Fine features of fruit fly captured in 3-D

Michael A. Greenwood

Scientists seeking to crack the mysteries of Alzheimer’s and other diseases that attack the human brain continue to look at the fruit fly for possible clues. The Drosophila melanogaster fruit fly and humans share many genes with similar functions, and the insect is frequently used in research to study how genes influence disease.

This 3-D image of a fruit fly was generated using optical projection tomography after first bleaching the fly’s exoskeleton. Various organs can be clearly seen. Images reprinted from PLoS One with permission of the researchers.

The problem is capturing the internal anatomy of the fruit fly on film. Its dark exoskeleton makes it impossible to image through the cuticle. Researchers are forced to dissect the flies and use either stereomicroscopy or compound or confocal microscopy. These techniques have a number of shortcomings, including the loss of tissue integrity and the inability to focus on a deep point within the tissue.

Researchers from the Medical Research Council Human Genetics Unit in Edinburgh, UK, and from Centre de Regulació Genòmica in Barcelona, Spain, may have found an alternative.

The optical projection tomography technique allowed researchers to image gene expression from inside the fly and to relate it to the rest of its anatomy.

They report that a dual technique involving bleaching away the color of an adult fruit fly combined with optical projection tomography allowed them to capture images of the fly’s internal and intact anatomy in 2-D optical cross sections and to capture 3-D images of organs in their natural surroundings that provided detailed information on shape and structure.

Using optical projection tomography, researchers identified neurodegenerative vacuoles in the brains of flies lacking the RNA editing enzyme Adar (adenosine deaminase acting on RNA). The vacuoles were confirmed by hematoxylin and eosin staining. With such images, scientists will no longer have to dissect the flies by hand to observe how genetic changes influence the loss of brain cells.

It also enabled them to visualize the size and shape of neurodegenerative vacuoles in the brains of flies suffering from age-related neurodegeneration. Additionally, they visualized taulacZ expression in 2- and 3-D. A full summary of the research can be found in the Sept. 5 issue of the online journal PLoS One.

The bleaching method of clearing also is suitable for confocal microscopy. Researchers imaged a fruit fly’s brain from the front (top row) and from behind (bottom row).

The bleaching technique also appears suitable for confocal microscopy. During experiments, the researchers avoided the usual step of dissection and captured detailed images a fruit fly’s brain.