Cell Luo Liqun's research team uses in vivo imaging to systematically reveal the developmental mechanism of the olfactory neural circuit in Drosophila

Editor | The brain is the most complex organ.
The human brain has ~1011 neurons.
Even the simple lower organism fruit fly has ~105 neurons
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In the process of brain development, each neuron needs to form a specific network connection structure through axons, dendrites and other neurons.
This accurate neuron connection controls various functions in adulthood
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An important issue for brain development is that when such a large number of neurons are searching for the neurons that need to be connected in the brain at the same time, how do they accurately locate the destination, especially the axons or dendrites of neurons.
Growing to a destination very far away from their cell size is equivalent to a planned "international travel"
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Previous studies on this issue have mostly focused on finding important genes that control neural connections, but this does not allow us to intuitively see how this "travel" occurs
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In order to solve this problem, on September 21, 2021, Chinese scientist Professor Luo Liqun from Stanford and his laboratory postdoctoral fellow Dr.
Tongchao Li (Tongchao Li is the first author of the paper and co-corresponding author with Professor Liqun Luo) will be published in Cell on September 21, 2021 Authored an article entitled Cellular Bases of Olfactory Circuit Assembly Revealed by Systematic Time-lapse Imaging
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As a classic research system, the olfactory neural circuit of Drosophila is relatively simple but has sufficient complexity.
At the same time, it is relatively easy to find neural connection errors.
It has been used to discover important genes that control the development of the circuit before.
Direct imaging of the living brain is troubled by the brain covering tissues
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This work uses the development of the olfactory neural circuit of Drosophila into a research system, and develops an in vitro culture system based on the antennae-brain of Drosophila.
By dissecting the developing Drosophila brain and the antennae where the olfactory sensory nerves are located at the same time The growth conditions in the body are simulated in the in vitro petri dish, and it is a good reproduction of how different olfactory nerves find the correct destination (olfactory bulb) and form connections with specific types of superior nerves during the development of the body, which makes them very capable.
Observe clearly how individual axons/dendrites find their final destination step by step
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Using a newly developed genetic tool, they were able to label a small number of single neurons from ~3000, 43 types of olfactory nerves (present in the antennae) in each brain, and through 24-hour continuous two-photon microscopy in vivo imaging, They observed how axons from 30 types of olfactory sensory nerves (90 single neurons) grow from antennae to specific areas of the brain.
For the first time, they systematically compared the specificity of so many types of axons in a small brain area at the same time.
Sexual growth behavior
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Their findings indicate that different types of olfactory sensory nerves have adopted different strategies in the process of looking for the target area, in the growth rate, the selection and determination of the target area, and the dynamic growth process to the target area.
Variety of behavior
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In order to record this dynamic process more clearly and quickly, they further discussed with Professor Eric Betzig (Nobel Prize winner in 2014) from Janelia Research Campus and his postdoctoral fellow Fu Tianming The Ph.
D.
collaborated to use a MOSAIC microscope with adaptive optics correction (an optical correction technology derived from astronomical telescopes) to update the growth of a single olfactory sensory nerve axon in the brain.
High-speed (30 seconds/3D scan) and clearer in vivo imaging.
It is worth mentioning that they discovered for the first time a new subcellular structure exploring branch located at the end of axon, which was used to approach the end of axon.
Detect the target signal at the time of the target
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In order to explain the various morphological changes of the axon terminal during the deliberately targeted growth process, they further observed the structure of the axon terminal granulocyte skeleton (cell filaments and microtubules).
Interestingly, they found that the nerves are in the brain When growing in a medium, it exhibits a completely different or even opposite cytoskeleton from when a single nerve grows in a petri dish (the classic model in previous textbooks).
Neural development is crucial
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In addition, Dr.
Tongchao Li and Professor Liqun Luo cleverly used microsurgical operations to remove unilateral olfactory sensory nerves during development.
This made them discover an interesting phenomenon: During development, the bilateral olfactory sensory nerves need each other.
To grow the olfactory bulb to the right target, especially the growth in the contralateral hemisphere, is regulated by the olfactory nerve from the contralateral reverse growth.
This experiment was difficult to achieve with traditional genetic manipulation methods before, and it also revealed that the left and right hemispheres The brain plays an important synergy during development
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In short, this article has developed a living tissue culture technology that can be used for high-resolution imaging of brain circuit development.
For the first time, it systematically observes the specific target-oriented growth behavior of 30 kinds of olfactory sensory nerve axons, using the most advanced Microscopy technology has further increased the limit of in vivo imaging and provided valuable information for our understanding of the development of brain circuits
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Original link: https://doi.
org/10.
1016/j.
cell.
2021.
08.
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Reprinting is prohibited without permission.
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