Biology subjects

Witvliet, D.

Publications and source records attributed to Witvliet, D..

5 recordsLinked to original sources

bioRxiv2022

Post-embryonic maturation of the C. elegans motor circuit

During development, animals can maintain behavioral output even as the underlying circuits structurally remodel. After hatching, C. elegans undergoes substantial motor neuron expansion and synapse re-wiring while the animal continuously moves with an undulatory pattern. To understand how the circuit transitions from its juvenile to mature configuration without disrupting functional output, we reconstructed the C. elegans motor circuit by electron microscopy across larval development. We observed: 1) Embryonic motor neurons transiently interact with the developing post-embryonic motor neurons prior to remodeling of their juvenile wiring; 2) Post-embryonic neurons initiate synapse development with their future partners as their neurites navigate through the juvenile nerve cords; 3) Embryonic and post-embryonic neurons sequentially build structural machinery needed for the adult circuit before the embryonic neurons relinquish their roles to post-embryonic neurons; 4) This transition is repeated region by region along the body in an anterior to posterior sequence, following the birth order of post-embryonic neurons. Through this orchestrated, programmed and gradual rewiring, the motor circuit transforms from asymmetric to symmetric wiring. These maturation strategies support the continuous maintenance of motor patterns as the juvenile circuit develops into the adult configuration. HighlightsO_LIPost-embryonic motor circuit maturation was reconstructed by synapse-resolution serial EM. C_LIO_LIMotor patterns are maintained as the circuit matures from asymmetric to symmetric configuration. C_LIO_LIProgrammed rewiring gradually and sequentially transforms the circuit structure. C_LIO_LIPreparatory and communicative wiring-rewiring allows maturation without functional disruption. C_LI

neuroscience↗

bioRxiv2021

Extrasynaptic signaling enables an asymmetric juvenile motor circuit to produce a symmetric mature gait.

In many animals, there is a direct correspondence between the motor patterns that drive locomotion and the motor neuron innervation onto the muscle groups. For example, the adult C. elegans moves with symmetric and alternating dorsal-ventral bending waves arising from symmetric motor neuron input onto the dorsal and ventral muscles. In contrast to the adult, the C. elegans motor circuit at the juvenile larval stage has asymmetric wiring between motor neurons and muscles, but still generates adult-like bending waves with dorsal-ventral symmetry. We show that in the juvenile circuit, wiring between excitatory and inhibitory motor neurons coordinates the contraction of dorsal muscles with relaxation of ventral muscles, producing dorsal bends. However, ventral bending is not driven by analogous wiring. Instead, ventral muscles are excited uniformly by premotor interneurons through extrasynaptic signaling. Ventral bends occur in anti-phasic entrainment to activity of the same motor neurons that drive dorsal bends. During maturation, the juvenile motor circuit is replaced by two motor subcircuits that separately drive dorsal and ventral bending. Modeling reveals that the juveniles immature motor circuit is an adequate solution to generate adult-like dorsal-ventral bending before the animal matures. Developmental rewiring between functionally degenerate circuit solutions, that both generate symmetric bending patterns, minimizes behavioral disruption across maturation. HighlightsO_LIC. elegans larvae generate symmetric motor pattern with an asymmetrically wired motor circuit. C_LIO_LISynaptic wiring between excitatory and inhibitory motor neurons drives dorsal bending. C_LIO_LIExtrasynaptic excitation by premotor interneurons entrains ventral muscles for anti-phasic ventral bending. C_LIO_LIA developmental strategy to enable mature motor pattern before the circuit structurally matures. C_LI

neuroscience↗

bioRxiv2021

Structural analysis of the C. elegans dauer larval anterior sensilla by Focused Ion Beam-Scanning Electron Microscopy

At the end of the first larval stage, the nematode Caenorhabditis elegans developing in harsh environmental conditions is able to choose an alternative developmental path called the dauer diapause. Dauer larvae exhibit different physiology and behaviors from non-dauer larvae. Using focused ion beam scanning electron microscopy (FIB-SEM), we volumetrically reconstructed the anterior sensory apparatus of C. elegans dauer larvae with unprecedented precision. We provide a detailed description of some neurons, focusing on structural details that were unknown or unresolved by previously published studies. They include: 1) dauer-specific branches of the IL2 sensory neurons project into the periphery of anterior sensilla and motor or putative sensory neurons at the sub-lateral cords; 2) ciliated endings of URX sensory neurons are supported by both ILso and AMso socket cells near the amphid openings; 3) variability in amphid sensory dendrites among dauers; 4) somatic RIP interneurons maintain their projection into the pharyngeal nervous system. Our results support the notion that dauer larvae structurally expand their sensory system to facilitate searching for more favorable environments.

neuroscience↗

bioRxiv2020

Natural sensory context drives diverse brain-wide activity during C. elegans mating

Natural goal-directed behaviors often involve complex sequences of many stimulus-triggered components. Understanding how brain circuits organize such behaviors requires mapping the interactions between an animal, its environment, and its nervous system. Here, we use continuous brain-wide neuronal imaging to study the full performance of mating by the C. elegans male. We show that as each mating unfolds in its own sequence of component behaviors, the brain operates similarly between instances of each component, but distinctly between different components. When the full sensory and behavioral context is taken into account, unique roles emerge for each neuron. Functional correlations between neurons are not fixed, but change with behavioral dynamics. From the contribution of individual neurons to circuits, our study shows how diverse brain-wide dynamics emerge from the integration of sensory perception and motor actions within their natural context.

neuroscience↗

bioRxiv2020

Connectomes across development reveal principles of brain maturation in C. elegans

From birth to adulthood, an animals nervous system changes as its body grows and its behaviours mature. The form and extent of circuit remodelling across the connectome is unknown. We used serial-section electron microscopy to reconstruct the full brain of eight isogenic C. elegans individuals across postnatal stages to learn how it changes with age. The overall geometry of the brain is preserved from birth to adulthood. Upon this constant scaffold, substantial changes in chemical synaptic connectivity emerge. Comparing connectomes among individuals reveals substantial connectivity differences that make each brain partly unique. Comparing connectomes across maturation reveals consistent wiring changes between different neurons. These changes alter the strength of existing connections and create new connections. Collective changes in the network alter information processing. Over development, the central decision-making circuitry is maintained whereas sensory and motor pathways substantially remodel. With age, the brain progressively becomes more feedforward and discernibly modular. Developmental connectomics reveals principles that underlie brain maturation.

neuroscience↗