New X-ray method shows how frog embryos could help thwart disease

An international team of scientists using a new X-ray method recorded the internal structure and cell movement inside a living frog embryo in greater detail than ever before.

This result showcases a new method to advance biological research and the search for new treatments for genetic diseases.

Scientists at Northwestern University and the Karlsruher Institut für Technologie in Germany, in collaboration with the Advanced Photon Source at the U.S. Department of Energy's Argonne National Laboratory, released the most precise depiction ever of the embryonic development of African clawed frogs, one of the most frequently studied model organisms in biology.

The results titled "X-ray phase-contrast in vivo microtomography probes new aspects of Xenopus gastrulation" were published May 16 in the journal Nature.

The team X-rayed an embryo during gastrulation, the period when its hundreds of cells start to organize into differentiated tissues that eventually form the nervous system, muscles and internal organs. Studies of African clawed frog embryos can provide clues to the evolution of vertebrates and how human genes turn on or off to create diseases.

Until now, however, it has been difficult to study these embryos. Classical absorption imaging requires a contrast agent and large X-ray dose that can harm living organisms. Researchers from the German synchrotron ANKA proposed a new method of nondestructive analysis using X-ray diffraction. The work was done at the APS outside Chicago because the APS's high-energy X-rays were required to prevent blurring of the image and damage to the sensitive embryos.

"To obtain the best possible results, a highly coherent high-energy X-ray source with high flux is necessary," said Xianghui Xiao, a scientist at the APS who collaborated on the work. "The APS is one of only a few X-ray lightsources in the world with this capability. The upgrade of the APS will further improve our ability to study the real-time movement of molecules in living organisms."

In the experiment, Xiao and his colleagues took regular 15-second exposures separated by periods of 10 minutes over the course of two hours of different gastrulas. The resulting 13 time-lapse scans provided a detailed portrait of the transfiguration of the frog cells.

"The motivation of the experiment was to be able to look at the process of how different larger structures develop at the cellular level in real time," Xiao said. "What we're doing is actually a kind of four-dimensional imaging."

The scientists discovered new morphological structures and clarified the process for redistributing fluid in the embryo. They also were able to locate the areas of the embryo that were driving the migration of tissues and cells during gastrulation

"X-ray diffraction enables high-resolution imaging of soft tissues," said Ralf Hofmann, one author of the study and a physicist at the Karlsruhe Institute of Technology in Germany. "In our work, we did not only mange to resolve individual cells and parts of their structure, but we could also analyze single cell migration, as well as the movement of cellular networks."