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Dive into the research topics where Simon G. Sprecher is active.

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Featured researches published by Simon G. Sprecher.


Nature | 2008

Switch of rhodopsin expression in terminally differentiated Drosophila sensory neurons

Simon G. Sprecher; Claude Desplan

Specificity of sensory neurons requires restricted expression of one sensory receptor gene and the exclusion of all others within a given cell. In the Drosophila retina, functional identity of photoreceptors depends on light-sensitive Rhodopsins (Rhs). The much simpler larval eye (Bolwig organ) is composed of about 12 photoreceptors, eight of which are green-sensitive (Rh6) and four blue-sensitive (Rh5). The larval eye becomes the adult extraretinal ‘eyelet’ composed of four green-sensitive (Rh6) photoreceptors. Here we show that, during metamorphosis, all Rh6 photoreceptors die, whereas the Rh5 photoreceptors switch fate by turning off Rh5 and then turning on Rh6 expression. This switch occurs without apparent changes in the programme of transcription factors that specify larval photoreceptor subtypes. We also show that the transcription factor Senseless (Sens) mediates the very different cellular behaviours of Rh5 and Rh6 photoreceptors. Sens is restricted to Rh5 photoreceptors and must be excluded from Rh6 photoreceptors to allow them to die at metamorphosis. Finally, we show that Ecdysone receptor (EcR) functions autonomously both for the death of larval Rh6 photoreceptors and for the sensory switch of Rh5 photoreceptors to express Rh6. This fate switch of functioning, terminally differentiated neurons provides a novel, unexpected example of hard-wired sensory plasticity.


PLOS ONE | 2012

The serotonergic central nervous system of the Drosophila larva: anatomy and behavioral function

Annina Huser; Astrid Rohwedder; Anthi A. Apostolopoulou; Annekathrin Widmann; Johanna E. Pfitzenmaier; Elena M. Maiolo; Mareike Selcho; Dennis Pauls; Alina von Essen; Tripti Gupta; Simon G. Sprecher; Serge Birman; Thomas Riemensperger; Reinhard F. Stocker; Andreas S. Thum

The Drosophila larva has turned into a particularly simple model system for studying the neuronal basis of innate behaviors and higher brain functions. Neuronal networks involved in olfaction, gustation, vision and learning and memory have been described during the last decade, often up to the single-cell level. Thus, most of these sensory networks are substantially defined, from the sensory level up to third-order neurons. This is especially true for the olfactory system of the larva. Given the wealth of genetic tools in Drosophila it is now possible to address the question how modulatory systems interfere with sensory systems and affect learning and memory. Here we focus on the serotonergic system that was shown to be involved in mammalian and insect sensory perception as well as learning and memory. Larval studies suggested that the serotonergic system is involved in the modulation of olfaction, feeding, vision and heart rate regulation. In a dual anatomical and behavioral approach we describe the basic anatomy of the larval serotonergic system, down to the single-cell level. In parallel, by expressing apoptosis-inducing genes during embryonic and larval development, we ablate most of the serotonergic neurons within the larval central nervous system. When testing these animals for naïve odor, sugar, salt and light perception, no profound phenotype was detectable; even appetitive and aversive learning was normal. Our results provide the first comprehensive description of the neuronal network of the larval serotonergic system. Moreover, they suggest that serotonin per se is not necessary for any of the behaviors tested. However, our data do not exclude that this system may modulate or fine-tune a wide set of behaviors, similar to its reported function in other insect species or in mammals. Based on our observations and the availability of a wide variety of genetic tools, this issue can now be addressed.


Proceedings of the National Academy of Sciences of the United States of America | 2015

Sensory determinants of behavioral dynamics in Drosophila thermotaxis

Mason Klein; Bruno Afonso; Ashley J. Vonner; Luis Hernandez-Nunez; Matthew E. Berck; Christopher J. Tabone; Elizabeth Anne Kane; Vincent A. Pieribone; Michael N. Nitabach; Albert Cardona; Marta Zlatic; Simon G. Sprecher; Marc Gershow; Paul A. Garrity; Aravinthan D. T. Samuel

Significance A previously unidentified set of thermosensory neurons embedded in the olfactory organ of the Drosophila larva is shown to be required to drive the animal up temperature gradients toward preferred environments. Optogenetics and optical neurophysiology reveal efficient sensory encoding of both favorable (warming) and unfavorable (cooling) stimuli for distinct components of thermotactic strategy by this one set of neurons. Cooling-evoked activation is used to curtail forward movements in unfavorable directions; warming-evoked deactivation is used to orient new forward movements in favorable directions during turns. Our results pinpoint the locus of thermosensory perception for cool-avoidance behavior in the larva and define how downstream circuits use thermosensory perception to organize navigational behavior. Complex animal behaviors are built from dynamical relationships between sensory inputs, neuronal activity, and motor outputs in patterns with strategic value. Connecting these patterns illuminates how nervous systems compute behavior. Here, we study Drosophila larva navigation up temperature gradients toward preferred temperatures (positive thermotaxis). By tracking the movements of animals responding to fixed spatial temperature gradients or random temperature fluctuations, we calculate the sensitivity and dynamics of the conversion of thermosensory inputs into motor responses. We discover three thermosensory neurons in each dorsal organ ganglion (DOG) that are required for positive thermotaxis. Random optogenetic stimulation of the DOG thermosensory neurons evokes behavioral patterns that mimic the response to temperature variations. In vivo calcium and voltage imaging reveals that the DOG thermosensory neurons exhibit activity patterns with sensitivity and dynamics matched to the behavioral response. Temporal processing of temperature variations carried out by the DOG thermosensory neurons emerges in distinct motor responses during thermotaxis.


Proceedings of the National Academy of Sciences of the United States of America | 2013

Sensorimotor structure of Drosophila larva phototaxis

Elizabeth Anne Kane; Marc Gershow; Bruno Afonso; Ivan Larderet; Mason Klein; Ashley R. Carter; Benjamin L. de Bivort; Simon G. Sprecher; Aravinthan D. T. Samuel

Significance Small animals such as Drosophila provide an opportunity to understand the neural circuitry for complex behaviors from sensory input to motor output without gaps. Here, we define the algorithms for Drosophila larva phototaxis (i.e., the maps between sensory input and motor output) by quantifying the movements of individual animals responding to a battery of illumination conditions. Surprisingly, the distinct rules that define different components of the overall photosensory response begin to segregate at the first synapses after the photoreceptor cells. These results lay the foundation for mapping the circuits for phototaxis in the compact nervous system of the larva by first elucidating the algorithms that define behavior and then mapping these algorithms to specific circuit pathways. The avoidance of light by fly larvae is a classic paradigm for sensorimotor behavior. Here, we use behavioral assays and video microscopy to quantify the sensorimotor structure of phototaxis using the Drosophila larva. Larval locomotion is composed of sequences of runs (periods of forward movement) that are interrupted by abrupt turns, during which the larva pauses and sweeps its head back and forth, probing local light information to determine the direction of the successive run. All phototactic responses are mediated by the same set of sensorimotor transformations that require temporal processing of sensory inputs. Through functional imaging and genetic inactivation of specific neurons downstream of the sensory periphery, we have begun to map these sensorimotor circuits into the larval central brain. We find that specific sensorimotor pathways that govern distinct light-evoked responses begin to segregate at the first relay after the photosensory neurons.


The Journal of Neuroscience | 2011

Distinct Visual Pathways Mediate Drosophila Larval Light Avoidance and Circadian Clock Entrainment

Alex C. Keene; Esteban O. Mazzoni; Jamie Zhen; Meg A. Younger; Satoko Yamaguchi; Justin Blau; Claude Desplan; Simon G. Sprecher

Visual organs perceive environmental stimuli required for rapid initiation of behaviors and can also entrain the circadian clock. The larval eye of Drosophila is capable of both functions. Each eye contains only 12 photoreceptors (PRs), which can be subdivided into two subtypes. Four PRs express blue-sensitive rhodopsin5 (rh5) and eight express green-sensitive rhodopsin6 (rh6). We found that either PR-subtype is sufficient to entrain the molecular clock by light, while only the Rh5-PR subtype is essential for light avoidance. Acetylcholine released from PRs confers both functions. Both subtypes of larval PRs innervate the main circadian pacemaker neurons of the larva, the neuropeptide PDF (pigment-dispersing factor)-expressing lateral neurons (LNs), providing sensory input to control circadian rhythms. However, we show that PDF-expressing LNs are dispensable for light avoidance, and a distinct set of three clock neurons is required. Thus we have identified distinct sensory and central circuitry regulating light avoidance behavior and clock entrainment. Our findings provide insights into the coding of sensory information for distinct behavioral functions and the underlying molecular and neuronal circuitry.


Trends in Neurosciences | 2012

Seeing the light: photobehavior in fruit fly larvae

Alex C. Keene; Simon G. Sprecher

Understanding how sensory stimuli drive behavior requires a detailed understanding of the molecular and neural nature through which the stimuli are received and processed. The visual system of the fruit fly Drosophila melanogaster shares marked similarities to that of mammals. Although much focus has been given to the fly visual system, an even further simplified eye and brain makes the visual system of Drosophila larvae an excellent model for dissecting sensory processing and behavioral responses to light. Recent work has identified sensory and central brain neurons required for larval visual behaviors, including circadian rhythms. Here, we review the genes and neurons regulating visual processing in Drosophila larvae and discuss the implications of this work for furthering understanding of more complex visual systems.


Developmental Dynamics | 2012

Genetic and developmental mechanisms underlying the formation of the Drosophila compound eye

Maria Tsachaki; Simon G. Sprecher

The compound eye of Drosophila melanogaster consists of individual subunits (“ommatidia”), each containing photoreceptors and support cells. These cells derive from an undifferentiated epithelium in the eye imaginal disc and their differentiation follows a highly stereotypic pattern. Sequential commitment of pluripotent cells to become specialized cells of the visual system serves as a unique model system to study basic mechanisms of tissue development. In the past years, many regulatory genes that govern the development of the compound eye have been identified and their mode of action genetically dissected. Transcription factor networks in combination with cell–cell signalling pathways regulate the development of the eye tissue in a precise temporal and spatial manner. Here, we review the recent advances on how a single‐cell‐layered epithelium is patterned to give rise to the compound eye. We discuss the molecular pathways controlling differentiation of individual photoreceptors, through which they acquire their functional specificity. Developmental Dynamics 241:40–56, 2012.


Developmental Biology | 2011

The Drosophila larval visual system: High-resolution analysis of a simple visual neuropil

Simon G. Sprecher; Albert Cardona; Volker Hartenstein

The task of the visual system is to translate light into neuronal encoded information. This translation of photons into neuronal signals is achieved by photoreceptor neurons (PRs), specialized sensory neurons, located in the eye. Upon perception of light the PRs will send a signal to target neurons, which represent a first station of visual processing. Increasing complexity of visual processing stems from the number of distinct PR subtypes and their various types of target neurons that are contacted. The visual system of the fruit fly larva represents a simple visual system (larval optic neuropil, LON) that consists of 12 PRs falling into two classes: blue-senstive PRs expressing Rhodopsin 5 (Rh5) and green-sensitive PRs expressing Rhodopsin 6 (Rh6). These afferents contact a small number of target neurons, including optic lobe pioneers (OLPs) and lateral clock neurons (LNs). We combine the use of genetic markers to label both PR subtypes and the distinct, identifiable sets of target neurons with a serial EM reconstruction to generate a high-resolution map of the larval optic neuropil. We find that the larval optic neuropil shows a clear bipartite organization consisting of one domain innervated by PRs and one devoid of PR axons. The topology of PR projections, in particular the relationship between Rh5 and Rh6 afferents, is maintained from the nerve entering the brain to the axon terminals. The target neurons can be subdivided according to neurotransmitter or neuropeptide they use as well as the location within the brain. We further track the larval optic neuropil through development from first larval instar to its location in the adult brain as the accessory medulla.


Arthropod Structure & Development | 2003

The urbilaterian brain : developmental insights into the evolutionary origin of the brain in insects and vertebrates

Simon G. Sprecher; Heinrich Reichert

Classical phylogenetic, neuroanatomical and neuroembryological studies propose an independent evolutionary origin of the brains of insects and vertebrates. Contrasting with this, data from three sets of molecular and genetic analyses indicate that the developmental program of brains of insects and vertebrates might be highly conserved and suggest a monophyletic origin of the brain of protostomes and deuterostomes. First, recent results of molecular phylogeny imply that none of the currently living animals correspond to evolutionary intermediates between protostomes and deuterostomes, thus making it impossible to infer the morphological organization of an ancestral bilaterian brain from living specimens. Second, recent molecular genetic evidence provides support for the body axis inversion hypothesis, which implies that a dorsoventral inversion of the body axis occurred in protostomes versus deuterostomes, leading to the inverted location of neurogenic regions in these animal groups. Third, recent developmental genetic analyses are uncovering the existence of structurally and functionally homologous genes that have comparable and interchangeable functions in early brain development in insect and vertebrate model systems. Thus, development of the anteriormost part of the embryonic brain in both insects and vertebrates depends upon the otd/Otx and ems/Emx genes; development of the posterior part of the embryonic brain in both insects and vertebrates involves homologous control genes of the Hox cluster. These findings, which demonstrate the conserved expression and function of key patterning genes involved in embryonic brain development in insects and vertebrates support the hypothesis that the brains of protostomes and deuterostomes are of monophyletic, urbilaterian origin.


Nature | 2011

Feedback from rhodopsin controls rhodopsin exclusion in Drosophila photoreceptors

Daniel Vasiliauskas; Esteban O. Mazzoni; Simon G. Sprecher; Konstantin Brodetskiy; Robert J. Johnston; Preetmoninder Lidder; Nina Vogt; Arzu Celik; Claude Desplan

Sensory systems with high discriminatory power use neurons that express only one of several alternative sensory receptor proteins. This exclusive receptor gene expression restricts the sensitivity spectrum of neurons and is coordinated with the choice of their synaptic targets. However, little is known about how it is maintained throughout the life of a neuron. Here we show that the green-light sensing receptor rhodopsin 6 (Rh6) acts to exclude an alternative blue-sensitive rhodopsin 5 (Rh5) from a subset of Drosophila R8 photoreceptor neurons. Loss of Rh6 leads to a gradual expansion of Rh5 expression into all R8 photoreceptors of the ageing adult retina. The Rh6 feedback signal results in repression of the rh5 promoter and can be mimicked by other Drosophila rhodopsins; it is partly dependent on activation of rhodopsin by light, and relies on Gαq activity, but not on the subsequent steps of the phototransduction cascade. Our observations reveal a thus far unappreciated spectral plasticity of R8 photoreceptors, and identify rhodopsin feedback as an exclusion mechanism.

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Boris Egger

University of Fribourg

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