Biology subjects

Sprecher, S. G.

Publications and source records attributed to Sprecher, S. G..

12 recordsLinked to original sources

bioRxiv2025

The Ataxin-2 protein is required in Kenyon cells for RNP-granule assembly and appetitive long-term memory formation.

Ribonucleo-protein granules (mRNP granules) are thought to contribute to the control of neuronal mRNA translation required for consolidation of long-term memories. Consistent with this, the function of Ataxin-2 in mRNA granule assembly has been shown to be required for long-term olfactory habituation (LTH) in Drosophila, a form of non-associative memory. Knockdown of Ataxin-2 in either local interneurons (LNs) or projection neurons (PNs) of the insect antennal lobe disrupts LTH, leading to a model in which Ataxin-dependent translational control is required in both presynaptic and postsynaptic elements of the LN-PN synapse, whose potentiation has been causally linked to LTH. Here we use novel and established methods for cell-type specific perturbation to ask: (a) whether Ataxin-2 controls mRNA granule assembly in cell types beyond the few that have been examined; and (b) whether it functions not only in LTH, but also for long-term olfactory associative memory (LTM). We show that Ataxin-2 controls mRNP granule assembly in additional neuronal types, namely Kenyon Cells that encode associative memory, as well as more broadly in non-neuronal cells, e.g. in nurse cells in the egg chamber. Furthermore, selective knockdown of Atx2 in /{beta} and /{beta} KCs blocks appetitive long-term but not short-term associative memories. Taken together these observations support a hypothesis that Ataxin-2 dependent translational control is widely required across different mnemonic circuits for consolidation of respective forms of long-term memories.

neuroscience↗

bioRxiv2025

Sensory discrimination of chemical and temperature stimuli in the acoel Symsagittifera roscoffensis

Environmental cues provide critical sensory information for the survival of animals. Understanding how distinct sensory cues elicit or modulate certain behaviour thus provides insights into the neuronal adaptations to rapid and continuous changes in the surrounding world. Intertidal ecosystems are a particularly exposed to environmental fluctuations. Due to changing exposure to seawater, animals are subjected to continuous fluctuations of temperature or salinity during the course of day-night and tidal cycles. Animals in the intertidal environment show physiological and behavioural adaptations to these changes. When the acoel Symsagittifera roscoffensis is exposed to daylight during the tidal cycle, these animals are found at the surface of sandy beaches, which enhance the exposure of their photosynthetic algal (Tetraselmis convolutae) symbionts to light. Moreover, S. roscoffensis shows a strong positive phototactic displacement as well as both positive and negative geotaxis, both being evolved behavioural adaptations to enhance light-exposure for its photosymbiont. Currently little is known about other sensory systems and their functions in S. roscoffensis. In this study, we probe sensory capabilities of S. roscoffensis focusing on chemical and temperature cues. Our findings support that S. roscoffensis shows avoidance behaviours to increased temperature and high salinity, preferring cooler environments with lower salinity.

animal behavior and cognition↗

bioRxiv2024

Food texture preference reveals multisensory contributions of gustatory organs in behaviour and physiology

Food presents a multisensory experience, with visual, taste, and olfactory cues being important in allowing an animal to determine the safety and nutritional value of a given substance1. Texture, however, remains a surprisingly unexplored aspect, despite providing key information about the state of the food through properties such as hardness, liquidity, and granularity. Food perception is achieved by specialised sensory neurons, which themselves are defined by the receptor genes they express. While it was assumed that sensory neurons respond to one or few closely-related stimuli, more recent findings challenge this notion and support evidence that certain sensory neurons are more broadly tuned. In the Drosophila taste system, gustatory neurons respond to cues of opposing hedonic valence or to olfactory cues. Here, we identified that larvae ingest and navigate towards specific food substrate hardnesses, and probed the role of gustatory organs in this behaviour. By developing a genetic tool targeting specifically gustatory organs, we show that these organs are major contributors for evaluation of food texture and ingestion decision-making. We find that ablation of gustatory organs not only results in loss of chemosensation, but also navigation and ingestion preference to varied substrate textures. Furthermore, we show that certain neurons in the primary taste organ exhibit varied and concurrent physiological responses to mechanical and multimodal stimulation. We show that individual neurons house independent mechanisms for multiple sensory modalities, challenging assumptions about capabilities of sensory neurons. We propose that further investigations, across the animal kingdom, may reveal higher sensory complexity than currently anticipated.

neuroscience↗

bioRxiv2024

A temporally restricted function of the Dopamine receptor Dop1R2 during memory formation

Dopamine is a crucial neuromodulator involved in many brain processes, including learning and the formation of memories. Dopamine acts through multiple receptors and controls an intricate signaling network to regulate different tasks. While the diverse functions of dopamine are intensely studied, the interplay and role of the distinct dopamine receptors to regulate different processes is less well understood. An interesting candidate is the dopamine receptor Dop1R2 (also known as Damb), as it could connect to different downstream pathways. Dop1R2 is reported to be involved in forgetting and memory maintenance, however, the circuits requiring the receptors are unknown. To study Dop1R2 and its role in specific spatial and temporal contexts, we generated a conditional knock-out line using the CRISPR-Cas9 technique. Two FRT sites were inserted, allowing flippase-mediated excision of the dopamine receptor in neurons of interest. To study the function of Dop1R2, we knocked it out conditionally in the Mushroom body of Drosophila melanogaster, a well-studied brain region for memory formation. We show that Dop1R2 is required for later memory forms but not for short-term aversive or appetitive memories. Moreover, Dop1R2 is specifically required in the alpha'/beta'-lobe and the alpha/beta-lobe but not in the gamma-lobe of the Mushroom body. Our findings show a spatially and temporally restricted role of Dop1R2 in the process of memory formation highlighting the differential requirement of receptors during distinct phases of learning.

neuroscience↗

bioRxiv2022

Memory phase-specific genes in the Mushroom Bodies identified using CrebB-target DamID

The formation of long-term memories requires changes in the transcriptional program and de novo protein synthesis. One of the critical regulators for long-term memory (LTM) formation and maintenance is the transcription factor CREB. Genetic studies have dissected the requirement of CREB activity within memory circuits, however less is known about the genetic mechanisms acting downstream of CREB and how they may contribute defining LTM phases. To better understand the downstream mechanisms, we here used a targeted DamID approach (TaDa). We generated a CREB-Dam fusion protein using the fruit fly Drosophila melanogaster as model. Expressing CREB-Dam in the mushroom bodies (MBs), a brain center implicated in olfactory memory formation, we identified genes that are differentially expressed between paired and unpaired appetitive training paradigm. Of those genes we selected candidates for an RNAi screen in which we identified genes causing increased or decreased LTM.

neuroscience↗

bioRxiv2022

Molecular characterization of cell types in the squid Loligo vulgaris

Cephalopods have long been getting a lot of attention for their fascinating behavioral abilities and for the complexity of their nervous systems that set them apart from other mollusks. Because of the great evolutionary distance that separates vertebrates from mollusks, it is evident that higher cognitive features have evolved independently in this clade although they sometimes resemble cognitive functions of vertebrates. Alongside their complex behavioral abilities, cephalopods have evolved specialized cells and tissues, such as the chromatophores for camouflage or suckers to grasp prey. Gaining a better understanding of the biology of various species of cephalopods can significantly improve our knowledge of how these animals evolved and better identify the mechanisms that drive the astonishing faculties of their nervous systems. In this study, we performed single-cell transcriptomics of whole heads of Loligo vulgaris pre-hatchlings. We characterized the different cell types in the head of these animals and explored the expression patterns of core cell type markers by hybridization chain reaction. We were able to thoroughly describe some major components of the squid nervous that play important roles for the maintenance, development and sensory function in the nervous system of these animals.

developmental biology↗

bioRxiv2021

Homothorax Controls a Binary Rhodopsin Switch in Drosophila Ocelli

Visual perception of the environment is mediated by specialized photoreceptor (PR) neurons of the eye. Each PR expresses photosensitive opsins, which are activated by a particular wavelength of light. In most insects, the visual system comprises a pair of compound eyes that are mainly associated with motion detection, color or polarized light perception and a triplet of ocelli that are thought to be critical during flight to detect horizon and movements. It is widely believed that evolutionary diversification of compound eye and ocelli in insects occurred from an ancestral visual organ around 500 million years ago. Concurrently, opsin genes were also duplicated to provide distinct spectral sensitivities to different PRs of compound eye and ocelli. In the fruit fly Drosophila melanogaster, Rhodopsin1 (Rh1) and Rh2 are closely related opsins that are originated from the duplication of a single ancestral gene. However, in the visual organs, Rh2 is uniquely expressed in ocelli whereas Rh1 is uniquely expressed in outer PRs of the compound eye. It is currently unknown how this differential expression of Rh1 and Rh2 in the two visual organs is controlled to provide unique spectral sensitivities to ocelli and compound eyes. Here, we show that Homothorax (Hth) is expressed in ocelli and confers proper rhodopsin expression. We find that Hth controls a binary Rhodopsin switch in ocelli to promote Rh2 expression and repress Rh1 expression. Genetic and molecular analysis of rh1 and rh2 supports that Hth acts through their promoters to regulate Rhodopsin expression in the ocelli. Finally, we also show that when ectopically expressed in the retina, hth is sufficient to induce Rh2 expression only at the outer PRs in a cell autonomous manner. We therefore propose that the diversification of rhodpsins in the ocelli and retinal outer PRs occurred by duplication of an ancestral gene, which is under the control of Homothorax.

genetics↗

bioRxiv2020

Multimodal and multisensory coding in the Drosophila larval peripheral gustatory center

The ability to evaluate food palatability is innate in all animals, ensuring their survival. The external taste organ in Drosophila larvae is composed of only few sensory neurons but enables discrimination between a wide range of chemicals and displays high complexity in receptor gene expression and physiological response profile. It remains largely unknown how the discrepancy between a small neuronal number and the perception of a large sensory space is genetically and physiologically resolved. We tackled dissection of taste sensory coding at organ level with cellular resolution in the fruit fly larva by combining whole-organ calcium imaging and single-cell transcriptomics to map physiological properties and molecular features of individual neurons. About one third of gustatory sense neurons responded to multiple tastants, showing a rather large degree of multimodality within the taste organ. Further supporting the notion of signal integration at the periphery, we observed neuronal deactivation events within simultaneous neighboring responses, suggesting inter-cellular communication through electrical coupling and thus providing an additional level in how neurons may encode taste sensing. Interestingly, we identified neurons responding to both mechanical and taste stimulation, indicating potential multisensory integration. On a molecular level, chemosensory cells show heterogeneity in neuromodulator expression. In addition to a broad cholinergic profile, markers on dopaminergic, glutamatergic or neuropeptidergic pathways are present either in distinct cell populations or are seemingly co-expressed. Our data further extend the sensory capacity of the larval taste system pointing towards an unanticipated degree of multimodal and multisensory coding principles.

neuroscience↗

bioRxiv2019

Temporal control of inhibition via muscarinic acetylcholine receptor signaling generates ON and OFF selectivity in a simple visual circuit

ON and OFF selectivity in visual processing is encoded by parallel pathways that respond to either increments or decrements of light. Despite lacking anatomical features to support split channels, Drosophila larvae effectively perform visually-guided behaviors. To understand principles guiding visual computation in this simple circuit, we focus on the physiological properties and behavioral relevance of larval visual interneurons and elucidate their functions in visual processing. We find that the ON vs. OFF discrimination in the larval visual circuit emerges through light-elicited cholinergic signaling that depolarizes the cholinergic interneuron (cha-lOLP) and hyperpolarizes the glutamatergic interneuron (glu-lOLP). Genetic studies further indicate that muscarinic acetylcholine receptor (mAchR)/Go signaling in glu-lOLP separates the ON and OFF signals through temporal delays, the disruption of which strongly impacts both physiological responses of downstream projection neurons and dark-induced pausing behavior. Together, our studies identify cellular and molecular substrates for OFF detection in the larval visual circuit and suggests temporal control of inhibition functions as an effective strategy in generating ON and OFF selectivity without anatomical segregation.

neuroscience↗

bioRxiv2018

Glass confers rhabdomeric photoreceptor identity in Drosophila, but not across all metazoans

Across metazoans, visual systems employ different types of photoreceptor neurons to detect light. These include rhabdomeric PRs, which exist in distantly related phyla and possess an evolutionarily conserved phototransduction cascade. While the development of rhabdomeric PRs has been thoroughly studied in the fruit fly Drosophila melanogaster, we still know very little about how they form in other species. To investigate this question, we tested whether the transcription factor Glass, which is crucial for instructing rhabdomeric PR formation in Drosophila, may play a similar role in other metazoans. Glass homologues exist throughout the animal kingdom, indicating that this protein evolved prior to the metazoan radiation. Interestingly, our work indicates that glass is not expressed in rhabdomeric photoreceptors in the planarian Schmidtea mediterranea nor in the annelid Platynereis dumerilii. Combined with a comparative analysis of the Glass DNA-binding domain, our data suggest that the fate of rhabdomeric PRs is controlled by Glass-dependent and Glass-independent mechanisms in different animal clades.

developmental biology↗

bioRxiv2018

An expression atlas of chemosensory ionotropic glutamate receptors identifies a molecular basis of carbonation detection

Taste perception is thought to involve the encoding of appetitive and aversive chemical cues in food through a limited number of sensory pathways. Through expression analysis of the complete repertoire of Drosophila Ionotropic Receptors (IRs), a sensory subfamily of ionotropic glutamate receptors, we reveal that the majority of IRs is expressed in diverse peripheral neuron populations across gustatory organs in both larvae and adults, implying numerous roles in taste-evoked behaviours. We characterise Ir56d, which labels two anatomically-distinct classes of neurons in the proboscis: one represents a subset of sugar- and fatty acid-sensing neurons, while the other responds to carbonated solutions and fatty acids. Mutational analysis shows that IR56d, together with the broadly-expressed co-receptors IR25a and IR76b, is essential for physiological activation by carbonation and fatty acids, but not sucrose. We further demonstrate that carbonation is behaviourally attractive to flies (in an IR56d-dependent manner), but in a distinct way to other appetitive stimuli. Our work provides a valuable toolkit for investigating the taste functions of IRs, defines a molecular basis of carbonation sensing, and illustrates how the gustatory system uses combinatorial expression of sensory receptors in distinct neuron types to coordinate behaviour.

neuroscience↗

bioRxiv2017

CHARACTERIZATION OF THE bHLH FAMILY OF TRANSCRIPTIONAL REGULATORS IN THE ACOEL S. roscoffensis AND THEIR PUTATIVE ROLE IN NEUROGENESIS

BackgroundThe basic Helix loop helix (bHLH) family of transcription factors is one of the largest superfamilies of regulatory transcription factors and are widely used in eukaryotic organisms. They play an essential role in a range of metabolic, physiological, and developmental processes, including the development of the nervous system (NS). These transcription factors have been studied in many metazoans, especially in vertebrates but also in early branching metazoan clades such as the cnidarians and sponges. However, currently very little is known about their expression in the most basally branching bilaterian group, the xenacoelomorphs. Recently, our laboratory has characterized the full complement of bHLH in the genome of two members of the Xenacoelomorpha, the xenoturbellid Xenoturbella bocki and the acoel Symsagittifera roscoffensis. Understanding the patterns of bHLH gene expression in members of this phylum (in space and time) provides critical new insights into the conserved roles of the bHLH and their putative specificities in this group. Our focus is on deciphering the specific roles that these genes have in the process of neurogenesis.\n\nResultsHere, we analyze the developmental expression of the whole complement of bHLH genes identified in the acoel S. roscoffensis. Based on their expression patterns several members of bHLH class A appear to have specific conserved roles in neurogenesis, while other class A genes (as well as members of other classes) have likely taken on more generalized functions. All gene expression patterns are described in embryos and early juveniles.\n\nConclusionOur results suggest that the main roles of the bHLH genes of S. roscoffensis are evolutionarily conserved, with a specific subset dedicated to patterning the nervous system: SrAscA, SrAscB, SrHes/Hey, SrNscl, SrSrebp, SrE12/E47 and SrOlig.

developmental biology↗