From Embryo to Larva: Microscope Observes Fly Growth

For the first time, a two-and-a-half- hour-old fruit fly embryo was filmed in 3-D using a new microscope that rapidly images biological processes in thick samples at unprecedented detail.

The video was obtained using the Multi-View SPIM (selective-plane illumination microscopy) microscope developed in Lars Hufnagel’s lab at the European Molecular Biology Laboratory. It allows the viewer to see how cells on the embryo’s belly dive in to form what is known as the ventral furrow. Other cells can be seen moving around the embryo’s rear end to its back, in a process called convergent extension. Later, when an opening appears in the embryo’s back, one can track the process known as dorsal closure, during which surrounding cells close the gap.

Shown is the setup of a new microscope that enables scientists to film a developing fruit fly embryo in 3-D for more than 20 hours. (Images: ©EMBL/U.Krizic)

“This video shows a fruit fly embryo from when it was about two-and-a-half hours old until it walked away from the microscope as a larva, 20 hours later,” Hufnagel said. “It shows all the hallmarks of fruit fly embryonic development in three dimensions.”

The scientists documented this growth using the Multi-View SPIM, or MuVi-SPIM, which builds on previously developed EMBL SPIM technology. As with SPIM, the new microscope shines a thin sheet of light on the embryo, illuminating one sample layer at a time to obtain an image of the whole sample with minimal light-induced damage. MuVi-SPIM, on the other hand, takes four full images from different angles, eliminating the need to rotate the sample. This speeds up the process and for the first time enables researchers to merge the four images into a single high-quality 3-D image.

Hufnagel’s team can obtain an image of a fruit fly embryo in a few seconds, and be ready to repeat the process. The different images that make up the video are taken in such rapid succession that very little in the embryo changes from one frame to the next. Because of this, scientists are sure of where each cell is, and even where structures inside of cells are, and track these throughout the video. Using such rapid imaging enabled the team to record the movements of every nucleus in the embryo not only during the later developmental stages, but also throughout the first three hours of its life, when nuclei divide very quickly.

A new microscope, MuVi-SPIM, allows scientists to image rapid biological processes in thick samples at unprecedented detail.

“Everything in this microscope is optimized for speed and light sensitivity,” said Uros Krzic, a member of Hufnagel’s lab and designer of the microscope. “Not just the optics, mechanics and cameras, but also the software that controls the microscope and processes the data. We can finally get high-quality data in real time.”

Next, the scientists plan to use the microscope to investigate how organs and tissues form, not just in the fruit fly but in other model organisms as well.

The findings appeared June 3 in an advance online publication of Nature Methods.

For more information, visit: www.embl.de