A Toll-receptor map underlies structural brain plasticity

Experience alters brain structure, but the underlying mechanism remained unknown. Structural plasticity reveals that brain function is encoded in generative changes to cells that compete with destructive processes driving neurodegeneration. At an adult critical period, experience increases fiber number and brain size in Drosophila. Here, we asked if Toll receptors are involved. Tolls demarcate a map of brain anatomical domains. Focusing on Toll-2, loss of function caused apoptosis, neurite atrophy and impaired behaviour. Toll-2 gain of function and neuronal activity at the critical period increased cell number. Toll-2 induced cycling of adult progenitor cells via a novel pathway, that antagonized MyD88-dependent quiescence, and engaged Weckle and Yorkie downstream. Constant knock-down of multiple Tolls synergistically reduced brain size. Conditional over-expression of Toll-2 and wek at the adult critical period increased brain size. Through their topographic distribution, Toll receptors regulate neuronal number and brain size, modulating structural plasticity in the adult brain.

Everything that you experience leaves its mark on your brain. When you learn something new, the neurons involved in the learning episode grow new projections and form new connections. Your brain may even produce new neurons. Physical exercise can induce similar changes, as can taking antidepressants. By contrast, stress, depression, ageing and disease can have the opposite effect, triggering neurons to break down and even die. The ability of the brain to change in response to experience is known as structural plasticity, and it is in a tug-of-war with processes that drive neurodegeneration.

Structural plasticity occurs in other species too: for example, it was described in the fruit fly more than a quarter of a century ago. Yet, the molecular mechanisms underlying structural plasticity remain unclear. Li et al. now show that, in fruit flies, this plasticity involves Toll receptors, a family of proteins present in the brain but best known for their role in the immune system.

Fruit flies have nine different Toll receptors, the most abundant being Toll-2. When activated, these proteins can trigger a series of molecular events in a cell. Li et al. show that increasing the amount of Toll-2 in the fly brain makes the brain produce new neurons. Activating neurons in a brain region has the same effect, and this increase in neuron number also depends on Toll-2. By contrast, reducing the amount of Toll-2 causes neurons to lose their projections and connections, and to die, and impairs fly behaviour.

Li et al. also show that each Toll receptor has a unique distribution across the fly brain. Different types of experiences activate different brain regions, and therefore different Toll receptors. These go on to trigger a common molecular cascade, but they modulate it such as to result in distinct outcomes. By working together in different combinations, Toll receptors can promote either the death or survival of neurons, and they can also drive specific brain cells to remain dormant or to produce new neurons.

By revealing how experience changes the brain, Li et al. provide clues to the way neurons work and form; these findings may also help to find new treatments for disorders that change brain structure, such as certain psychiatric conditions. Toll-like receptors in humans could thus represent a promising new target for drug discovery.

Multi-stability with ambiguous visual stimuli in Drosophila orientation behavior

It is widely accepted for humans and higher animals that vision is an active process in which the organism interprets the stimulus. To find out whether this also holds for lower animals, we designed an ambiguous motion stimulus, which serves as something like a multi-stable perception paradigm in Drosophila behavior. Confronted with a uniform panoramic texture in a closed-loop situation in stationary flight, the flies adjust their yaw torque to stabilize their virtual self-rotation. To make the visual input ambiguous, we added a second texture. Both textures got a rotatory bias to move into opposite directions at a constant relative angular velocity. The results indicate that the fly now had three possible frames of reference for self-rotation: either of the two motion components as well as the integrated motion vector of the two. In this ambiguous stimulus situation, the flies generated a continuous sequence of behaviors, each one adjusted to one or another of the three references.

Vision is considered an active process in humans and higher animals in which the stimulus is interpreted by the subject and can be perceived in different ways if it is ambiguous. We aimed to find out whether this also holds for lower animals, such as the fruit fly Drosophila melanogaster. To provide ambiguity, we exposed flies to transparent motion stimuli in a flight simulator and found their behavior to be multi-stable. These results show that the visual system of the fly can separate the individual components of a transparent motion stimulus, and that this kind of stimulus is ambiguous to the fly. The extent to which the fly shows component selectivity in its behavior depends on several properties of the stimulus, like pattern contrast and element density. The alternations between the different behaviors exhibit a stochasticity reminiscent of the temporal dynamics in human multi-stable perception.

Starvation promotes odor/feeding-time associations in flies

Starvation causes a motivational state that facilitates diverse behaviors such as feeding, walking, and search. Starved Drosophila can form odor/feeding-time associations but the role of starvation in encoding of “time” is poorly understood. Here we show that the extent of starvation is correlated with the fly's ability to establish odor/feeding-time memories. Prolonged starvation promotes odor/feeding-time associations after just a single cycle of reciprocal training. We also show that starvation is required for acquisition but is dispensable for retrieval of odor/feeding-time memory. Finally, even with extended starvation, a functional circadian oscillator is indispensable for establishing odor/feeding-time memories.

Inescapable Stress Changes Walking Behavior in Flies - Learned Helplessness Revisited

Like other animals flies develop a state of learned helplessness in response to unescapable aversive events. To show this, two flies, one 'master', one 'yoked', are each confined to a dark, small chamber and exposed to the same sequence of mild electric shocks. Both receive these shocks when the master fly stops walking for more than a second. Behavior in the two animals is differently affected by the shocks. Yoked flies are transiently impaired in place learning and take longer than master flies to exit from the chamber towards light. After the treatment they walk more slowly and take fewer and shorter walking bouts. The low activity is attributed to the fly's experience that its escape response, an innate behavior to terminate the electric shocks, does not help anymore. Earlier studies using heat pulses instead of electric shocks had shown similar effects. This parallel supports the interpretation that it is the uncontrollability that induces the state.

Visual Attention in Flies-Dopamine in the Mushroom Bodies Mediates the After-Effect of Cueing

Visual environments may simultaneously comprise stimuli of different significance. Often such stimuli require incompatible responses. Selective visual attention allows an animal to respond exclusively to the stimuli at a certain location in the visual field. In the process of establishing its focus of attention the animal can be influenced by external cues. Here we characterize the behavioral properties and neural mechanism of cueing in the fly Drosophila melanogaster. A cue can be attractive, repulsive or ineffective depending upon (e.g.) its visual properties and location in the visual field. Dopamine signaling in the brain is required to maintain the effect of cueing once the cue has disappeared. Raising or lowering dopamine at the synapse abolishes this after-effect. Specifically, dopamine is necessary and sufficient in the αβ-lobes of the mushroom bodies. Evidence is provided for an involvement of the αβ_posterior Kenyon cells.

Flies remember the time of day

The circadian clock enables organisms to anticipate daily environmental cycles and drives corresponding changes in behavior [1, 2]. Such endogenous oscillators also enable animals to display time-specific memory [1, 3-5]. For instance, mice and honeybees associate the location of a stimulus (like food or mate) with a certain time of day (time-place learning) [6, 7]. However, the mechanism underlying time-related learning and memory is not known. In the present study, we investigate time-specific odor learning. We use a genetically tractable animal, the fly Drosophila melanogaster. Starved flies are trained in the morning and afternoon to associate distinct odors with sucrose reward. The training is repeated the next day, and their time-dependent odor preference is tested on the third day. Our results indicate that Drosophila can express appetitive memory at the relevant time of day if the two conditioning events are separated by more than 4 hr. Flies can form time-odor associations in constant darkness (DD) as well as in a daily light-dark (LD) cycle, but not when kept under constant light (LL) conditions. Circadian clock mutants, period(01) (per(01)) and clock(AR) (clk(AR)), learned to associate sucrose reward with a certain odor but were unable to form time-odor associations. Our findings show that flies can utilize temporal information as an additional cue in appetitive learning. Time-odor learning in flies depends on a per- and clk-dependent endogenous mechanism that is independent of environmental light cues.

Outcome learning, outcome expectations, and intentionality in Drosophila

An animal generates behavioral actions because of the effects of these actions in the future. Occasionally, the animal may generate an action in response to a certain event or situation. If the outcome of the action is adaptive, the animal may keep this stimulus–response link in its behavioral repertoire, in case the event or situation occurs again. If a responsive action is innate but the outcome happens to be less adaptive than it had been before, the link may be loosened. This adjustment of outcome expectations involves a particular kind of learning, which will be called “outcome learning.” The present article discusses several examples of outcome learning in Drosophila. Learning and memory are intensely studied in flies, but the focus is on classical conditioning. Outcome learning, a particular form of operant learning, is of special significance, because it modulates outcome expectations that are operational components of action selection and intentionality.

Central complex and mushroom bodies mediate novelty choice behavior in Drosophila

Novelty choice, a visual paired-comparison task, for the fly Drosophila melanogaster is studied with severely restrained single animals in a flight simulator. The virtual environment simulates free flight for rotation in the horizontal plane. The behavior has three functional components: visual azimuth orientation, working memory, and pattern discrimination (perception). Here we study novelty choice in relation to its neural substrate in the brain and show that it requires the central complex and, in particular, the ring neurons of the ellipsoid body. Surprisingly, it also involves the mushroom bodies which are needed specifically in the comparison of patterns of different sizes.

Störung des Nachweises der Ribonucleinsäure-Polymerase in Tabakblättern durch eine Nucleosidase

An enzymatic degradation of ATP, ADP, AMP to adenine was observed in tobacco leaves. This enzymatic activity was concentrated 130 fold. 14C-adenine can interfere with the determination of polymerase by adsorption to filters and bentonite. The degradation of ATP can be avoided by addition of phosphorenol pyruvate and kinase. A weak polymerase activity was found to be associated with particles in leaf extracts, but was not found in the supernatant.

'Humans and other animals'-on the scope of brain science

Abstract: This essay is dedicated to Obaid on the occasion of his 80th birthday. We both worked on the behavior of Drosophila and on what underlies behavior in the fly brain. Is that the fly's mind? The essay is about some limitations of brain science. It is just a little piece of writing. It is meant to honor Obaid for his contributions to Drosophila neurogenetics in 40 years and to science in India. I hope he takes it instead of a bowl of flowers-adding to the praise.

Photoreceptors and neural circuitry underlying phototaxis in insects

Visual behavior of insects has long been studied, but it is only recently that a wide variety of genetic tools has become available for its analysis. Perhaps the most basic visual behaviour is phototaxis, locomotion towards a source of light. It is known in many insects and has been studied for over a century but the neural network underlying it is little understood. We recently described in the fruit fly Drosophila how different photoreceptor types contribute to phototaxis. By blocking subsets of them we showed that at least four of the five types are involved. In this short review, we compare phototactic behaviour in fruit flies and other insects (especially honeybees), and discuss what is known about the underlying neural circuitry. :

Structural brain mutant of Drosophila melanogaster with reduced cell number in the medulla cortex and with normal optomotor yaw response

KS58, one out of six known alleles of the small optic lobes (sol) gene in Drosophila melanogaster, reduces the cell number in the medulla cortex by degeneration of ganglion cells in the pupae to about 50%. Also, about half the volume of the medulla and lobula complex neuropils is missing. Many Golgistained cells in the mutant optic lobes resemble their homologues in wild type. However, special classes of transmedullary columnar neurons projecting to the lobula or to both lobula and lobula plate are not seen in the mutant. Some neurons linking the lobula complex to the central brain send branches to the medulla (the branches do not exist in wild type); some other types seem to be missing. The fate mapping of the KS58 focus reveals a location ventral to the head bristles and in sine oculis (so) flies the mutation further reduces the rudiments of the optic lobes normally seen. Therefore the sol phenotype is not induced by mutant eyes and the primary gene action seems to be on nervous tissue. The structural alterations of the small optic lobes are reflected in visual orientation behavior. The optomotor yaw response, however, is almost quantitatively preserved. The respective neural network should still be present in the mutant optic lobes.

A high-level 3D visualization API for Java and ImageJ

Background

Current imaging methods such as Magnetic Resonance Imaging (MRI), Confocal microscopy, Electron Microscopy (EM) or Selective Plane Illumination Microscopy (SPIM) yield three-dimensional (3D) data sets in need of appropriate computational methods for their analysis. The reconstruction, segmentation and registration are best approached from the 3D representation of the data set.

Results

Here we present a platform-independent framework based on Java and Java 3D for accelerated rendering of biological images. Our framework is seamlessly integrated into ImageJ, a free image processing package with a vast collection of community-developed biological image analysis tools. Our framework enriches the ImageJ software libraries with methods that greatly reduce the complexity of developing image analysis tools in an interactive 3D visualization environment. In particular, we provide high-level access to volume rendering, volume editing, surface extraction, and image annotation. The ability to rely on a library that removes the low-level details enables concentrating software development efforts on the algorithm implementation parts.

Conclusions

Our framework enables biomedical image software development to be built with 3D visualization capabilities with very little effort. We offer the source code and convenient binary packages along with extensive documentation at http://3dviewer.neurofly.de.

ISOGENIC AUTOSOMES TO BE APPLIED IN OPTIMAL SCREENING FOR NOVEL MUTANTS WITH VIABLE PHENOTYPES INDROSOPHILA MELANOGASTER

Most insertional mutagenesis screens of Drosophila performed to date have not used target chromosomes that have been checked for their suitability for phenotypic screens for viable phenotypes. To address this, we have generated a selection of stocks carrying either isogenized second chromosomes or isogenized third chromosomes, in a genetic background derived from a Canton-S wild-type strain. We have tested these stocks for a range of behavioral and other viable phenotypes. As expected, most lines are statistically indistinguishable from Canton-S in most phenotypes tested. The lines generated are now being used as target chromosomes in mutagenesis screens, and the characterization reported here will facilitate their use in screens of these lines for behavioral and other viable phenotypes.

P90 Ribosomal s6 kinase 2 negatively regulates axon growth in motoneurons

Mutations in Ribosomal s6 kinase 2 (Rsk2) are associated with severe neuronal dysfunction in Coffin-Lowry syndrome (CLS) patients, flies and mice. So far, the mechanisms of how Rsk2 regulates development, maintenance and activity of neurons are not understood. We have investigated the consequences of Rsk2 deficiency in mouse spinal motoneurons. Survival of isolated Rsk2 deficient motoneurons is not reduced, but these cells grow significantly longer neurites. Conversely, overexpression of a constitutively active form of Rsk2 leads to reduced axon growth. Increased axon growth in Rsk2 deficient neurons was accompanied by higher Erk 1/2 phosphorylation, and the knockout phenotype could be rescued by pharmacological inhibition of MAPK/Erk kinase (Mek). These data indicate that Rsk2 negatively regulates axon elongation via the MAPK pathway. Thus, the functional defects observed in the nervous system of CLS patients and animal models with Rsk2 deficiency might be caused by dysregulated neurite growth rather than primary neurodegeneration.

Drosophila RSK negatively regulates bouton number at the neuromuscular junction

Ribosomal S6 kinases (RSKs) are growth factor-regulated serine-threonine kinases participating in the RAS-ERK signaling pathway. RSKs have been implicated in memory formation in mammals and flies. To characterize the function of RSK at the synapse level, we investigated the effect of mutations in the rsk gene on the neuromuscular junction (NMJ) in Drosophila larvae. Immunostaining revealed transgenic expressed RSK in presynaptic regions. In mutants with a full deletion or an N-terminal partial deletion of rsk, an increased bouton number was found. Restoring the wild-type rsk function in the null mutant with a genomic rescue construct reverted the synaptic phenotype, and overexpression of the rsk-cDNA in motoneurons reduced bouton numbers. Based on previous observations that RSK interacts with the Drosophila ERK homologue Rolled, genetic epistasis experiments were performed with loss- and gain-of-function mutations in Rolled. These experiments provided evidence that RSK mediates its negative effect on bouton formation at the Drosophila NMJ by inhibition of ERK signaling.

The central complex of Drosophila melanogaster is involved in flight control: studies on mutants and mosaics of the gene ellipsoid body open

Visual flight control is studied in three mutant alleles of the gene ellipsoid body open (ebo) of Drosophila melanogaster. In mutant ebo flies the central complex is disturbed to varying degrees. Defects range from a small opening in the ellipsoid body to the dissociation of the ring into two parts, a cleft in the fan-shaped body and hypoplasia in the protocerebral bridge. Other parts of the brain are not visibly affected. Flight behavior is normal with respect to the amplitude of the optomotor response and to the object response (single rotating stripe). A reduced amplitude in the small random oscillations of the torque trace (yaw torque activity), however, is found in all three alleles. In two of them the frequency of torque spikes is reduced. In the allele ebo(678) the dynamics of the optomotor response is altered. Upon reversal of the direction of rotation mutant flies take longer than wild type to shift their yaw torque to the new response level (optomotor reversal time). Finally, these flies also behave abnormally in the flight simulator in which their yaw torque controls the angular velocity of the panorama. Many ebo(678) flies fixate a single stripe less persistently than normal flies, some even trying to fly away from it (antifixation). In ebo(678) gynandromorphs the four behavioral phenotypes ("yaw torque activity", "torque spike frequency", "on-target-fixation" and "optomotor reversal time") are all highly correlated with the phenotype of the ellipsoid body. Yaw torque activity and torque spike frequency in addition are correlated with the phenotype of the thorax suggesting that these behavioral defects are in part caused by mutant influences on the ventral ganglion. The results support the hypothesis that the central complex is involved in the control of flight behavior.

Are the structural changes in adult Drosophila mushroom bodies memory traces? Studies on biochemical learning mutants

The pre-imaginal development of Drosophila mushroom bodies is under the influence of an unknown variable which causes populations of wild-type flies at eclosion to differ in the average number of Kenyon cell fibers. During the first week of adult life the number adjusts to an intermediate level which depends upon the experience of the flies. Under olfactory deprivation or social isolation it reaches a lower level than under favorable rearing conditions (J. Neurogenet., 1 (1984) 113-126). The biochemical learning mutants dance and rutabaga show no experience-dependent modulation of fiber number (Fig. 2). In both strains the mushroom bodies of young adults seem to develop abnormally; in dance a loss of about 600 fibers is observed, in rutabaga fiber number is low at eclosion and does not increase (Fig. 1a). The following model for long-term memory is proposed: in mushroom bodies outgrowth and decay of Kenyon cell fibers occur simultaneously. The fibers randomly form transient synapses onto extrinsic output neurons of the mushroom bodies and receive synapses from modulating neurons. Experience consolidates certain synapses, thus prolonging survival of the respective Kenyon cell fibers and increasing the steady state level of fiber number (Fig. 3).

Octopamine in male aggression of Drosophila

BACKGROUND

In mammals and humans, noradrenaline is a key modulator of aggression. Octopamine, a closely related biogenic amine, has been proposed to have a similar function in arthropods. However, the effect of octopamine on aggressive behavior is little understood.

RESULTS

An automated video analysis of aggression in male Drosophila has been developed, rendering aggression accessible to high-throughput studies. The software detects the lunge, a conspicuous behavioral act unique to aggression. In lunging, the aggressor rears up on his hind legs and snaps down on his opponent. By using the software to eliminate confounding effects, we now show that aggression is almost abolished in mutant males lacking octopamine. This suppression is independent of whether tyramine, the precursor of octopamine, is increased or also depleted. Restoring octopamine synthesis in the brain either throughout life or in adulthood leads to a partial rescue of aggression. Finally, neuronal silencing of octopaminergic and tyraminergic neurons almost completely abolishes lunges.

CONCLUSIONS

Octopamine modulates Drosophila aggression. Genetically depleting the animal of octopamine downregulates lunge frequency without a sizable effect on the lunge motor program. This study provides access to the neuronal circuitry mediating this modulation.

Differential potencies of effector genes in adult Drosophila

The GAL4/UAS gene expression system in Drosophila has been crucial in revealing the behavioral significance of neural circuits. Transgene products that block neurotransmitter release and induce cell death have been proved to inhibit neural function powerfully. Here we compare the action of the five effector genes shibire(ts1), Tetanus toxin light chain (TNT), reaper, Diphtheria toxin A-chain (DTA), and inwardly rectifying potassium channel (Kir2.1) and show differences in their efficiency depending on the target cells and the timing of induction. Specifically, effectors blocking neuronal transmission or excitability led to adult-induced paralysis more efficiently than those causing cell ablation. We contrasted these differential potencies in adult to their actions during development. Furthermore, we induced TNT expression in the adult mushroom bodies. In contrast to the successful impairment in short-term olfactory memory by shibire(ts1), adult TNT expression in the same set of cells did not lead to any obvious impairment. Altogether, the efficiency of effector genes depends on properties of the targeted neurons. Thus, we conclude that the selection of the appropriate effector gene is critical for evaluating the function of neural circuits.

The Virtual Insect Brain protocol: creating and comparing standardized neuroanatomy

Background

In the fly Drosophila melanogaster, new genetic, physiological, molecular and behavioral techniques for the functional analysis of the brain are rapidly accumulating. These diverse investigations on the function of the insect brain use gene expression patterns that can be visualized and provide the means for manipulating groups of neurons as a common ground. To take advantage of these patterns one needs to know their typical anatomy.

Results

This paper describes the Virtual Insect Brain (VIB) protocol, a script suite for the quantitative assessment, comparison, and presentation of neuroanatomical data. It is based on the 3D-reconstruction and visualization software Amira, version 3.x (Mercury Inc.) [1]. Besides its backbone, a standardization procedure which aligns individual 3D images (series of virtual sections obtained by confocal microscopy) to a common coordinate system and computes average intensities for each voxel (volume pixel) the VIB protocol provides an elaborate data management system for data administration. The VIB protocol facilitates direct comparison of gene expression patterns and describes their interindividual variability. It provides volumetry of brain regions and helps to characterize the phenotypes of brain structure mutants. Using the VIB protocol does not require any programming skills since all operations are carried out at an intuitively usable graphical user interface. Although the VIB protocol has been developed for the standardization of Drosophila neuroanatomy, the program structure can be used for the standardization of other 3D structures as well.

Conclusion

Standardizing brains and gene expression patterns is a new approach to biological shape and its variability. The VIB protocol provides a first set of tools supporting this endeavor in Drosophila. The script suite is freely available at [2]

Distinct functions of neuronal synaptobrevin in developing and mature fly photoreceptors

Neuronal synaptobrevin (n-Syb, alias VAMP2), a synaptic vesicle membrane protein with a central role in neurotransmission, is specifically cleaved by the light chain of tetanus neurotoxin (TNT) that is known to reliably block neuroexocytosis. Here, we study fly photoreceptors transmitting continuous, graded signals to first order interneurons in the lamina, and report consequences of targeted expression of TNT in these cells using the UAS/GAL4 driver/effector system. Expressing the toxin throughout photoreceptor development causes developmental, electrophysiological, and behavioral defects. These can be differentiated by confining toxin expression to shorter developmental periods. Applying a method for controlled temporal and spatial TNT expression, we found that in the early pupa it impaired the development of the retina; in the midpupa, during synapse formation TNT caused a severe hypoplasia of the lamina that persisted into adulthood and left the photoreceptor-interneuron synapses of the lamina without function. Finally, during adulthood TNT neither blocks synaptic transmission in photoreceptors nor depletes the cells of n-Syb. Our study suggests a novel, cell type-specific function of n-Syb in synaptogenesis and it distinguishes between two synapse types: TNT resistant and TNT sensitive ones. These results need to be taken into account if TNT is used for neural circuit analysis.

Distinct memory traces for two visual features in the Drosophila brain

The fly Drosophila melanogaster can discriminate and remember visual landmarks. It analyses selected parts of its visual environment according to a small number of pattern parameters such as size, colour or contour orientation, and stores particular parameter values. Like humans, flies recognize patterns independently of the retinal position during acquisition of the pattern (translation invariance). Here we show that the central-most part of the fly brain, the fan-shaped body, contains parts of a network mediating visual pattern recognition. We have identified short-term memory traces of two pattern parameters--elevation in the panorama and contour orientation. These can be localized to two groups of neurons extending branches as parallel, horizontal strata in the fan-shaped body. The central location of this memory store is well suited to mediate translational invariance.

The S6KII (rsk) gene of Drosophila melanogaster differentially affects an operant and a classical learning task

In an attempt to dissect classical and operant conditioning in Drosophila melanogaster, we have isolated the gene for ribosomal S6 kinase II (S6KII). This enzyme is part of a family of serine-threonine kinases that in mammals have been implicated in the MAPK (mitogen-activated protein kinase) signaling cascade controlling (among other processes) synaptic plasticity (long-term potentiation/long-term depression) and memory formation. The human homolog rsk2 has been linked to mental retardation (Coffin-Lowry syndrome). Mutant analysis in Drosophila shows that S6KII serves different functions in operant place learning and classical (pavlovian) olfactory conditioning. Whereas in the null mutant only pavlovian olfactory learning is affected, a P-element insertion mutant reducing the amount of S6KII only affects operant place learning. A mutant lacking part of the N-terminal kinase domain and performing poorly in both learning tasks is dominant in the operant paradigm and recessive in the pavlovian paradigm. The behavioral defects in the pavlovian task can be rescued by the genomic S6KII transgene. Overexpression of S6KII in wild type has a dominant-negative effect on the operant task that is rescued by the null mutant, whereas in the pavlovian task overexpression may even enhance learning performance.

The DrosDel collection: a set of P-element insertions for generating custom chromosomal aberrations in Drosophila melanogaster

We describe a collection of P-element insertions that have considerable utility for generating custom chromosomal aberrations in Drosophila melanogaster. We have mobilized a pair of engineered P elements, p[RS3] and p[RS5], to collect 3243 lines unambiguously mapped to the Drosophila genome sequence. The collection contains, on average, an element every 35 kb. We demonstrate the utility of the collection for generating custom chromosomal deletions that have their end points mapped, with base-pair resolution, to the genome sequence. The collection was generated in an isogenic strain, thus affording a uniform background for screens where sensitivity to genetic background is high. The entire collection, along with a computational and genetic toolbox for designing and generating custom deletions, is publicly available. Using the collection it is theoretically possible to generate >12,000 deletions between 1 bp and 1 Mb in size by simple eye color selection. In addition, a further 37,000 deletions, selectable by molecular screening, may be generated. We are now using the collection to generate a second-generation deficiency kit that is precisely mapped to the genome sequence.

An engram found? Evaluating the evidence from fruit flies

Is it possible to localize a memory trace to a subset of cells in the brain? If so, it should be possible to show: first, that neuronal plasticity occurs in these cells. Second, that neuronal plasticity in these cells is sufficient for memory. Third, that neuronal plasticity in these cells is necessary for memory. Fourth, that memory is abolished if these cells cannot provide output during testing. And fifth, that memory is abolished if these cells cannot receive input during training. With regard to olfactory learning in flies, we argue that the notion of the olfactory memory trace being localized to the Kenyon cells of the mushroom bodies is a reasonable working hypothesis.

Disruption of the MAP1B-related protein FUTSCH leads to changes in the neuronal cytoskeleton, axonal transport defects, and progressive neurodegeneration in Drosophila

The elaboration of neuronal axons and dendrites is dependent on a functional cytoskeleton. Cytoskeletal components have been shown to play a major role in the maintenance of the nervous system through adulthood, and changes in neurofilaments and microtubule-associated proteins (MAPs) have been linked to a variety of neurodegenerative diseases. Here we show that Futsch, the fly homolog of MAP1B, is involved in progressive neurodegeneration. Although Futsch is widely expressed throughout the CNS, degeneration in futsch(olk) primarily occurs in the olfactory system and mushroom bodies. Consistent with the predicted function of Futsch, we find abnormalities in the microtubule network and defects in axonal transport. Degeneration in the adult brain is preceded by learning deficits, revealing a neuronal dysfunction before detectable levels of cell death. Futsch is negatively regulated by the Drosophila Fragile X mental retardation gene, and a mutation in this gene delays the onset of neurodegeneration in futsch(olk). A similar effect is obtained by expression of either fly or bovine tau, suggesting a certain degree of functional redundancy of MAPs. The futsch(olk) mutants exhibit several characteristics of human neurodegenerative diseases, providing an opportunity to study the role of MAPs in progressive neurodegeneration within an experimentally accessible, in vivo model system.

The carrot, not the stick: appetitive rather than aversive gustatory stimuli support associative olfactory learning in individually assayed Drosophila larvae

The ability to learn is universal among animals; we investigate associative learning between odors and "tastants" in larval Drosophila melanogaster. As biologically important gustatory stimuli, like sugars, salts, or bitter substances have many behavioral functions, we investigate not only their reinforcing function, but also their response-modulating and response-releasing function. Concerning the response-releasing function, larvae are attracted by fructose and repelled by sodium chloride and quinine; also, fructose increases, but salt and quinine suppress feeding. However, none of these stimuli has a nonassociative, modulatory effect on olfactory choice behavior. Finally, only fructose but neither salt nor quinine has a reinforcing effect in associative olfactory learning. This implies that the response-releasing, response-modulating and reinforcing functions of these tastants are dissociated on the behavioral level. These results open the door to analyze how this dissociation is brought about on the cellular and molecular level; this should be facilitated by the cellular simplicity and genetic accessibility of the Drosophila larva.

Flies lacking all synapsins are unexpectedly healthy but are impaired in complex behaviour

Vertebrate synapsins are abundant synaptic vesicle phosphoproteins that have been proposed to fine-regulate neurotransmitter release by phosphorylation-dependent control of synaptic vesicle motility. However, the consequences of a total lack of all synapsin isoforms due to a knock-out of all three mouse synapsin genes have not yet been investigated. In Drosophila a single synapsin gene encodes several isoforms and is expressed in most synaptic terminals. Thus the targeted deletion of the synapsin gene of Drosophila eliminates the possibility of functional knock-out complementation by other isoforms. Unexpectedly, synapsin null mutant flies show no obvious defects in brain morphology, and no striking qualitative changes in behaviour are observed. Ultrastructural analysis of an identified 'model' synapse of the larval nerve muscle preparation revealed no difference between wild-type and mutant, and spontaneous or evoked excitatory junction potentials at this synapse were normal up to a stimulus frequency of 5 Hz. However, when several behavioural responses were analysed quantitatively, specific differences between mutant and wild-type flies are noted. Adult locomotor activity, optomotor responses at high pattern velocities, wing beat frequency, and visual pattern preference are modified. Synapsin mutant flies show faster habituation of an olfactory jump response, enhanced ethanol tolerance, and significant defects in learning and memory as measured using three different paradigms. Larval behavioural defects are described in a separate paper. We conclude that Drosophila synapsins play a significant role in nervous system function, which is subtle at the cellular level but manifests itself in complex behaviour.

Identification of mushroom body miniature, a zinc-finger protein implicated in brain development of Drosophila

The mushroom bodies are bilaterally arranged structures in the protocerebrum of Drosophila and most other insect species. Mutants with altered mushroom body structure have been instrumental not only in establishing their role in distinct behavioral functions but also in identifying the molecular pathways that control mushroom body development. The mushroom body miniature(1) (mbm(1)) mutation results in grossly reduced mushroom bodies and odor learning deficits in females. With a survey of genomic rescue constructs, we have pinpointed mbm(1) to a single transcription unit and identified a single nucleotide exchange in the 5' untranslated region of the corresponding transcript resulting in a reduced expression of the protein. The most obvious feature of the Mbm protein is a pair of C(2)HC zinc fingers, implicating a function of the protein in binding nucleic acids. Immunohistochemical analysis shows that expression of the Mbm protein is not restricted to the mushroom bodies. BrdUrd labeling experiments indicate a function of Mbm in neuronal precursor cell proliferation.

Visual pattern recognition in Drosophila is invariant for retinal position

Vision relies on constancy mechanisms. Yet, these are little understood, because they are difficult to investigate in freely moving organisms. One such mechanism, translation invariance, enables organisms to recognize visual patterns independent of the region of their visual field where they had originally seen them. Tethered flies (Drosophila melanogaster) in a flight simulator can recognize visual patterns. Because their eyes are fixed in space and patterns can be displayed in defined parts of their visual field, they can be tested for translation invariance. Here, we show that flies recognize patterns at retinal positions where the patterns had not been presented before.

Event timing turns punishment to reward

Can relief from pain be a pleasure? If so, noxious events should--despite their typically aversive effects--also have a 'rewarding' after-effect. Through training fruitflies by using an electric shock paired with an odour, we show here that the shock can condition either avoidance of this odour or approach to it. These opposing behaviours depend on the relative timing of the shock and odour presentations during training, and indicate that a shock can act as either an aversive reinforcer or an appetitive one.

[Architecture of the X chromosome, expression of LIM kinase 1, and recombination in the agnostic mutants of Drosophila: a model of human Williams syndrome]

As the Human Genome and Drosophila Genome Projects were completed, it became clear that functions of human disease-associated genes may be elucidated by studying the phenotypic expression of mutations affecting their structural or functional homologs in Drosophila. Genomic diseases were identified as a new class of human disorders. Their cause is recombination, which takes place at gene-flanking duplicons to generate chromosome aberrations such as deletions, duplications, inversions, and translocations. The resulting imbalance of the dosage of developmentally important genes arises at a frequency of 10(-3) (higher than the mutation rate of individual genes) and leads to syndromes with multiple manifestations, including cognitive defects. Genomic DNA fragments were cloned from the Drosophila melanogaster agnostic locus, whose mutations impair learning ability and memory. As a result, the locus was exactly localized in X-chromosome region 11A containing the LIM kinase 1 (LIMK1) gene (CG1848), which is conserved among many species. Hemizygosity for the LIMK1 gene, which is caused by recombination at neighboring extended repeats, underlies cognitive disorders in human Williams syndrome. LIMK1 is a component of the integrin signaling cascade, which regulates the functions of the actin cytoskeleton, synaptogenesis, and morphogenesis in the developing brain. Immunofluorescence analysis revealed LIMK1 in all subdomains of the central complex and the visual system of Drosophila melanogaster. Like in the human genome, the D. melanogaster region is flanked by numerous repeats, which were detected by molecular genetic methods and analysis of ectopic chromosome pairing. The repeats determined a higher rate of spontaneous and induced recombination. including unequal crossing over, in the agnostic gene region. Hence, the agnostic locus was considered as the first D. melanogaster model suitable for studying the genetic defect associated with Williams syndrome in human.

Visual learning in individually assayed Drosophila larvae

An understanding of associative learning is facilitated if it can be analyzed in a simple animal like the fruit fly Drosophila. Here, we introduce the first visual associative learning paradigm for larval Drosophila; this is remarkable as larvae have an order of magnitude fewer neurons than adult flies. Larvae were subjected to either of two reciprocal training regimes: Light+/Dark- or Light-/Dark+. Subsequently, all larvae were individually tested for their preference between Light versus Dark. The difference between training regimes was therefore exclusively which visual situation was associated with which reinforcer;differences observed during the test thus reflected exclusively associative learning. For positive reinforcement (+) we used fructose (FRU), and for negative reinforcement (-) either quinine or sodium chloride (QUI, NaCl). Under these conditions, associative learning could be reproducibly observed in both wild-type strains tested. We then compared the effectiveness of training using differential conditioning, with both positive and negative reinforcement, to that using only positive or only negative reinforcement. We found that FRU only, but neither QUI nor NaCl, was in itself effective as a reinforcer. This is the first demonstration of appetitive learning in larval Drosophila. It is now possible to investigate the behavioral and neuronal organization of appetitive visual learning in this simple and genetically easy-to-manipulate experimental system.

Dopamine and octopamine differentiate between aversive and appetitive olfactory memories in Drosophila

The catecholamines play a major role in the regulation of behavior. Here we investigate, in the fly Drosophila melanogaster, the role of dopamine and octopamine (the presumed arthropod homolog of norepinephrine) during the formation of appetitive and aversive olfactory memories. We find that for the formation of both types of memories, cAMP signaling is necessary and sufficient within the same subpopulation of mushroom-body intrinsic neurons. On the other hand, memory formation can be distinguished by the requirement for different catecholamines, dopamine for aversive and octopamine for appetitive conditioning. Our results suggest that in associative conditioning, different memories are formed of the same odor under different circumstances, and that they are linked to the respective motivational systems by their specific modulatory pathways.

The role of central parts of the brain in the control of sound production during courtship in Drosophila melanogaster

The question of the roles of the two main parts of the insect brain, the mushroom bodies and the central complex, in controlling motor coordination and triggering a variety of behavioral programs, including sound production, remains controversial. With the aim of improving our understanding of this question, we studied the parameters of songs used by five-day-old males during courtship for fertilized wild-type females (Canton-S, C-S) over 5-min periods at 25 degrees C; males were of two wild-type Drosophila melanogaster lines (Berlin and C-S). Berlin males lacking mushroom bodies because of treatment with hydroxyurea during development (chemical removal of the mushroom bodies) were used, along with two mutants with defects in the mushroom bodies (mbm1 and mud1), two mutants with defects in the central complex (ccbKS127 and cexKS181), and mutant cxbN71 with defects in both the mushroom bodies and the central complex. The experiments reported here showed that courtship songs in males lacking mushroom bodies were virtually identical to those of wild-type males. The main parameters of pulsatile song in mutants mbm1 and mud1 (interpulse interval and train duration) were insignificantly different from those of the songs of wild-type flies, though the stability of the pulse oscillator was the same. Flies of these lines were no different from wild-type flies in terms of courtship success (percentage of copulating pairs in 10-min tests). Conversely, the songs of mutants with defects in the central complex differed from those of wild-type males. Firstly, there was degradation of the stability of the pulse oscillator and interpulse intervals were very variable. In addition, pulses were often significantly longer and appeared multicyclic, as in the well-known cacophony mutant, while the mean train duration was significantly shorter. Males of the line cexKS181 usually courted very intensely, though abnormal sounds were generally emitted. Mutants cexKS181 and ccbKS127 were significantly less successful in courtship than wild-type flies. These data show that the central complex appears to play a very important role in controlling song, while the mushroom bodies are not related to this function.

Memories in drosophila heat-box learning

Learning and memory processes of operant conditioning in the heat-box are analyzed. In a search for conditioning parameters leading to high retention scores, intermittent training is shown to give better results than those of continuous training. Immediate retention tests contain two memory components, a spatial preference for one side of the chamber and a "stay-where-you-are-effect." Intermittent training strengthens the latter. In the second part, memory dynamics is investigated. Flies are trained in one chamber and tested in a second one after a brief reminder training. With this direct transfer, memory scores reflect an associative learning process in the first chamber. To investigate memory retention after extended time periods, indirect transfer experiments are performed. The fly is transferred to a different environment between training and test phases. With this procedure, an aftereffect of the training can still be observed 2 h later. Surprisingly, exposure to the chamber without conditioning also leads to a memory effect in the indirect transfer experiment. This exposure effect reveals a dispositional change that facilitates operant learning during the reminder training. The various memory effects are independent of the mushroom bodies.