Witvliet, D. et al. (2017) International Worm Meeting "The C. elegans connectome consist of invariant, stochastic, and developmentally regulated synapses."

Berger, D.R., Wang, J., Cook, S.J., Holmyard, D., Lichtman, J.W., Neubauer, M., Laskova, V., Zhen, M., Emmons, S.W., Mulcahy, B., Samuel, A.D.T., Kersen, D., Chisholm, A.D., Schalek, R.L., Koh, W.X., Qian, J., Hall, D.H., Mitchell, J.K., Chang, M., Witvliet, D.

[International Worm Meeting, 2017]

When animals are born, neuronal networks are already in place to integrate sensory cues and effect appropriate behavioral or homeostatic responses. During the course of postnatal development, synapses and circuits undergo refinement and remodeling, updating or adapting sensorimotor behaviors. Rules for developmental remodeling are poorly characterized, because a circuit-level analyses at multiple time points, in multiple animals are missing. We use an isogenic C. elegans N2 population to examine how the neural circuit changes during development. At birth, C. elegans has 218 neurons (excluding CAN); 82 new neurons are incorporated into the nervous system before the end of larval development. These include sensory, motor, and interneurons that are located throughout the body, suggesting a system-wide modification of the juvenile circuit during post-embryonic development. Using serial-section electron microscopy, we mapped the synaptic connectivity in the head and tail ganglia for five animals, from hatching to late larval development. These datasets allow us to separate the connectome into core connections, synapses that are present throughout the lifetime, transient connections, synapses that are present only during early or late development, and variable connections, synapses that are not conserved between animals. We propose that the core connections may drive hard-wired behaviors, and developmentally regulated connections exert stage-specific roles, while variable connections may confer individual variability and/or be stochastic in nature. Our current data analyses lead to two notions: First, developmentally regulated connections are enriched for synapses between sensory neurons, and with neuromodulatory neurons, while connections between interneurons are remarkably stable. This implies that for C. elegans, core circuits for decision-making are already established at birth, but their modulation and multi-sensory integration are refined or shaped during development. Second, variable connections, comprising about half of the connection edges in the published adult dataset, are prominent. Stochastic or experience dependent variability in connections may contribute to variability of behaviors set by hard-wired core connections.

Witvliet, D. et al. (2019) International Worm Meeting "Structural plasticity of the C. elegans connectome across development and between individuals."

Neubauer, M., Witvliet, D., Mitchell, J.K., Maeng, S., Meirovitch, Y., Chisholm, A.D., Wang, M.D., Shavit, N., Wang, Z., Ho, C.Y., Samuel, A.D.T., Lichtman, J.W., Koh, W.X., Schalek, R.L., Rehaluk, C., Mulcahy, B., Holmyard, D., Berger, D.R., Zhen, M., Cook, S.J.

[International Worm Meeting, 2019]

Nervous system development is widely thought to be optimized for precise wiring and efficient networks. Maintaining plasticity, however, is necessary for animals to adapt, learn, and evolve. This is especially evident during postembryonic development when newly born neurons are integrated into functioning neurocircuits. Rules for circuit plasticity and variability during and after development are poorly because circuit-level analyses across multiple animals and developmental time points are missing. Using electron microscopy, we mapped the connectome of the central nervous system for eight isogenic C. elegans animals spanning from birth to adulthood. These datasets reveal a highly dynamic circuit architecture, with a five-fold increase in synapse number across postembryonic development. Synapses are built and removed for multiple reasons: (1) to strengthen a remarkably stable core circuitry for decision-making, (2) to fine-tune multi-sensory integration and motor responses by building new unique cell-cell connections, (3) to streamline circuit computations, and (4) to fill connectivity gaps as a result of evolutionary pressures to hatch before initial wiring is complete. This remodeling is driven independently of the contact area between neurons and instead is dependent on neuron class and centrality. Remodeling is overrepresented between connections from sensory neurons to motor and interneurons, while connections between interneurons are remarkably stable. Well-connected, central neurons (typically interneurons), are more heavily regulated than other neurons, but surprisingly this regulation does not originate from other central neurons. Thus, the driving force for synaptic growth is not uniform, and may depend on neuron identity, suggesting an underpinning by genetic or functional identity. Together, our findings show that even in one of the most deterministic animals, nervous system wiring retains a high degree of plasticity. The connectome should be separated into core connections, that are present throughout life, developmentally changing connections, that depend on the stage of development, and variable connections, that are not conserved among individuals. Core connections are the strongest class of connections, but they make up less than half of all connections. The prevalence of wiring plasticity implicates relevance to nervous system adaptation and variability. Our data will be available on nemanode.org before the end of the summer.

Centonze VE et al. (1997) International C. elegans Meeting "FREE CALCIUM LEVELS FOLLOWING FERTILIZATION IN MUTANTS OF C. ELEGANS."

Strome S, Centonze VE, White JG, Polinko E

[International C. elegans Meeting, 1997]

A hallmark of fertilization is a transient increase in the level of free calcium in the newly fertilized oocyte. This calcium "spike" has been demonstrated during in vitro fertilization in a number of organisms. We are interested in whether C. elegans oocytes also exhibit a similar calcium spike at fertilization. Since the oocyte can not be removed from the ovary and remain viable we have circumvented this problem by imaging fertilization and early development in utero. Calcium indicator dyes [Ca-green dextran (10K) and Ca-crimson dextran (10K), Molecular Probes, Inc., Eugene, OR] were injected directly into oocytes. The worms with injected oocytes were subsequently anesthetized in 0.1% tricaine and 0.01% tetramisole to immobilize them for the purpose imaging. The all-solid-state multi-photon imaging system developed at the IMR was used to image the oocytes and embryos in timelapse. Both the fluorescence signal and the transmitted IR brightfield image were collected simultaneously. We detected fluctuations in the levels of cytoplasmic calcium during fertilization, second meiotic division and mitosis. We could not determine exactly when the sperm actually fertilizes the oocyte however, we observed both morphological as well as physiological changes that appear to be closely associated with the fertilization event. We detected pin point flashes of fluorescence in the cytoplasm which appear to occur just prior to the fertilization event. These flashes may indicate changes in the oocyte capacitance for fertilization. Later there was a rise in cytoplasmic calcium that appeared to be global. It is thought that this rise is a direct result of fertilization and corresponds to the calcium "wave" seen in other organisms. Immediately after this rise in calcium, the oocyte changes from a cylindrical to an oval shape and within a few seconds passes into the spermatheca. The elevations detected during meiosis and mitosis appear to be localized to specific regions or structures in the embryo such as the pronuclei and the mitotic centrosomes. Supported by NSF IBN-9117559 (S.S.) and NIH Biomedical Research Technology Grant RR 00570 (IMR, J.W.)

Jean-Michel Bellanger et al. (2003) International Worm Meeting "ZYG-9, TAC-1 and ZYG-8 cooperate to control microtubule behavior in the one-cell stage C. elegans embryo"

Jean-Michel Bellanger, Pierre Gonczy

[International Worm Meeting, 2003]

Proper spatial and temporal control of microtubule dynamics by microtubule associated proteins (MAPs) is essential for successful cell division. XMAP215 is an evolutionarily conserved MAP that plays a crucial role in stabilizing microtubules throughout the cell cycle. In C. elegans, the XMAP215-family member is encoded by zyg-9, which is required in one-cell stage embryos for a number of microtubule-dependent processes, including pronuclear migration (Matthews, L.R., et al., J Cell Biol, 1998. 141(5): p. 1159-68). zyg-8 encodes another evolutionarily conserved MAP required for proper cell division in C. elegans (Gonczy, P., et al., Dev Cell, 2001. 1(3): p. 363-75). ZYG-8 harbors a kinase domain and a Doublecortin domain that mediates microtubule stabilization. The function of zyg-8 is required in a temporally more restricted manner than that of zyg-9 since zyg-8 mutant embryos undergo normal pronuclear migration, but exhibit defective spindle positioning during anaphase. How ZYG-8 activity is regulated throughout the cell cycle and whether it may control microtubule dynamics by interacting with other MAPs remain to be elucidated. To begin addressing these questions, we sought molecular partners of ZYG-8 through a yeast two-hybrid screen. We identified the unique C. elegans member of the Transforming and Acidic Coiled-Coil (TACCs) family of proteins. In Drosophila, D-TACC localizes to spindle poles and controls microtubule behavior (Raff, J.W., Trends Cell Biol, 2002. 12(5): p. 222-5). Moreover, D-TACC physically interacts with the XMAP215 orthologue MiniSpindles, perhaps helping to recruit it to astral and spindle microtubules, thus ensuring their stabilization. In C. elegans, we found that pronuclear migration does not take place in tac-1 (RNAi) one-cell stage embryos, just like in zyg-9 mutant embryos. Consistent with the Drosophila data, we established that TAC-1 and ZYG-9 physically interact, both in vitro and in vivo. Furthermore, antibody staining and GFP-fusion protein expression studies revealed that TAC-1 mainly localizes to spindle poles during mitosis. Intriguingly, we found that the relationships between TAC-1 and ZYG-9 may rely on a mechanism that differs in part from that described in Drosophila. Indeed, we observed that tac-1 is required for ZYG-9 protein stability, and reciprocally. We are currently investigating the molecular basis of this effect, as well as the biological significance of the interaction between ZYG-8 and TAC-1.

Scholz, Monika et al. (2019) International Worm Meeting "Predicting locomotion from whole-brain neural dynamics in freely moving animals."

Randi, Francesco, Leifer, Andrew, Yu, Xinwei, Shaevitz, Joshua, Linder, Ashley, Scholz, Monika, Sharma, Anuj

[International Worm Meeting, 2019]

How do patterns of neural activity across the brain represent an animal's behavior? Recent techniques for recording from large populations of neurons are providing new insights into how locomotion is encoded in population-level neural activity. Studies from mammalian systems suggest that behavioral information may be more prevalent throughout the brain and may account for a larger fraction of neural dynamics than previously thought. In C. elegans, pioneering studies revealed that the worm's neural dynamics during immobilization exhibit striking stereotyped low-dimensional patterns of neural activity that dominate brain-wide dynamics (Kato et al., 2015). These dynamics are hypothesized to map onto a motor sequence consisting of forward, backward and turning locomotion. One interpretation is that the majority of the worm brain's activity may be involved in encoding these locomotory behaviors. Here we seek to directly measure how patterns of neural activity represent locomotion by recording brain-wide calcium activity in freely-moving animals. We record calcium activity simultaneously from the majority of head neurons in C. elegans during unrestrained spontaneous locomotory behavior (Scholz et al., 2018). We find that a subset of neurons distributed throughout the head encode locomotion. By taking a linear combination of these neurons' activity, we predict the animal's velocity and body curvature and further infer the animal's posture from neural activity alone. The collective activity of these neurons outperforms single neurons at predicting velocity or body curvature. We further attempt to estimate the identity of neurons involved in the prediction. Among neurons important for the prediction are well-known locomotory neurons, as well as neurons not traditionally associated with locomotion. We compare the neural activity of the same animal during unrestrained movement and during immobilization and observe large differences in their neural dynamics. Intriguingly, during unrestrained movement we estimate that only a small fraction of the brain's overall neural dynamics are encoding velocity and body curvature. We speculate that the rest of the brain's neural dynamics may be involved in encoding other behaviors, processing sensory information or maintaining internal brain states. Kato, S., Kaplan, H.S., Schrodel, T., Skora, S., Lindsay, T.H., Yemini, E., Lockery, S., and Zimmer, M. (2015). Global brain dynamics embed the motor command sequence of Caenorhabditis elegans. Cell 163, 656-669. Scholz, M., Linder, A.N., Randi, F., Sharma, A.K., Yu, X., Shaevitz, J.W., and Leifer, A. (2018). Predicting natural behavior from whole-brain neural dynamics. BioRxiv 445643.