Drosophila connectome

The Drosophila connectome, once completed, will be a complete list of the roughly 135,000 neurons in the brain of the fruit fly Drosophila melanogaster, along with all of the connections (synapses) between these neurons. As of 2020, the Drosophila connectome is a work in progress, being obtained by the methods of neural circuit reconstruction. A stack of EM images of an entire brain exist, suitable for sparse tracing of specific circuits. A full connectome of a large portion of the central brain is likewise available. Many of the 76 compartments of the Drosophila brain have connectomes available, and the remainders are subjects of ongoing study.

Why Drosophila

Connectome research (connectomics) has a number of competing objectives. On the one hand, investigators prefer an organism small enough that the connectome can be obtained in a reasonable amount of time. This argues for a small creature. On the other hand, one of the main uses of a connectome is to relate structure and behavior, so an animal with a large behavioral repertoire is desirable. It's also very helpful to use an animal with a large existing community of experimentalists, and many available genetic tools. Drosophila looks very good on these counts:

  • The brain contains about 135,000 neurons,[1] small enough to be reconstructed in the near future.[2]
  • The fruit fly exhibits many complex behaviors. Hundreds of different behaviors (feeding, grooming, flying, mating, learning, and so on) have been qualitatively and quantitatively studied over the years.
  • The genetics of the fruit fly are well understood, and many (tens of thousands) of genetic variants are available.
  • There are many electrophysiological, calcium imaging, and other studies ongoing with Drosophila.

Current status

A high-level connectome, at the level of brain compartments and interconnecting tracts of neurons, exists for the full fly brain.[3] A version of this is available online.[4]

Detailed circuit-level connectomes exist for the lamina[5][6] and a medulla[7] column, both in the visual system of the fruit fly, and the alpha lobe of the mushroom body.[8]

In May of 2017 a paper published in bioRxiv presented an electron microscopy image stack of the whole adult female brain at synaptic resolution. The volume is available for sparse tracing of selected circuits.[9][10]

In 2020, a dense connectome of half the central brain of Drosophila was released,[11] along with a web site that allows queries and exploration of this data.[12] The methods used in reconstruction and initial analysis of the connectome followed.[13]

A natural question is whether the connectome will allow simulation of the fly's behavior. However, the connectome alone is not sufficient. Additional information needed includes gap junction varieties and locations, identities of neurotransmitters, receptor types and locations, neuromodulators and hormones (with sources and receptors), the role of glial cells, time evolution rules for synapses, and more.[14]

See also

References
  1. Alivisatos, A. Paul; Chun, Miyoung; Church, George M.; Greenspan, Ralph J.; Roukes, Michael L.; Yuste, Rafael (2012). "The brain activity map project and the challenge of functional connectomics". Neuron. 74 (6): 970–974. doi:10.1016/j.neuron.2012.06.006. PMC 3597383. PMID 22726828.
  2. Deweerdt, Sarah (2019). "How to map the brain". Nature. 571 (7766): S6–S8. Bibcode:2019Natur.571S...6D. doi:10.1038/d41586-019-02208-0. PMID 31341309.
  3. Chiang, Ann-Shyn; et al. (2011). "Three-Dimensional Reconstruction of Brain-wide Wiring Networks in Drosophila at Single-Cell Resolution". Current Biology. 21 (1): 1–11. doi:10.1016/j.cub.2010.11.056. PMID 21129968.
  4. "FlyCircuit - A Database of Drosophila Brain Neurons". Retrieved 30 Aug 2013.
  5. Meinertzhagen, I. A.; O'Neil, S. D. (1991). "Synaptic organization of columnar elements in the lamina of the wild type in Drosophila melanogaster". Journal of Comparative Neurology. 305 (2): 232–263. doi:10.1002/cne.903050206. PMID 1902848.
  6. Rivera-Alba, Marta; et al. (2011). "Wiring Economy and Volume Exclusion Determine Neuronal Placement in the Drosophila Brain". Current Biology. 21 (23): 2000–2005. doi:10.1016/j.cub.2011.10.022. PMC 3244492. PMID 22119527.
  7. Takemura, Shin-ya; et al. (8 August 2013). "A visual motion detection circuit suggested by Drosophila connectomics". Nature. 500 (7461): 175–181. Bibcode:2013Natur.500..175T. doi:10.1038/nature12450. PMC 3799980. PMID 23925240.
  8. Takemura, S. Y.; et al. (2017). "A connectome of a learning and memory center in the adult Drosophila brain". eLife. 6: e26975. doi:10.7554/eLife.26975. PMC 5550281. PMID 28718765.
  9. Yeager, Ashley (31 May 2017). "Entire Fruit Fly Brain Imaged with Electron Microscopy". The Scientist Magazine. Retrieved 2018-07-15.
  10. Zheng, Zhihao; et al. (2017-05-22). "A Complete Electron Microscopy Volume of the Brain of Adult Drosophila melanogaster". bioRxiv 10.1101/140905.
  11. Shan Xu, C.; et al. (2020). "A connectome of the adult Drosophila central brain". bioRxiv 10.1101/2020.01.21.911859.
  12. "Analysis tools for connectomics". HHMI.
  13. Scheffer, Louis K.; et al. (2020). "A Connectome and Analysis of the Adult Drosophila Central Brain". bioRxiv 10.1101/2020.04.07.030213.
  14. "Columbia Workshop on Brain Circuits, Memory and Computation, 2019".

Further reading
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