The new age of bioimaging — Page 7 of 7  < Back

Brain bending

A narrow tube of cells forms in a zebrafish embryo just hours after conception. As the cells divide, the walls of the tube bend and fold, creating cavities that fill with fluid. Postdoc Jennifer Gutzman uses a spinning-disc laser microscope to take pictures of these elaborate structures, which eventually mature into brain cavities. She makes movies of the developing brain, capturing the movement of individual cells.

Jennifer Gutzman

“The movies shed light on our own minds, as the early stages of development are virtually identical among fish and humans,” says Gutzman, who works in Whitehead Member Hazel Sive’s lab.

Scientists have already identified dozens of proteins that control neural patterning by mutating genes and watching for brain defects. Gutzman decided to characterize some of these defects in detail at the cellular level. She began by tracking individual cells in normal (mutation-free) embryos to establish a reference point.

Preparing the specimens took a huge chunk of time. She injected a fertilized egg with a piece of RNA encoding a green fluorescent protein that binds to cell membranes and outlines every individual cell. She let the zebrafish develop overnight, and in the morning, just before each embryo turned 18 hours old, she placed jelly-like material on a slide and used a pipette to pluck out a piece, wedging the young critter in the resulting hole. She added water and a covering before racing to a spinning-disc laser microscope equipped with a heater (to keep the specimen warm) to conduct her experiment during the correct phase of development.

Next came the imaging. She programmed the microscope to take virtual slices of the developing embryo every five minutes, creating a three-dimensional movie. In the past, scientists used scanning laser confocals to accomplish this task, but they often damaged specimens because they took so long to generate pictures.

“To create a single stack of 200 images, scanning laser confocals bathe specimens in light for about 15 minutes,” says Gutzman. “A spinning-disc laser confocal can accomplish the same task in just 20 seconds.”

The new technology allowed her to keep specimens alive long enough to create the perfect four-hour movie. Next, she will make movies of mutant embryos and compare them to the originals.

“It is extraordinary to be able to look at the developing brain as it forms and see what cells are doing,” says Sive. “This is an enormous leap in understanding mechanisms underlying brain development.”

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