Biology subjects

Schneider, A. C.

Publications and source records attributed to Schneider, A. C..

10 recordsLinked to original sources

bioRxiv2026

Disrupting the clock of the Madeira cockroach through RNAi-mediated knockdown of CLOCK and CYCLE

1Endogenous circadian clocks control circadian rhythms in physiology and behavior. The predominant hypothesis of biological timing suggests that the responsible master clock for all endogenous circadian rhythms is constituted by an evolutionary conserved transcriptional-translational feedback loop (TTFL) clock consisting of positive feedforward and negative feedback elements. Unexpectedly, in contrast to the evolutionary derived insect Drosophila, RNAi-dependent knockdown of any of the negative feedback elements of the core TTFL clock in the basal Madeira cockroach Rhyparobia maderae does not delete circadian rhythms in locomotor activity. Shown here, neither RNAi-dependent triple knockdowns of all three negative feedback elements PERIOD, TIMELESS1, and CRYPTOCHROME2, nor single and double knockdown of the positive elements CLOCK and CYCLE did directly delete circadian locomotor rhythms as mRNA levels declined. Thus, our experimental data indicates the presence of compensatory elements, likely through posttranslational feedback loop (PTFL) controlled modifications. To explore alternative mechanisms, we constructed a computational model of a neuronal circadian pacemaker network using a network of coupled limit cycle oscillators, specifically planar switching affine systems (PSAS). The PSAS model comprises plasma membrane-associated PTFL clocks that are coupled to the TTFL nuclear clocks. Modeling results aligned with our experimental results. Therefore, both our experimental and modeling data support a systemic hypothesis of biological timing. 3 Significance statementBased mostly upon genetic studies in derived taxa like Drosophila it is hypothesized that circadian timing of behavior is strictly controlled by specific circadian clock neurons in the brain, realized through a transcriptional-translational feedback loop (TTFL) clock. In contrast to this common hierarchical model that requires transcription, we provide first evidence in a basal taxon - the Madeira cockroach - for a systemic explanation of circadian timing of behavior that is based on coupled TTFL and posttranslational feedback loop (PTFL) clocks in adaptive neuronal networks.

physiology↗

bioRxiv2025

Strain-level diversity of giant viruses infecting chlorarachniophyte algae in the subtropical North Pacific

Giant DNA viruses are ubiquitous among unicellular eukaryotes and occur in marine, freshwater, and terrestrial environments. Despite intense metagenomic data mining, their strain-level diversity remains largely unexplored. Here we introduce a model system comprising four isolates of a giant virus called ChlorV, which infects marine microalgae of the class Chlorarachniophyceae (Rhizaria) from station ALOHA, Hawaii. The ChlorV genomes are 469 kbp to 493 kbp long and encode approximately 400 proteins, at least 106 of which are present n purified virions. Although the four viral genomes are highly syntenic, they differ by several insertions and deletions that often encode methyltransferases. Interestingly, we found that some of these methyltransferase genes correlated with specific DNA methylation patterns in the ChlorV strain Our study describes the first giant viruses infecting the eukaryotic supergroup Rhizaria and demonstrates how viral strain-level variation in gene content and epigenetic features may affect eco-evolutionary processes in marine microalgae.

microbiology↗

bioRxiv2025

Orco regulates the circadian activity of pheromone-sensitive olfactory receptor neurons in hawkmoths

1The mating behavior of nocturnal Manduca sexta hawkmoths is under strict temporal control. It is orchestrated via circadian and ultradian oscillations in sex-pheromone stimuli as social Zeitgeber. The extremely sensitive pheromone-detecting olfactory receptor neurons (ORNs) that innervate the long trichoid sensilla on the males antennae are peripheral circadian clocks. They express the transcriptional-translational feedback loop (TTFL) circadian clockwork, best characterized in Drosophila melanogaster. In hawkmoths, it is still unknown whether or how the ORN TTFL clockwork regulates the daily rhythms in pheromone sensitivity and in temporal resolution of ultradian pheromone pulses as prerequisites to the temporal regulation of hawkmoth mating behavior. We hypothesize that, rather than the slow TTFL clock, a more rapidly adaptive post-translational feedback loop (PTFL) clockwork, assembled in a signalosome in the ORN plasma membrane, allows for temporal control of pheromone detection via generation of multiscale endogenous membrane potential oscillations. The potential oscillations of the PTFL clock could rapidly synchronize to oscillations of pheromone stimuli at different time scales, thus enabling the prediction of stimulus patterns as a mechanism for active sensing. With in vivo long-term tip recordings of long trichoid sensilla of male hawkmoths, we analyzed the spontaneous spiking activity indicative of the ORNs endogenous membrane potential oscillations. Consistent with our hypothesis of a multiscale PTFL clock in hawkmoth ORNs, spontaneous spiking was modulated on ultradian and circadian time scales, with maximum activity at night. When we blocked the evolutionarily conserved olfactory receptor coreceptor (Orco), the circadian modulation was abolished but the ultradian frequency modulation of the spontaneous activity remained. Consistent with PTFL control, Orco was not under the transcriptional control of the TTFL clock, but its modulation of spontaneous spiking activity was dependent on cAMP. We could replicate the experimental data in a conductance-based computational model of an ORN. In this model, Orco conductance changed as a function of fluctuating 2nd messenger levels. This study demonstrates that a PTFL clock is sufficient to impose a circadian pattern on ORN sensitivity. Future experiments are necessary to further challenge our novel hypothesis. 2. Significance statementIt is generally assumed that all circadian rhythms in an organism are driven by a transcriptional-translational feedback loop (TTFL) clock. In this study, we demonstrate with in vivo recordings of hawkmoth pheromone-sensitive olfactory receptor neurons (ORNs) that the olfactory receptor coreceptor (Orco) is the key pacemaker channel for controlling circadian rhythms in spontaneous spiking activity. Since Orco expression is not driven by the TTFL clock, we put forward the novel hypothesis that Orco is a core element of a post-translational feedback loop (PTFL) membrane clock assembled in a signalosome controlling interlinked oscillations in 2nd messengers and membrane potential. Accordingly, our computational model predicts that ORN sensitivity is tuned by circadian changes in the conductance of an Orco ion channel, which is mediated by cycling levels of cyclic nucleotides. Our novel hypothesis that highlights the contribution of feedback-controlled post-translational modifications to the generation of endogenous circadian rhythmicity should spark further challenges.

physiology↗

bioRxiv2024

Hawkmoth pheromone transduction involves G protein-dependent phospholipase Cβ signaling

1Evolutionary pressures adapted insect chemosensation to the respective insects physiological needs and tasks in their ecological niches. Solitary nocturnal moths rely on their acute olfactory sense to find mates at night. Pheromones are detected with maximized sensitivity and high temporal resolution through mechanisms that are mostly unknown. While the inverse topology of insect olfactory receptors and heteromerization with the coreceptor Orco suggest ionotropic transduction via odorant-gated receptor-ion channel complexes, contradictory data propose amplifying G protein-coupled transduction. Here, we used in vivo tip-recordings of pheromone-sensitive sensilla of male Manduca sexta hawkmoths at specific times of day (rest vs. activity). Since the olfactory receptor neurons distinguish signal parameters in three consecutive temporal windows of their pheromone response (phasic; tonic; late, long-lasting), respective response parameters were analyzed separately. Disruption of G protein-coupled transduction and block of phospholipase C decreased and slowed the phasic response component during the activity phase of hawkmoths without affecting any other component of the response during activity and rest. A more targeted disruption of G subunits by blocking Go or sustained activation of Gs using bacterial toxins affected the phasic pheromone response, while toxins targeting Gq and G12/13 were ineffective. Consistent with these data, the expression of phospholipase C{beta}4 depended on zeitgeber time, which indicates circadian clock-modulated metabotropic pheromone transduction cascades that maximize sensitivity and temporal resolution of pheromone transduction during the hawkmoths activity phase. Thus, discrepancies in the literature on insect olfaction may be resolved by considering circadian timing and the distinct odor response components. 2 Significance statementInsect chemosensory transduction is typically thought to be ionotropic, but data from different insect species suggests that metabotropic olfactory signaling may occur, either alongside or instead of ionotropic mechanisms. Nocturnal moths, known for their extraordinarily sensitive pheromone-detecting olfactory receptor neurons, likely use metabotropic signal amplification. To overcome limitations of previous in vitro studies, we conducted tip-recordings of pheromone-sensitive sensilla in healthy hawkmoths at specific zeitgeber times. Disrupting G protein signaling and phospholipase C{beta} reduced sensitivity and altered response kinetics, revealing strict temporal control of transduction. Thus, contradictory findings in insect olfaction may be reconciled by considering diverse evolutionary pressures for distinct chemosensory signals in different species, zeitgeber time, and disparate odor response parameters.

physiology↗

bioRxiv2023

Comodulation reduces interindividual variability of circuit output

2Ionic current levels of identified neurons vary substantially across individual animals. Yet, under similar conditions, neural circuit output can be remarkably similar, as evidenced in many motor systems. All neural circuits are influenced by multiple neuromodulators which provide flexibility to their output. These neuromodulators often overlap in their actions by modulating the same channel type or synapse, yet have neuron-specific actions resulting from distinct receptor expression. Because of this different receptor expression pattern, in the presence of multiple convergent neuromodulators, a common downstream target would be activated more uniformly in circuit neurons across individuals. We therefore propose that a baseline tonic (non-saturating) level of comodulation by convergent neuromodulators can reduce interindividual variability of circuit output. We tested this hypothesis in the pyloric circuit of the crab, Cancer borealis. Multiple excitatory neuropeptides converge to activate the same voltage-gated current in this circuit, but different subsets of pyloric neurons have receptors for each peptide. We quantified the interindividual variability of the unmodulated pyloric circuit output by measuring the activity phases, cycle frequency and intraburst spike number and frequency. We then examined the variability in the presence of different combinations and concentrations of three neuropeptides. We found that at mid-level concentration (30 nM) but not at near-threshold (1 nM) or saturating (1 M) concentrations, comodulation by multiple neuropeptides reduced the circuit output variability. Notably, the interindividual variability of response properties of an isolated neuron was not reduced by comodulation, suggesting that the reduction of output variability may emerge as a network effect. 3 Significance StatementNeuromodulation has been explored as a mechanism to provide flexibility to the output of neural circuits. All neural circuits are subject to neuromodulation by multiple substances. Here, we propose a different but complimentary role for neuromodulation. We use two general facts about neuromodulation to show that convergent comodulation at tonic mid-concentration levels reduces interindividual variability of neural circuit output. These facts are that 1) Multiple neuromodulators can have convergent actions on the same subcellular substrates and 2) Neurons express different neuromodulator receptors at different levels.

neuroscience↗

bioRxiv2023

Neuropeptides with different cellular targets elicit similar output in a central pattern generating circuit

Neuromodulation lends flexibility to neural circuit operation but the general notion that different neuromodulators sculpt neural circuit activity into distinct and characteristic patterns is complicated by interindividual variability. In addition, some neuromodulators converge onto the same signaling pathways, with similar effects on neurons and synapses. We compared the effects of three neuropeptides on the rhythmic pyloric circuit in the crab Cancer borealis stomatogastric nervous system. Proctolin (PROC), crustacean cardioactive peptide (CCAP), and red pigment concentrating hormone (RPCH) all activate the same modulatory inward current, IMI, and have convergent actions on synapses. However, while PROC targets all four neuron types in the core pyloric circuit, CCAP and RPCH target the same subset of only two neurons. After removal of spontaneous neuromodulator release, none of the neuropeptides restored the control cycle frequency, but all restored the relative timing between neuron types. Consequently, differences between neuropeptide effects were mainly found in the spiking activity of different neuron types. We performed statistical comparisons using the Euclidean distance in the multidimensional space of normalized output attributes to obtain a single measure of difference between modulatory states. Across preparations, circuit output in PROC was distinguishable from CCAP and RPCH, but CCAP and RPCH were not distinguishable from each other. However, we argue that even between PROC and the other two neuropeptides, population data overlapped enough to prevent reliable identification of individual output patterns as characteristic for a specific neuropeptide. We confirmed this notion by showing that blind classifications by machine learning algorithms were only moderately successful. Significance StatementIt is commonly assumed that distinct behaviors or circuit activities can be elicited by different neuromodulators. Yet it is unknown to what extent these characteristic actions remain distinct across individuals. We use a well-studied circuit model of neuromodulation to examine the effects of three neuropeptides, each known to produce a distinct activity pattern in controlled studies. We find that, when compared across individuals, the three peptides elicit activity patterns that are either statistically indistinguishable or show too much overlap to be labeled characteristic. We ascribe this to interindividual variability and overlapping subcellular actions of the modulators. Because both factors are common in all neural circuits, these findings have broad significance for understanding the chemical neuromodulatory actions while considering interindividual variability.

neuroscience↗

bioRxiv2022

Unmasking hidden changes in intrinsic properties in neurons that coordinate oscillatory networks

2.Neurons utilize gain control to efficiently encode shifting inputs with maximum sensitivity. While gain control is present in a multitude of neurons, research on the underlying mechanisms is still sparse. We focused on one coordinating neuron (ASCE) in the crayfish swimmeret system that is both necessary and sufficient to coordinate distributed motor circuits. This neuron encodes properties of the motor activity in its home ganglion and sends the information as burst of spikes to its anterior target ganglia. Previous research has shown that ASCE encodes the strength of the motor activity by its spike number, and that the range of the number of spikes per burst adapts to the average motor activity. In turn, the motor activity can be activated and modulated via cholinergic pathways. We explored ASCEs response to changing levels of motor system excitation, which was induced with cholinergic agonists, both when the neuron was part of the full swimmeret systems circuit and when it was isolated from the network. The cholinergic agonist carbachol directly depolarized ASCEs membrane potential via nicotinic receptors when the neuron was isolated. In the intact circuit, ASCEs membrane potential did not change but its input resistance decreased. This indicated an additional indirect action of carbachol, presumably via presynaptic central pattern generating neurons at the core of each motor circuit. The balance of direct and indirect effects could allow ASCE to match its spiking range to the systems excitation level. 1. Summary statementA balance of direct and indirect cholinergic effects precisely controls the membrane potential, and therefore the gain, of a neuron that is involved in the coordination of distributed motor circuits.

neuroscience↗

bioRxiv2021

Mapping circuit dynamics during function and dysfunction

Neural circuits can generate many spike patterns, but only some are functional. The study of how circuits generate and maintain functional dynamics is hindered by a poverty of description of circuit dynamics across functional and dysfunctional states. For example, although the regular oscillation of a central pattern generator is well characterized by its frequency and the phase relationships between its neurons, these metrics are ineffective descriptors of the irregular and aperiodic dynamics that circuits can generate under perturbation or in disease states. By recording the circuit dynamics of the well-studied pyloric circuit in C. borealis, we used statistical features of spike times from neurons in the circuit to visualize the spike patterns generated by this circuit under a variety of conditions. This unsupervised approach captures both the variability of functional rhythms and the diversity of atypical dynamics in a single map. Clusters in the map identify qualitatively different spike patterns hinting at different dynamical states in the circuit. State probability and the statistics of the transitions between states varied with environmental perturbations, removal of descending neuromodulation, and the addition of exogenous neuromodulators. This analysis reveals strong mechanistically interpretable links between complex changes in the collective behavior of a neural circuit and specific experimental manipulations, and can constrain hypotheses of how circuits generate functional dynamics despite variability in circuit architecture and environmental perturbations.

neuroscience↗

bioRxiv2019

The bacterial microbiota of a parasitic plant and its host

How plant-associated microbiota are shaped by, and potentially contribute to the unique ecology and heterotrophic life history of parasitic plants is relatively unknown. Here, we investigate the leaf and root bacterial communities associated with the root holoparasite Orobanche hederae and its host plant Hedera spp. We sequenced the V4 region of the 16S rRNA gene from DNA extracted from leaf and root samples of naturally growing populations of Orobanche and infected and uninfected Hedera. Root bacteria inhabiting Orobanche were less diverse, had fewer co-associations, and displayed increased compositional similarity to leaf bacteria relative to Hedera. Overall, Orobanche bacteria exhibited significant congruency with Hedera root bacteria across sites, but not the surrounding soil. Infection had localized and systemic effects on Hedera bacteria, which included effects on the abundance of individual taxa and root network properties. Collectively, our results indicate that the parasitic plant microbiome is derived but distinct from host plant microbiota, exhibits increased homogenization between shoot and root tissues, and displays far fewer co-associations among individual bacterial members. Host plant infection is accompanied by modest changes of associated microbiota at both local and systemic scales compared with uninfected individuals. Our results provide insight into the assembly and function of plant microbiota.

ecology↗

bioRxiv2018

Adaptive Encoding of Coordinating Information in the Crayfish Central Nervous System

Locomotion is essential for an animals survival. This behavior can range from directional changes to adapting the motor force to the conditions of its surroundings. Even if speed and force of movement are changing, the relative coordination between the limbs or body segments has to stay stable in order to provide the necessary thrust. The coordinating information necessary for this task is not always conveyed by sensory pathways. Adaptation is well studied in sensory neurons, but only few studies have addressed if and how coordinating information changes in cases where a local circuit within the central nervous system is responsible for the coordination between body segments at different locomotor activity states.\n\nOne system that does not depend on sensory information to coordinate a chain of coupled oscillators is the swimmeret system of crayfish. Here, the coordination of four coupled CPGs is controlled by central Coordinating Neurons. Cycle by cycle, the Coordinating Neurons encode information about the activity state of their home ganglion as burst of spikes, and send it as corollary discharge to the neighboring ganglia. Activity states, or excitation levels, are variable in both the living animal and isolated nervous system; yet the amount of coordinating spikes per burst is limited.\n\nHere, we demonstrate that the systems excitation level tunes the encoding properties of the Coordinating Neurons. Their ability to adapt to excitation level, and thus encode relative changes in their home ganglions activity states, is mediated by a balancing mechanism. Manipulation of cholinergic pathways directly affected the coordinating neurons electrophysiological properties. Yet, these changes were counteracted by the networks influence. This balancing may be one feature to adapt the limited spike range to the systems current activity state.

neuroscience↗