How, the people want to know, does a fruit fly's brain form?
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Or maybe you don't want to know that, but ground-breaking software tells us anyway. The scientists are also working on a more advanced life form, the zebrafish, and suggest that insights into the primitive animals' nervous-system development could shed light on our own.
The secret to the unprecedented advance in brain-development imaging lay in developing software that could handle the terabytes of data being produced by researchers at the Janelia Research campus at the Howard Hughes Medical Institute, Virginia, in almost real time, rather than weeks on end.
The researchers wanted to track, precisely, how a given cell turns into a given organ, for instance the brain. "What are the fundamental principles that rule the mechanisms of development? How do you actually get from one cell to a complex multicellular organism in a very robust manner?" asks Phillip Keller leader of the research at Janelia.
Until now, nobody actually knew that. Then a couple of years ago Keller and his group developed the simultaneous multi-view "light sheet microscope" which captures three-dimensional images of cells with unprecedented speed and precision over a period of days.
The tell-tale color system
Bioinformatics expert Fernando Amat explains that the team developed a color system allowing them to track individual cells during brain development. "We assign a color, a random color, to each cell at the beginning and then we propagate these colors based on the tracking information. So, what you can see is basically how each single-cell as they divide they go to different parts of the organism," Amat explained.
Thanks to the color map, the scientists can know what the original cell was that created each tissue in the embryo. And thus the scientists build a blueprint of how brains form in the fruit fly.
In the first attached video, each dot represents a single cell in forming brain of a fruit fly embryo. The second shows a zebrafish's brain thinking.
Yes, fetal fruit flies are very small, yet the program produces images in unprecedented detail. Formerly, organizing the mountains of data from the microscope into visualizations that the scientists could study took weeks. The new software can do it in a matter of minutes, mapping the process of cells forming into a complex nervous system.
Earlier this month the Janelia crowd reported using mutated zebrafish, whose neurons fluoresce under laser light when excited, to simply watch the nerve cells fire under the microscope. Put otherwise, they were watching the fish's brain live. That is the basics of the "light sheet" imaging technology.
Why were these two animals chosen, by the way? Regarding the fruit fly, Drosophila melanogaster, it's been a favorite of geneticists and biological scientists for decades, being incredibly easy to breed and very short-lived – you can see the effects of mucking about with their genes the next day. And as for zebrafish, Danio rerio, they also breed fast, are also hardy – and the babies are conveniently transparent.
Although it is true that the team is imaging brain development in fruit pests and small fish, which are relatively lowly, they have what to teach about the complex development of human nervous systems, Keller says. And meanwhile, admit that you always wanted to know the origin of the fruit fly's suboptical ganglia.