Biology subjects

Fily, Y.

Publications and source records attributed to Fily, Y..

9 recordsLinked to original sources

bioRxiv2025

Optimal Neuromuscular Performance Requires Motor Neuron Phosphagen Kinases

Phosphagen systems are crucial for muscle bioenergetics - rapidly regenerating ATP to support the high metabolic demands of intense musculoskeletal activity. However, their roles in motor neurons that drive muscle contraction have received little attention. Here, we knocked down expression of the primary phosphagen kinase [Arginine Kinase 1; ArgK1] in Drosophila larval motor neurons and assessed the impact on presynaptic energy metabolism and neurotransmission in situ. Fluorescent metabolic probes showed a deficit in presynaptic energy metabolism and some glycolytic compensation. Glycolytic compensation was revealed through a faster elevation in lactate at high firing frequencies, and the accumulation of pyruvate subsequent to firing. Our performance assays included two tests of endurance: enforced cycles of presynaptic calcium pumping, and, separately, enforced body-wall contractions for extended periods. Neither test of endurance revealed deficits when ArgK1 was knocked down. The only performance deficits were detected at firing frequencies that approached, or exceeded, twice the firing frequencies recorded during fictive locomotion, where both electrophysiology and SynaptopHluorin imaging showed an inability to sustain neurotransmitter release. Our computational modeling of presynaptic bioenergetics indicates that the phosphagen systems contribution to motor neuron performance is likely through the removal of ADP in microdomains close to sites of ATP hydrolysis, rather than the provision of a deeper reservoir of ATP. Taken together, these data demonstrate that, as in muscle fibers, motor neurons rely on phosphagen systems during activity that imposes intense energetic demands.

neuroscience↗

bioRxiv2024

Mutations in the albinism gene oca2 alter vision-dependent prey capture behavior in the Mexican tetra

Understanding the phenotypic consequences of naturally occurring genetic changes, as well as their impact on fitness, is fundamental to understanding how organisms adapt to an environment. This is critical when genetic variants have pleiotropic effects, as determining how each phenotype impacted by a gene contributes to fitness is essential to understand how and why traits have evolved. A striking example of a pleiotropic gene contributing to trait evolution is the oca2 gene, coding mutations in which underlie albinism and reductions of sleep in the blind Mexican cavefish, Astyanax mexicanus. Here, we characterize the effects of mutations in the oca2 gene on larval prey capture. We find that when conspecific surface fish with engineered mutations in the oca2 allele are hunting, they use cave-like, wide angle strikes to capture prey. However, unlike cavefish or surface fish in the dark, which rely on lateral line mediated hunting, oca2 mutant surface fish use vision when striking at prey from wide angles. Finally, we find that while oca2 mutant surface fish do not outcompete pigmented surface siblings in the dark, pigmented fish outcompete albino fish in the light. This raises the possibility that albinism is detrimental to larval feeding in a surface-like lighted environment, but does not have negative consequences for fish in cave-like, dark environments. Together, these results demonstrate that oca2 plays a role in larval feeding behavior in A. mexicanus. Further, they expand our understanding of the pleiotropic phenotypic consequences of oca2 in cavefish evolution.

animal behavior and cognition↗

bioRxiv2023

Ultrastructural analysis reveals mitochondrial placement independent of synapse placement in fine caliber C. elegans neurons

Neurons rely on mitochondria for an efficient supply of ATP and other metabolites. However, while neurons are highly elongated, mitochondria are discrete and limited in number. Due to the slow rates of diffusion over long distances it follows that neurons would benefit from an ability to control the distribution of mitochondria to sites of high metabolic activity, such as synapses. It is assumed that neurons possess this capacity, but ultrastructural data over substantial portions of a neurons extent that would allow for tests of such hypotheses are scarce. Here, we mined the Caenorhabditis elegans electron micrographs of John White and Sydney Brenner and found systematic differences in average mitochondrial length (ranging from 1.3 to 2.4 m), volume density (3.7% to 6.5%) and diameter (0.18 to 0.24 m) between neurons of different neurotransmitter type and function, but found limited differences in mitochondrial morphometrics between axons and dendrites of the same neurons. Analyses of distance intervals found mitochondria to be distributed randomly with respect to presynaptic specializations, and an indication that mitochondria were displaced from postsynaptic specializations. Presynaptic specializations were primarily localized to varicosities, but mitochondria were no more likely to be found in synaptic varicosities than non-synaptic varicosities. Consistently, mitochondrial volume density was no greater in varicosities with synapses. Therefore, beyond the capacity to disperse mitochondria throughout their length, at least in C. elegans, fine caliber neurons manifest limited sub-cellular control of mitochondrial size and distribution. SIGNIFICANCEBrain function is unequivocally reliant on mitochondrial function for its energy needs, and the mechanisms that cells use to control these organelles is an active field of enquiry. WormImage, a decades old electron microscopy database in the public domain, contains information about the ultrastructural disposition of mitochondria within the nervous system of C elegans over previously unexamined extents. In a largely remote format, a team of students mined this database over the course of the pandemic. They found differences in mitochondrial size and density between neurons, but limited differences between different compartments of the same neurons. Also, while neurons are clearly able to disperse mitochondria throughout their extent, they found little evidence that they "install" mitochondria at synaptic varicosities.

neuroscience↗

bioRxiv2023

Changes in local interaction rules during ontogeny underlie the evolution of collective behavior

Collective motion emerges from individual interactions which produce groupwide patterns in behavior. While adaptive changes to collective motion are observed across animal species, how local interactions change when these collective behaviors evolve is poorly understood. Here, we use the Mexican tetra, A. mexicanus, which exists as a schooling surface form and a non-schooling cave form, to study differences in how fish alter their swimming in response to neighbors across ontogeny and between evolutionarily diverged populations. We find that surface fish undergo a transition to schooling during development that occurs through increases in inter-individual alignment and attraction mediated by changes in the way fish modulate speed and turning relative to neighbors. Cavefish, which have evolved loss of schooling, exhibit neither of these schooling-promoting interactions at any stage of development. These results reveal how evolution alters local interaction rules to produce striking differences in collective behavior.

evolutionary biology↗

bioRxiv2022

Mitochondrial phosphagen kinases support the volatile power demands of motor nerve terminals

Neural function relies on cellular energy supplies meeting the episodic demands of synaptic activity, but little is known about the extent to which power demands (energy demands per unit time) fluctuate, or the mechanisms that match supply with demand. Here, in individually-identified glutamatergic motor neuron terminals of Drosophila larvae, we leveraged prior macroscopic estimates of energy demand to generate profiles of power demand from one action potential to the next. These profiles show that signaling demands can exceed non-signaling demands 10-fold within milliseconds, and terminals with the greatest fluctuation (volatility) in power demand have the greatest mitochondrial volume and packing density. We elaborated on this quantitative approach to simulate adenosine triphosphate (ATP) levels during activity and drove ATP production as a function of the reciprocal of the energy state, but this canonical feedback mechanism appeared to be unable to prevent ATP depletion during locomotion. Muscle cells possess a phosphagen system to buffer ATP levels but phosphagen systems have not been described for motor nerve terminals. We examined these terminals for evidence of a phosphagen system and found the mitochondria to be heavily decorated with an arginine kinase, the key element of invertebrate phosphagen systems. Similarly, an examination of mouse cholinergic motor nerve terminals found mitochondrial creatine kinases, the vertebrate analogues of arginine kinases. Knock down of arginine kinase in Drosophila resulted in rapid depletion of presynaptic ATP during activity, indicating that, in motor nerve terminals, as in muscle, phosphagen systems play a critical role in matching power supply with demand. SIGNIFICANCEFailure of metabolic processes to supply neurons with energy at an adequate rate can lead to synaptic dysfunction and cell death under pathological conditions. Using a quantitative approach at fruit fly motor nerve terminals we generated the first temporal profiles of presynaptic power demand during locomotor activity. This approach revealed challenges for the known mechanisms that match cellular power supply to demand. However, we discovered that motor nerve terminals in fruit flies and mice alike are supported by phosphagen systems, more commonly seen in muscles where they store energy and buffer mismatch between power supply and demand. This study highlights an understudied aspect of neuronal bioenergetics which may represent a bulwark against the progression of some neuropathologies.

neuroscience↗

bioRxiv2021

Characterizing the genetic basis of trait evolution in the Mexican cavefish

Evolution in response to a change in ecology often coincides with various morphological, physiological, and behavioral traits. For most organisms little is known about the genetic and functional relationship between evolutionarily derived traits, representing a critical gap in our understanding of adaptation The Mexican tetra, Astyanax mexicanus, consists of largely independent populations of fish that inhabit at least 30 caves in Northeast Mexico, and a surface fish population, that inhabits the rivers of Mexico and Southern Texas. The recent application of molecular genetic approaches combined with behavioral phenotyping have established A. mexicanus as a model for studying the evolution of complex traits. Cave populations of A. mexicanus are interfertile with surface populations and have evolved numerous traits including eye degeneration, insomnia, albinism and enhanced mechanosensory function. The interfertility of different populations from the same species provides a unique opportunity to define the genetic relationship between evolved traits and assess the co-evolution of behavioral and morphological traits with one another. To define the relationships between morphological and behavioral traits, we developed a pipeline to test individual fish for multiple traits. This pipeline confirmed differences in locomotor activity, prey capture, and startle reflex between surface and cavefish populations. To measure the relationship between traits, individual F2 hybrid fish were characterized for locomotor behavior, prey-capture behavior, startle reflex and morphological attributes. Analysis revealed an association between body length and slower escape reflex, suggesting a trade-off between increased size and predator avoidance in cavefish. Overall, there were few associations between individual behavioral traits, or behavioral and morphological traits, suggesting independent genetic changes underlie the evolution of behavioral and morphological traits. Taken together, this approach provides a novel system to identify genes that underlie naturally occurring genetic variation in morphological and behavioral traits.

evolutionary biology↗

bioRxiv2020

Analysis of social swimming dynamics in the Mexican cavefish

Fish display a remarkable diversity of social behaviors, from highly social to largely solitary. While social behaviors are likely critical for survival, surprisingly little is known about how they evolve in response to changing environmental pressures. With its highly social surface form and multiple populations of a largely asocial, blind, cave-dwelling form, the Mexican tetra, Astyanax mexicanus, provides a powerful model to study the evolution of social behavior. Given numerous morphological and behavioral differences between the surface and cave forms, a primary impediment to understanding how this behavior evolved is a lack of computational and statistical approaches that can precisely identify independent aspects of social behavior. Here, we use motion tracking and kinematic analysis to quantify social swimming patterns and argue that the absence of schooling in cavefish is not merely a consequence of their inability to see but rather a genuine behavioral adaptation that impacts the way they explore their cave environment. Surface fish school, maintaining both close proximity and alignment with each other. In the dark, surface fish no longer school, but we show that they still attempt to align and maintain proximity when they find themselves near another fish. Conversely, cavefish exhibit little preference for proximity or alignment, instead actively avoiding each other. Cavefish also slow down when more fish are present in the tank, which neither surface fish in the light or in the dark do. Using data-driven computer simulations, we show that those two traits - active avoidance and collective slowdown - are sufficient to shift the exploration strategy of cavefish from mostly-following-the-walls to exploring-the-entire-tank. Finally, we find that those differences in collective swimming patterns are largely consistent across independently-evolved cave populations, revealing an evolutionary convergence on this emergent social behavior. Author SummaryThe Mexican tetra fish offers a fascinating window into the evolution of schooling behavior. Its ancestral-like surface form is found in the rivers and lakes of Mexico and Texas and is highly social. Over the last million years, A. mexicanus repeatedly evolved a second, largely asocial cave form after colonizing a series of dark, underground caves. Here we use motion tracking technology to compare the collective displacement patterns of four populations and present evidence that the loss of schooling in cave populations (i) is a genuine example of parallel behavioral evolution rather than a mere consequence of not being able to see in the dark and (ii) could constitute a cave-specific exploration strategy.

animal behavior and cognition↗

bioRxiv2019

Cavefish brain atlases reveal functional and anatomical convergence across independently evolved populations

Environmental perturbation can drive the evolution of behavior and associated changes in brain structure and function. The generation of computationally-derived whole-brain atlases have provided insight into neural connectivity associated with behavior in many model systems. However, these approaches have not been used to study the evolution of brain structure in vertebrates. The Mexican tetra, A. mexicanus, comprises river-dwelling surface fish and multiple independently evolved populations of blind cavefish, providing a unique opportunity to identify neuroanatomical and functional differences associated with behavioral evolution. We employed intact brain imaging and image registration on 684 larval fish to generate neuroanatomical atlases of surface fish and three different cave populations. Analyses of brain regions and neural circuits associated with behavioral regulation identified convergence on hypothalamic expansion, as well as changes in transmitter systems including elevated numbers of catecholamine and hypocretin neurons in cavefish populations. To define evolutionarily-derived changes in brain function, we performed whole brain activity mapping associated with feeding and sleep. Feeding evoked neural activity in different sensory processing centers in surface and cavefish. We also identified multiple brain regions with sleep-associated activity across all four populations, including the rostral zone of the hypothalamus and tegmentum. Together, these atlases represent the first comparative brain-wide study of intraspecies variation in a vertebrate model, and provide a resource for studying the neural basis underlying behavioral evolution.

neuroscience↗

bioRxiv2019

Instabilities and Spatiotemporal Dynamics of Active Elastic Filaments

Biological filaments driven by molecular motors tend to experience tangential propulsive forces also known as active follower forces. When such a filament encounters an obstacle, it deforms, which reorients its follower forces and alters its entire motion. If the filament pushes a cargo, the friction on the cargo can be enough to deform the filament, thus affecting the transport properties of the cargo. Motivated by cytoskeletal filament motility assays, we study the dynamic buckling instabilities of a two-dimensional slender elastic filament driven through a dissipative medium by tangential propulsive forces in the presence of obstacles or cargo. We observe two distinct instabilities. When the filaments head is pinned or experiences significant translational but little rotational drag from its cargo, it buckles into a steadily rotating coiled state. When it is clamped or experiences both significant translational and rotational drag from its cargo, it buckles into a periodically beating, overall translating state. Using minimal analytically tractable models, linear stability theory, and fully non-linear computations, we study the onset of each buckling instability, characterize each buckled state, and map out the phase diagram of the system. Finally, we use particle-based Brownian dynamics simulations to show our main results are robust to moderate noise and steric repulsion. Overall, our results provide a unified framework to understand the dynamics of tangentially propelled filaments and filament-cargo assemblies.

biophysics↗