Biology subjects

Stewart, J. C.

Publications and source records attributed to Stewart, J. C..

6 recordsLinked to original sources

bioRxiv2026

Contextualized phenovectors reveal a Drosophila serotonergic circuit controlling satiety

Distinguishing whether a neural circuit genuinely controls a holistic behavioral state, rather than merely producing isolated effects, is a central challenge in neuroscience. Feeding research illustrates the problem: decades of work have reached conflicting conclusions partly because individual behavioral features are assessed in isolation. Here we establish a contextualized ethomics approach that benchmarks optogenetic circuit manipulations against natural hunger-satiety transitions, using high-dimensional behavioral tracking in Drosophila and starvation as a ground-truth intervention. Applying this framework, we find that serotonergic neurons marked by the Tryptophan hydroxylase neuronal (Trhn) enhancer are both required for and instructive of a satiety-like state, whereas other feeding-related circuits produce only fragmentary behavioral changes. Intersectional dissection localized this control to Trhn neurons of the ventral nerve cord, which act through the sugar transporter Sut2 to sense nutrient state. This work strengthens our understanding of serotonergic feeding control and provides a generalizable framework for validating circuit-state relationships.

neuroscience↗

bioRxiv2026

A mushroom-body output neuron that mediates octopamine-driven and hunger-motivated feeding in Drosophila

Feeding behavior requires the integration of environmental cues, metabolic signals, and internal states through neuromodulatory networks, yet the role of specific neuromodulatory neurons and how they are coordinated in controlling feeding remains unclear. Using automated feed-tracking and optogenetics in Drosophila melanogaster, we found that activation of two octopaminergic neurons (VPM3/4) increases food consumption. Both VPM neurons form direct synapses with a mushroom-body output neuron MBON11, which, through opto-activation and opto-inhibition, can exert bidirectional control over food intake, with sexually dimorphic effects. Epistasis experiments demonstrated that octopamine-driven feeding requires functional MBON11 output. Additionally, we found that the dopaminergic PPL101 neurons, which also synapse with MBON11, are required for hunger-driven feeding. Ethomic analysis contextualized with natural hunger and satiety provided a holistic view of how different neuron types linked to the mushroom-body influence feeding behaviors. This analysis revealed that MBON11 interventions best recapitulate natural hunger-satiety transitions. These findings revealed a circuit where two neuromodulatory neuron types with distinct unidirectional feeding effects--octopaminergic VPM3/4 (instructive but not required) and dopaminergic PPL101 (required but not instructive)--converge onto MBON11, a neuron whose activity is both required for and instructive of hunger-related feeding. This circuit arrangement may represent an architecture for integrating multiple motivational signals in feeding regulation. Key pointsO_LIWhen activated, octopaminergic VPM3 and VPM4 cells drive increased food consumption, effects that require octopamine signaling and are dependent on MBON11 function. C_LIO_LIOctopaminergic neuronal activity is not required for hunger-driven feeding. C_LIO_LIReceiving direct synaptic inputs from VPM3 and 4, MBON11 neurons bidirectionally control feeding, and broadly phenocopy natural hunger-satiety transitions. C_LIO_LIDopaminergic PPL101 neurons that synapse onto MBON11 are required for hunger-motivated feeding. C_LIO_LIMBON11 appears to integrate octopaminergic and dopaminergic signals, and regulate the feeding behavioral state. C_LI

neuroscience↗

bioRxiv2025

Entirely synthetic memory inception via dual optogenetic activation of sensory and dopaminergic neurons

Associative conditioning is a fundamental learning paradigm that links salient stimuli to appropriate behavior. The vinegar fly is an important memory model that can associate odors with rewarding or punishing reinforcement stimuli via distinct sets of dopaminergic neurons. While much is known about learning, a crucial question remains: is the simple co-activation of sensory and neuromodulatory dopaminergic neurons sufficient to induce memory formation? To address this, we systematically replaced natural stimuli, namely odor-evoked activity, punishment, and reward signals, with optogenetic activation of corresponding neurons, both individually and in combination. In all cases, including a full-substitution paradigm where both olfactory activity and reinforcement dopamine signals were replaced, optogenetic activation successfully implanted synthetic memories. These findings provide a clear answer: simple coincident, rectangular-pulse sensory and neuromodulatory stimulation can instruct associative memory formation. We conclude that associative memory does not have strict requirements for temporal or ensemble activity patterns in olfactory or dopaminergic neurons that are specific to natural stimuli (e.g. odorants, sugar, or pain); rather, simple coincidence is an effective driver of memory inception. These findings open new avenues for manipulating and studying memory formation with all-optical control.

animal behavior and cognition↗

bioRxiv2022

A dopaminergic memory circuit controls acute valence

The brain must guide immediate responses to beneficial and harmful stimuli while simultaneously writing memories for future reference. While both immediate actions and reinforcement learning are instructed by dopamine, how dopaminergic systems maintain coherence between these two reward functions is unknown. Through optogenetic activation experiments, we showed that the dopamine neurons that inform olfactory memory in Drosophila have a distinct, parallel function driving attraction and aversion (valence). Sensory neurons required for olfactory memory were dispensable to dopaminergic valence. A broadly projecting set of dopaminergic cells had valence that was dependent on dopamine, glutamate, and octopamine. Similarly, a more restricted dopaminergic cluster with attractive valence was reliant on dopamine and glutamate; flies avoided opto-inhibition of this narrow subset, indicating the role of this cluster in controlling ongoing behavior. Dopamine valence was distinct from output-neuron opto-valence in locomotor pattern, strength, and polarity. Overall our data suggest that dopamines acute effect on valence provides a mechanism by which a dopaminergic system can coherently write memories to influence future responses while guiding immediate attraction and aversion.

animal behavior and cognition↗

bioRxiv2018

Automated leg tracking reveals distinct conserved gait and tremor signatures in Drosophila models of Parkinson’s Disease and Spinocerebellar ataxia 3

Genetic models in Drosophila have made invaluable contributions to our understanding of the molecular mechanisms underlying neurodegeneration. In human patients, some neurodegenerative diseases lead to characteristic movement dysfunctions, such as abnormal gait and tremors. However, it is currently unknown whether similar movement defects occur in the respective fly models, which could be used to model and better understand the pathophysiology of movement disorders. To address this question, we developed a machine-learning image-analysis programme -- Feature Learning-based LImb segmentation and Tracking (FLLIT) -- that automatically tracks leg claw positions of freely moving flies recorded on high-speed video, generating a series of body and leg movement parameters. Of note, FLLIT requires no user input for learning. We used FLLIT to characterise fly models of Parkinsons Disease (PD) and Spinocerebellar ataxia 3 (SCA3). Between these models, walking gait and tremor characteristics differed markedly, and recapitulated signatures of the respective human diseases. Selective expression of mutant SCA3 in dopaminergic neurons led to phenotypes resembling that of PD flies, suggesting that the behavioural phenotype may depend on the circuits affected, rather than the specific nature of the mutation. Different mutations produced tremors in distinct leg pairs, indicating that different motor circuits are affected. Almost 190,000 video frames were tracked in this study, allowing, for the first time, high-throughput analysis of gait and tremor features in Drosophila mutants. As an efficient assay of mutant gait and tremor features in an important model system, FLLIT will enable the analysis of the neurogenetic mechanisms that underlie movement disorders.

neuroscience↗

bioRxiv2018

PBRM1 regulates stress response in epithelial cells

Polybromo1 (PBRM1) is a chromatin remodeler subunit highly mutated in cancer, particularly renal clear cell carcinoma. PBRM1 is a member of the SWI/SNF subcomplex, PBAF (PBRM1-Brg1/Brm Associated Factors) and is characterized by six tandem bromodomains. Here we establish a role for PBRM1 in epithelial cell maintenance through the expression of genes involved in cell adhesion, metabolism, stress response, and apoptosis. In support of a general role for PBRM1 in stress response and apoptosis, we observe that loss of PBRM1 results in an increase in reactive oxygen species generation and a decrease in cellular viability under stress conditions. We find that loss of PBRM1 promotes cell growth under favorable conditions but is required for cell survival under conditions of cellular stress.

cell biology↗