Multiphasic On/Off Pheromone Signalling in Moths as Neural Correlates of a Search Strategy

Insects and robots searching for odour sources in turbulent plumes face the same problem: the random nature of mixing causes fluctuations and intermittency in perception. Pheromone-tracking male moths appear to deal with discontinuous flows of information by surging upwind, upon sensing a pheromone patch, and casting crosswind, upon losing the plume. Using a combination of neurophysiological recordings, computational modelling and experiments with a cyborg, we propose a neuronal mechanism that promotes a behavioural switch between surge and casting. We show how multiphasic On/Off pheromone-sensitive neurons may guide action selection based on signalling presence or loss of the pheromone. A Hodgkin-Huxley-type neuron model with a small-conductance calcium-activated potassium (SK) channel reproduces physiological On/Off responses. Using this model as a command neuron and the antennae of tethered moths as pheromone sensors, we demonstrate the efficiency of multiphasic patterning in driving a robotic searcher toward the source. Taken together, our results suggest that multiphasic On/Off responses may mediate olfactory navigation and that SK channels may account for these responses.     

Voltage-dependent channel formation by rods of helical polypeptides

Summary The voltage-dependence of channel formation by alamethicin and its natural analogues can be described by a dipole flip-flop gating model, based on electric field-induced transbilayer orientational movements of single molecules. These field-induced changes in orientation result from the large permanent dipole moment of alamethicin, which adopts -helical conformation in hydrophobic medium. It was, therefore, supposed that the only structural requirement for voltage-dependent formation of alamethicin-type channels might be a rigid lipophilic helical segment of minimum length.In order to test this hypothesis we synthesized a family of lipophilic polypeptides—Boc-(Ala-Aib-Ala-Aib-Ala) _n -OMe,n=1–4—which adopt -helical conformation forn=2–4 and studied their interaction with planar lipid bilayers. Surprisingly, despite their large difference in chain length, all four polypeptides showed qualitatively similar behavior. At low field strength of the membrane electric field these polypeptides induce a significant, almost voltage-independent increase of the bilayer conductivity. At high field strength, however, a strongly voltage-dependent conductance increase occurs similar to that observed with alamethicin. It results from the opening of a multitude of ion translocating channels within the membrane phase.The steady-state voltage-dependent conductance depends on the 8^th–9^th power of polypeptide concentration and involves the transfer of 4–5 formal elementary charges. From the power dependences on polypeptide concentration and applied voltage of the time constants in voltage-jump current-relaxation experiments, it is concluded that channels could be formed from preexisting dodecamer aggregates by the simultaneous reorientation of six formal elementary charges. Channels exhibit large conductance values of several nS, which become larger towards shorter polypeptide chain length. A mean channel diameter of 19 Å is estimated corresponding roughly to the lumen diameter of a barrel comprised of 10 -helical staves. Similar to experiments with the N-terminal Boc-derivative of alamethicin we did not observe the burst sequence of nonintegral conductance steps typical of natural (N-terminal Ac-Aib)-alamethicin. Saturation in current/voltage curves as well as current inactivation in voltage-jump current-relaxation experiments are found. This may be understood by assuming that channels are generated as dodecamers but, while reaching the steady state, reduce their size to that of an octamer or nonamer. We conclude that the overall behavior of these synthetic polypeptides is very similar to that of alamethicin. They exhibit the same concentration and voltage-dependences but lack the stabilizing principle of resolved channel states characteristic of alamethicin.     

Localization of sequences regulating ancestral and acquired sites of esterase6 activity in Drosophila melanogaster

We have broadly defined the DNA regions regulating esterase6 activity in several life stages and tissue types of D. melanogaster using P- element-mediated transformation of constructs that contain the esterase6 coding region and deletions or substitutions in 5' or 3' flanking DNA. Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and the primary sequences regulating its activity lie between -171 and -25 bp relative to the translation initiation site: deletion of these sequences decrease activity approximately 20-fold. Hemolymph activity is also modulated by four other DNA regions, three of which lie 5' and one of which lies 3' of the coding region. Of these, two have positive and two have negative effects, each of approximately twofold. Esterase6 activity is present also in two male reproductive tract tissues; the ejaculatory bulb, which is another ancestral activity site, and the ejaculatory duct, which is a recently acquired site within the melanogaster species subgroup. Activities in these tissues are at least in part independently regulated: activity in the ejaculatory bulb is conferred by sequences between -273 and -172 bp (threefold decrease when deleted), while activity in the ejaculatory duct is conferred by more distal sequences between -844 and -614 bp (fourfold decrease when deleted). The reproductive tract activity is further modulated by two additional DNA regions, one in 5' DNA (-613 to -284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to +2731 bp; threefold decrease when deleted) that probably overlaps the adjacent esteraseP gene. Collating these data with previous studies suggests that expression of EST6 in the ancestral sites is mainly regulated by conserved proximal sequences while more variable distal sequences regulate expression in the acquired ejaculatory duct site.      

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

Autoradiographic localizatio of [125I]-C-ANP compared to [125I]-ANP in rat tissue

Summary Whole-body autoradiography demonstrated the different distribution of [¹²⁵I]-C-ANP and [¹²⁵I]-ANP to rat tissues. Highest enrichment of radioactivity of both labelled peptides was found in the kidney. In some organs we found remarkable differences between [¹²⁵I]-ANP and [¹²⁵I]-C-ANP. In the kidney cortex, especially in the glomeruli, as well as in the endocardium, the zona glomerulosa and the medulla of the adrenal gland, where high levels of radioactivity after [¹²⁵I]-ANP administration were detected, no or just few radioactivity was found after administration of [¹²⁵I]-C-ANP. On the other hand in the kidney papilla and the outer subcortical medulla, characteristic blackening was found after [¹²⁵I]-C-ANP administration. Those differences might be important for the understanding of pharmacological actions of ANP analogues.This work is part of the doctoral thesis of Frank Heidemann to be presented at the Ludwig-Maximilians-Universität München, FRG     

The role of snail aestivation in transmission of schistosomiasis in changing climatic conditions

Schistosomiasis vector snails are subjected to extreme seasonal changes, particularly in ephemeral rivers and lentic waterbodies. In the tropics, aestivation is one of the adaptive strategies for survival and is used by snails in times of extremely high temperatures and desiccation. Aestivation therefore plays an important role in maintaining the transmission of schistosomiasis. This review assesses the possible impacts of climate change on the temporal and spatial distribution of schistosomiasis-transmitting snails with special emphasis on aestivation, and discusses the effect of schistosome infection on aestivation ability. The impacts of parasite development on snails, as well as physiological changes, are discussed with reference to schistosomiasis transmission. This review shows that schistosome-infected snails have lower survival rates during aestivation, and that those that survive manage to get rid of the infection. In general, snail aestivation ability is poor and survival chances diminish with time. Longer dry periods result in fewer, as well as uninfected, snails. However, the ability of the surviving snails to repopulate the habitats is high.     

Attenuation of pattern recognition receptor signaling is mediated by a MAP kinase kinase kinase

Pattern recognition receptors (PRRs) play a key role in plant and animal innate immunity. PRR binding of their cognate ligand triggers a signaling network and activates an immune response. Activation of PRR signaling must be controlled prior to ligand binding to prevent spurious signaling and immune activation. Flagellin perception in Arabidopsis through FLAGELLIN‐SENSITIVE 2 (FLS2) induces the activation of mitogen‐activated protein kinases (MAPKs) and immunity. However, the precise molecular mechanism that connects activated FLS2 to downstream MAPK cascades remains unknown. Here, we report the identification of a differentially phosphorylated MAP kinase kinase kinase that also interacts with FLS2. Using targeted proteomics and functional analysis, we show that MKKK7 negatively regulates flagellin‐triggered signaling and basal immunity and this requires phosphorylation of MKKK7 on specific serine residues. MKKK7 attenuates MPK6 activity and defense gene expression. Moreover, MKKK7 suppresses the reactive oxygen species burst downstream of FLS2, suggesting that MKKK7‐mediated attenuation of FLS2 signaling occurs through direct modulation of the FLS2 complex.     

Untersuchungen über die Osteon- und Lamellenformen im Extremitätenskelet des Erwachsenen

Zusammenfassung Auf Grund der Untersuchung von Knochenquerschnitten eines gesunden 43jährigen Mannes, bestätigt durch noch zu veröffentlichende Untersuchungen an Tibien verschiedener Individuen, werden die Strukturformen des Knochens nach ihrem Querschnittsbild beschrieben.Es wird zwischen Osteonen und Tangentiallamellen unterschieden. Zu den Tangentiallamellen mit dem mehr oder minder parallelen Verlauf zur Knochenoberfläche gehören die bisher als Generallamellen und Schaltlamellen beschriebenen Systeme.Soweit eine Lamellengliederung vorhanden ist, zeichnen sich die Tangentiallamellen durch den strengen Wechsel zwischen flach und steil gewickelten aus.Auf Grund des Querschnittsbildes werden verschiedene Osteonformen unterschieden. Die Größe des einzelnen Osteonquerschnittes wird mit Hilfe der Lamellenzahl bestimmt. Gleichzeitig wird die Steigungsfolge beachtet, d. h. der Wechsel des Kollagenfaserverlaufs von Lamelle zu Lamelle.Es ergibt sich, daß die kleineren Osteone überwiegend in der peripheren Schnitthälfte, die größeren dagegen in der zentralen liegen. Der regelmäßige Wechsel der Steigungsfolge nimmt von den kleineren zu den größeren Osteonen hin ab, die mehr steile Verlaufsweise dagegen zu. Die kleineren Größenklassen lassen häufiger die lamelläre Gliederung vermissen als die großen.Abschließend wird erörtert, daß sowohl das Osteon wie die Lamelle nur als eine besondere Lagerungsform der Kollagenfasern im Knochen angesehen werden können. Der Begriff Osteon wurde in Anlehnung an die Begriffe der überwiegend zellulären Einheiten Neuron und Chondron bzw. der sog. Entwicklungs- und Funktionseinheit Nephron gebildet. Die zirkuläre Lagerung der Kollagenfasern hat aller Voraussicht nach eine besondere festigkeitstheoretische Bedeutung. Sie ist aber abhängig vom Gefäßbaum, an dessen Verzweigungen Doppelbildungen auftreten. Diese Doppelbildungen teilen sich und begleiten die Gefäßäste. Sie werden damit zum Osteon, das sich nach Querschnittsgröße und Wicklung in benachbarten Querschnitten verschieden verhalten kann. Die zirkuläre Wicklung führt nicht zu individuellen Gebilden, die den Knochen wie Bausteine aufbauen. Sie stellt ein System dar, das den Gefäßbaum im Knochen in mehr oder minder kontinuierlichem Zusammenhang begleitet. Die zirkulären Wicklungen gehen ohne Abgrenzung in die übrigen Lamellensysteme, die Tangentiallamellen, über. Osteone und Tangentiallamellen erscheinen damit als eine übergeordnete Lagerungsform der Kollagenfasern. Die nächstniedere Stufe der Lagerung ist die Lamelle.Mit Unterstützung der Deutschen Forschungsgemeinschaft.     

1-Thio-beta-D-galactofuranosides: synthesis and evaluation as beta-D- galactofuranosidase inhibitors

Beta-D-galactofuranosidase is a good chemotherapeutic target for the design of inhibitors, since beta-D-galactofuranose is a constituent of important parasite glycoconjugates but is not present in the host mammals. With this aim, we have synthesized for the first time alkyl, benzyl and aryl 1-thio-beta-D-galactofuranosides by condensation of penta-O-benzoyl-alpha,beta-D-galactofuranose with the corresponding thiols, in the presence of SnCl4as catalyst. The complete chemical and spectroscopical characterization of these compounds showed that the reaction was stereoselective. Debenzoylation with sodium methoxide afforded the beta-S-galactofuranosides in high yield. The thioglycosides were tested as inhibitors of the beta-D- galactofuranosidase of Penicillium fellutanum, using for the first time 4-nitrophenyl-beta-D-galactofuranoside as chromogenic substrate. The 4- aminophenyl-1-thio-beta-D-galactofuranoside, obtained by catalytic hydrogenation of the nitrophenyl derivative, was the best inhibitor being then an adequate ligand for the preparation of an affinity phase aimed at the isolation of beta-d-galactofuranosidases from different sources. Also the inhibitory activity of d-galactono-1, 4-lactone was shown.