TY - GEN AB - The development, evolution, and function of the vertebrate central nervous system (CNS) can be best studied using diverse model organisms. Amphibians, with their unique phylogenetic position at the transition between aquatic and terrestrial lifestyles, are valuable for understanding the origin and evolution of the tetrapod brain and spinal cord. Their metamorphic developmental transitions and unique regenerative abilities also facilitate the discovery of mechanisms for neural circuit remodeling and replacement. The genetic toolkit for amphibians, however, remains limited, with only a few species having sequenced genomes and a small number of transgenic lines available. In mammals, recombinant adeno-associated viral vectors (AAVs) have become a powerful alternative to genome modification for visualizing and perturbing the nervous system. AAVs are DNA viruses that enable neuronal transduction in both developing and adult animals with low toxicity and spatial, temporal, and cell-type specificity. However, AAVs have never been shown to transduce amphibian cells efficiently. To bridge this gap, we established a simple, scalable, and robust strategy to screen AAV serotypes in three distantly-related amphibian species: the frogs Xenopus laevis and Pelophylax bedriagae, and the salamander Pleurodeles waltl, in both developing larval tadpoles and post-metamorphic animals. For each species, we successfully identified at least two AAV serotypes capable of infecting the CNS; however, no pan-amphibian serotype was identified, indicating rapid evolution of AAV tropism. In addition, we developed an AAV-based strategy that targets isochronic cohorts of developing neurons – a critical tool for parsing neural circuit assembly. Finally, to enable visualization and manipulation of neural circuits, we identified AAV variants for retrograde tracing of neuronal projections in adult animals. Our findings expand the toolkit for amphibians to include AAVs, establish a generalizable workflow for AAV screening in non-canonical research organisms, generate testable hypotheses for the evolution of AAV tropism, and lay the foundation for modern cross-species comparisons of vertebrate CNS development, function, and evolution. AU - Jaeger, Eliza C.B. AU - Vijatovic, David AU - Deryckere, Astrid AU - Zorin, Nikol AU - Nguyen, Akemi L. AU - Ivanian, Georgiy AU - Woych, Jamie AU - Arnold, Rebecca C AU - Ortega Gurrola, Alonso AU - Shvartsman, Arik AU - Barbieri, Francesca AU - Toma, Florina-Alexandra AU - Gorbsky, Gary J. AU - Horb, Marko E. AU - Cline, Hollis T. AU - Shay, Timothy F. AU - Kelley, Darcy B. AU - Yamaguchi, Ayako AU - Shein-Idelson, Mark AU - Tosches, Maria Antonietta AU - Sweeney, Lora Beatrice Jaeger ID - 15016 T2 - bioRxiv TI - Adeno-associated viral tools to trace neural development and connectivity across amphibians ER - TY - JOUR AB - Vertebrate movement is orchestrated by spinal inter- and motor neurons that, together with sensory and cognitive input, produce dynamic motor behaviors. These behaviors vary from the simple undulatory swimming of fish and larval aquatic species to the highly coordinated running, reaching and grasping of mice, humans and other mammals. This variation raises the fundamental question of how spinal circuits have changed in register with motor behavior. In simple, undulatory fish, exemplified by the lamprey, two broad classes of interneurons shape motor neuron output: ipsilateral-projecting excitatory neurons, and commissural-projecting inhibitory neurons. An additional class of ipsilateral inhibitory neurons is required to generate escape swim behavior in larval zebrafish and tadpoles. In limbed vertebrates, a more complex spinal neuron composition is observed. In this review, we provide evidence that movement elaboration correlates with an increase and specialization of these three basic interneuron types into molecularly, anatomically, and functionally distinct subpopulations. We summarize recent work linking neuron types to movement-pattern generation across fish, amphibians, reptiles, birds and mammals. AU - Wilson, Alexia C AU - Sweeney, Lora Beatrice Jaeger ID - 13097 JF - Frontiers in Neural Circuits SN - 1662-5110 TI - Spinal cords: Symphonies of interneurons across species VL - 17 ER - TY - JOUR AB - Amyotrophic lateral sclerosis (ALS) leads to a loss of specific motor neuron populations in the spinal cord and cortex. Emerging evidence suggests that interneurons may also be affected, but a detailed characterization of interneuron loss and its potential impacts on motor neuron loss and disease progression is lacking. To examine this issue, the fate of V1 inhibitory neurons during ALS was assessed in the ventral spinal cord using the SODG93A mouse model. The V1 population makes up ∼30% of all ventral inhibitory neurons, ∼50% of direct inhibitory synaptic contacts onto motor neuron cell bodies, and is thought to play a key role in modulating motor output, in part through recurrent and reciprocal inhibitory circuits. We find that approximately half of V1 inhibitory neurons are lost in SODG93A mice at late disease stages, but that this loss is delayed relative to the loss of motor neurons and V2a excitatory neurons. We further identify V1 subpopulations based on transcription factor expression that are differentially susceptible to degeneration in SODG93A mice. At an early disease stage, we show that V1 synaptic contacts with motor neuron cell bodies increase, suggesting an upregulation of inhibition before V1 neurons are lost in substantial numbers. These data support a model in which progressive changes in V1 synaptic contacts early in disease, and in select V1 subpopulations at later stages, represent a compensatory upregulation and then deleterious breakdown of specific interneuron circuits within the spinal cord. AU - Salamatina, Alina AU - Yang, Jerry H AU - Brenner-Morton, Susan AU - Bikoff, Jay B AU - Fang, Linjing AU - Kintner, Christopher R AU - Jessell, Thomas M AU - Sweeney, Lora Beatrice Jaeger ID - 8914 JF - Neuroscience SN - 0306-4522 TI - Differential loss of spinal interneurons in a mouse model of ALS VL - 450 ER - TY - JOUR AB - Motor output varies along the rostro-caudal axis of the tetrapod spinal cord. At limb levels, ∼60 motor pools control the alternation of flexor and extensor muscles about each joint, whereas at thoracic levels as few as 10 motor pools supply muscle groups that support posture, inspiration, and expiration. Whether such differences in motor neuron identity and muscle number are associated with segmental distinctions in interneuron diversity has not been resolved. We show that select combinations of nineteen transcription factors that specify lumbar V1 inhibitory interneurons generate subpopulations enriched at limb and thoracic levels. Specification of limb and thoracic V1 interneurons involves the Hox gene Hoxc9 independently of motor neurons. Thus, early Hox patterning of the spinal cord determines the identity of V1 interneurons and motor neurons. These studies reveal a developmental program of V1 interneuron diversity, providing insight into the organization of inhibitory interneurons associated with differential motor output. AU - Sweeney, Lora Beatrice Jaeger AU - Bikoff, Jay B. AU - Gabitto, Mariano I. AU - Brenner-Morton, Susan AU - Baek, Myungin AU - Yang, Jerry H. AU - Tabak, Esteban G. AU - Dasen, Jeremy S. AU - Kintner, Christopher R. AU - Jessell, Thomas M. ID - 7698 IS - 2 JF - Neuron SN - 0896-6273 TI - Origin and segmental diversity of spinal inhibitory interneurons VL - 97 ER - TY - JOUR AU - Sweeney, Lora Beatrice Jaeger AU - Kelley, Darcy B ID - 7699 IS - 10 JF - Current Opinion in Neurobiology SN - 0959-4388 TI - Harnessing vocal patterns for social communication VL - 28 ER - TY - JOUR AB - Neural circuit assembly requires selection of specific cell fates, axonal trajectories, and synaptic targets. By analyzing the function of a secreted semaphorin, Sema-2b, in Drosophila olfactory receptor neuron (ORN) development, we identified multiple molecular and cellular mechanisms that link these events. Notch signaling limits Sema-2b expression to ventromedial ORN classes, within which Sema-2b cell-autonomously sensitizes ORN axons to external semaphorins. Central-brain-derived Sema-2a and Sema-2b attract Sema-2b-expressing axons to the ventromedial trajectory. In addition, Sema-2b/PlexB-mediated axon-axon interactions consolidate this trajectory choice and promote ventromedial axon-bundle formation. Selecting the correct developmental trajectory is ultimately essential for proper target choice. These findings demonstrate that Sema-2b couples ORN axon guidance to postsynaptic target neuron dendrite patterning well before the final target selection phase, and exemplify how a single guidance molecule can drive consecutive stages of neural circuit assembly with the help of sophisticated spatial and temporal regulation. AU - Joo, William J. AU - Sweeney, Lora Beatrice Jaeger AU - Liang, Liang AU - Luo, Liqun ID - 7785 IS - 4 JF - Neuron SN - 0896-6273 TI - Linking cell fate, trajectory choice, and target selection: Genetic analysis of sema-2b in olfactory axon targeting VL - 78 ER - TY - JOUR AB - During assembly of the Drosophila olfactory circuit, projection neuron (PN) dendrites prepattern the developing antennal lobe before the arrival of axons from their presynaptic partners, the adult olfactory receptor neurons (ORNs). We previously found that levels of transmembrane Semaphorin-1a, which acts as a receptor, instruct PN dendrite targeting along the dorsolateral-ventromedial axis. Here we show that two secreted semaphorins, Sema-2a and Sema-2b, provide spatial cues for PN dendrite targeting. Sema-2a and Sema-2b proteins are distributed in gradients opposing the Sema-1a protein gradient, and Sema-1a binds to Sema-2a-expressing cells. In Sema-2a and Sema-2b double mutants, PN dendrites that normally target dorsolaterally in the antennal lobe mistarget ventromedially, phenocopying cell-autonomous Sema-1a removal from these PNs. Cell ablation, cell-specific knockdown, and rescue experiments indicate that secreted semaphorins from degenerating larval ORN axons direct dendrite targeting. Thus, a degenerating brain structure instructs the wiring of a developing circuit through the repulsive action of secreted semaphorins. AU - Sweeney, Lora Beatrice Jaeger AU - Chou, Ya-Hui AU - Wu, Zhuhao AU - Joo, William AU - Komiyama, Takaki AU - Potter, Christopher J. AU - Kolodkin, Alex L. AU - Garcia, K. Christopher AU - Luo, Liqun ID - 7701 IS - 5 JF - Neuron SN - 0896-6273 TI - Secreted semaphorins from degenerating larval ORN axons direct adult projection neuron dendrite targeting VL - 72 ER - TY - JOUR AB - Longitudinal axon fascicles within the Drosophila embryonic CNS provide connections between body segments and are required for coordinated neural signaling along the anterior-posterior axis. We show here that establishment of select CNS longitudinal tracts and formation of precise mechanosensory afferent innervation to the same CNS region are coordinately regulated by the secreted semaphorins Sema-2a and Sema-2b. Both Sema-2a and Sema-2b utilize the same neuronal receptor, plexin B (PlexB), but serve distinct guidance functions. Localized Sema-2b attraction promotes the initial assembly of a subset of CNS longitudinal projections and subsequent targeting of chordotonal sensory afferent axons to these same longitudinal connectives, whereas broader Sema-2a repulsion serves to prevent aberrant innervation. In the absence of Sema-2b or PlexB, chordotonal afferent connectivity within the CNS is severely disrupted, resulting in specific larval behavioral deficits. These results reveal that distinct semaphorin-mediated guidance functions converge at PlexB and are critical for functional neural circuit assembly. AU - Wu, Zhuhao AU - Sweeney, Lora Beatrice Jaeger AU - Ayoob, Joseph C. AU - Chak, Kayam AU - Andreone, Benjamin J. AU - Ohyama, Tomoko AU - Kerr, Rex AU - Luo, Liqun AU - Zlatic, Marta AU - Kolodkin, Alex L. ID - 7702 IS - 2 JF - Neuron SN - 0896-6273 TI - A combinatorial semaphorin code instructs the initial steps of sensory circuit assembly in the Drosophila CNS VL - 70 ER - TY - JOUR AB - By combining gene expression profiling with image registration, Tomer et al. (2010) find that the mushroom body of the segmented worm Platynereis dumerilii shares many features with the mammalian cerebral cortex. The authors propose that the mushroom body and cortex evolved from the same structure in the common ancestor of vertebrates and invertebrates. AU - Sweeney, Lora Beatrice Jaeger AU - Luo, Liqun ID - 7703 IS - 5 JF - Cell SN - 0092-8674 TI - ‘Fore brain: A hint of the ancestral cortex VL - 142 ER - TY - JOUR AB - Axon-axon interactions have been implicated in neural circuit assembly, but the underlying mechanisms are poorly understood. Here, we show that in the Drosophila antennal lobe, early-arriving axons of olfactory receptor neurons (ORNs) from the antenna are required for the proper targeting of late-arriving ORN axons from the maxillary palp (MP). Semaphorin-1a is required for targeting of all MP but only half of the antennal ORN classes examined. Sema-1a acts nonautonomously to control ORN axon-axon interactions, in contrast to its cell-autonomous function in olfactory projection neurons. Phenotypic and genetic interaction analyses implicate PlexinA as the Sema-1a receptor in ORN targeting. Sema-1a on antennal ORN axons is required for correct targeting of MP axons within the antennal lobe, while interactions amongst MP axons facilitate their entry into the antennal lobe. We propose that Sema-1a/PlexinA-mediated repulsion provides a mechanism by which early-arriving ORN axons constrain the target choices of late-arriving axons. AU - Sweeney, Lora Beatrice Jaeger AU - Couto, Africa AU - Chou, Ya-Hui AU - Berdnik, Daniela AU - Dickson, Barry J. AU - Luo, Liqun AU - Komiyama, Takaki ID - 7705 IS - 2 JF - Neuron SN - 0896-6273 TI - Temporal target restriction of olfactory receptor neurons by semaphorin-1a/plexinA-mediated axon-axon interactions VL - 53 ER - TY - JOUR AB - Gradients of axon guidance molecules instruct the formation of continuous neural maps, such as the retinotopic map in the vertebrate visual system. Here we show that molecular gradients can also instruct the formation of a discrete neural map. In the fly olfactory system, axons of 50 classes of olfactory receptor neurons (ORNs) and dendrites of 50 classes of projection neurons (PNs) form one-to-one connections at discrete units called glomeruli. We provide expression, loss- and gain-of-function data to demonstrate that the levels of transmembrane Semaphorin-1a (Sema-1a), acting cell-autonomously as a receptor or part of a receptor complex, direct the dendritic targeting of PNs along the dorsolateral to ventromedial axis of the antennal lobe. Sema-1a also regulates PN axon targeting in higher olfactory centers. Thus, graded expression of Sema-1a contributes to connection specificity from ORNs to PNs and then to higher brain centers, ensuring proper representation of olfactory information in the brain. AU - Komiyama, Takaki AU - Sweeney, Lora Beatrice Jaeger AU - Schuldiner, Oren AU - Garcia, K. Christopher AU - Luo, Liqun ID - 7704 IS - 2 JF - Cell SN - 0092-8674 TI - Graded expression of semaphorin-1a cell-autonomously directs dendritic targeting of olfactory projection neurons VL - 128 ER - TY - JOUR AB - The Sir2 deacetylase modulates organismal life-span in various species. However, the molecular mechanisms by which Sir2 increases longevity are largely unknown. We show that in mammalian cells, the Sir2 homolog SIRT1 appears to control the cellular response to stress by regulating the FOXO family of Forkhead transcription factors, a family of proteins that function as sensors of the insulin signaling pathway and as regulators of organismal longevity. SIRT1 and the FOXO transcription factor FOXO3 formed a complex in cells in response to oxidative stress, and SIRT1 deacetylated FOXO3 in vitro and within cells. SIRT1 had a dual effect on FOXO3 function: SIRT1 increased FOXO3's ability to induce cell cycle arrest and resistance to oxidative stress but inhibited FOXO3's ability to induce cell death. Thus, one way in which members of the Sir2 family of proteins may increase organismal longevity is by tipping FOXO-dependent responses away from apoptosis and toward stress resistance. AU - Brunet, Anne AU - Sweeney, Lora Beatrice Jaeger AU - Sturgill, J Fitzhugh AU - Chua, Katrin AU - Greer, Paul AU - Lin, Yingxi AU - Tran, Hien AU - Ross, Sarah AU - Mostoslavsky, Raul AU - Cohen, Haim AU - Hu, Linda AU - Chen, Hwei-Ling AU - Jedrychowski, Mark AU - Gygi, Steven AU - Sinclair, David AU - Alt, Frederick AU - Greenberg, Michael ID - 7706 IS - 5666 JF - Science SN - 0036-8075 TI - Stress-dependent regulation of FOXO transcription factors by the SIRT1 deacetylase VL - 303 ER -