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Monday, July 16, 2012

Watching a fly embryo develop in real time

We know a great deal about Drosophila melanogaster (aka fruit fly) development. After all, D. melanogaster is one of the most common model organisms in all of biological science. However, despite the thousands of studies involving this little insect, no one has been able to track the developmental path of every cell in its body. This is because cells migrate from top to bottom or front to back at specific stages of embryogenesis. If your camera is focused on the top, some of those cells will disappear out of view as they move through the larva’s body.

The solution is to have multiple cameras filming all sides simultaneously. This seemingly simple answer is a lot more complicated than it first appears. First, the organism must be illuminated so that you can see the individual cells without frying the creature. A technique known as ‘light sheet microscopy’, in which light is shined sideways onto the subject, has proven useful for observing single cells. Second, and perhaps most importantly, matching the different views seamlessly requires massive computing power that simply wasn’t available until recently.

Using a brand new microscope system they called SimView (simultaneous multi-view), Raju Tomer and his colleagues from Howard Hughes Medical Institute were able to simultaneously capture images of a fly larva from four different views. It took about 11 terabytes to merge them into the film you see below. As a reminder, this is a single fly embryo filmed from above and below at the same time. Each dot of light is a cell nucleus.

A similar study was led by Lars Hufnagel of the European Molecular Biology Laboratory. These researchers used their own new microscope, dubbed MuVi-SPIM for multi-view selective-plane illumination microscopy, to produce the following 3D film of a fruit fly embryo.

Needless to say, being able to track the developmental progress of each cell in a fly embryo is not just of interest to entomologists. D. melanogaster is a model for studying processes that occur in other organisms, including humans. Therefore, the more we understand about them, the more we understand about us.