My research interest is centered around the functional dissection of sensory-to-motor transformation, combining developmental and evolutionary perspectives. Below is a brief description of my current/past projects.
Evolution of olfactory circuits in drosophilids
Neuroscientists, including myself, strive to learn the general principles on how the brain works, often using model organisms. However, use of a single model organism hinders the understanding of the rationale behind the circuit design (“Why is it designed that way?”) and the evolvability of circuit functions (“What twists can make the animal behave in a different but meaningful way?”). I believe that comparative, cross-species approaches to elucidate how nervous systems adapt to confer animals with unique behaviors will be an effective complementary way to extract general principles of brain organization and function.
In this project, I study the central olfactory circuts in Drosophila sechellia, a fly species endemic to the Seychelles archipelago. Drosophila sechellia is specialized to Morinda citrifolia, or noni fruit, which emits a pungent odor that is attractive for this species but not for its cousin species Drosophila melanogaster. Taking advantage of the shifted behavioral output despite the similarity of their nervous sytems, I compare the central olfactory circuits to elucidate how neuronal circuits evolve to enable behavioral adaptation and to understand the general principle of sensory processing.
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 836783.
This work was also supported by EMBO Long-Term Fellowships (ALTF 454-2019).
Wiring and miswiring of sensorimotor circuits in Drosophila larvae
Adaptive behavior of an animal is underpinned by the complex yet precise connectivity of its nervous system. The connectivity of a neuron within the network is established through precise neurite guidance and synapse formation mechanisms, which give rise to the unique shape of individual neurons. How does this “shape” code behavior?
In this project, I study the molecular mechanisms underlying the segment-specific axon guidance of Wave neurons (see below) and the effect of their manipulation on behavioral regulation. We found that manipulation of one gene in Wave neurons suffices to rewire the tactile circuit and induce different behavior in response to tactile inputs.
For details, see the following preprint:
Takagi S, Takano S, Morise S, Zeng X, Nose A. Segment-Specific Axon Guidance by Wnt/Fz Signaling Diversifies Motor Commands in Drosophila Larvae. Available at SSRN: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3990386
Segment-specific sensorimotor processing in Drosophila larvae
Sensory inputs of the same modality often elicit distinct behaviors depending on the location thereof. For instance, many animal species perform backward movement in response to head touch but perform forward movement to tail touch. How is the location-specificity realized in the brain? We showed that, in fruit fly Drosophila larvae, a class of segmentally-repeated interneurons (named Wave neurons) match their tactile receptive fields to appropriate motor programs by participating in different circuits in different segments.
For details, see the following publication:
Takagi S, Cocanougher BT, Niki S, Miyamoto D, Kohsaka H, Kazama H, Fetter RD, Truman JW, Zlatic M, Cardona A, Nose A. Divergent Connectivity of Homologous Command-like Neurons Mediates Segment-Specific Touch Responses in Drosophila. Neuron. 2017 Dec 20;96(6):1373-1387.e6. doi: 10.1016/j.neuron.2017.10.030. Epub 2017 Nov 30. PMID: 29198754.