the potential of the nearby cluster I, by removal of polar interactions involving the thiolate group and adjustment of the hydrogen-bond network involving the cluster atoms. In addition, the present structures and other previously reported accurate structures of this family of ferredoxins indicate that polar interactions of side chains and water molecules with cluster II sulfur atoms, which are absent in the environment of cluster I, are correlated to the approximately 180–250 mV difference between the reduction potentials of clusters I and II. These findings provide insight into the significant effects of subtle structural differences of the protein and solvent environment around the clusters of [4Fe–4S] ferredoxins on their electrochemical properties.