By Sean Henahan, Access Excellence

Graphic: a photo of a  glowing fly head

The researchers engineered a gene including a fluorescence protein from  the jellyfish Aequorea victoria into fly eggs. The new gene is a hybrid between a fly gene that contributes to cell structure during development and the green fluorescent protein (GFP) gene. GFP emits bright green light when exposed to ultraviolet or blue light.

The researchers used GFP to tag the protein, which attaches to the cell's actin cytoskeleton, a meshwork that helps cells keep their shape and migrate from one place to another during the transformation from fertilized egg to adult fly. All the flies that made the fluorescent protein appeared remarkably normal, researchers said.

"Previous cell staining methods required toxic fixatives, which means each image is only a snapshot of what is happening in the cell. We wanted to follow movement in a dynamic way, and this fluorescent protein allowed us to do that. It's like going from photographs to a full-length motion picture," explained Daniel Kiehart, associate professor of cell biology, Duke University.

Research in the field of developmental biology has shown that fruit flies contain much of the same basic genetic programming that determines the growth and development of  humans from a fertilized egg into a healthy baby. But because mammals gestate their young inside the body, it is very difficult to follow key developmental steps. Studying fruit flies, also known as Drosophila melanogaster, has become the research method of choice.

Kiehart and his colleagues want to know why cells move during development. They plan to identify which genes are crucial for normal movements and cell shape changes during development, and why, when gene products don't function at the right time, birth defects can result.

One key protein is non-muscle myosin, a kind of molecular motor that drives changes in cell shape and powers cell movements as a fertilized fly egg grows and develops legs, eyes, wings and all its other body parts. Scientists also know that myosin is vital to daily cell maintenance in both flies and people. Kiehart has already identified one type of non-muscle myosin that, when missing in flies, results in a defect in the way cells change shape, comparable to spina bifida in people.

By watching the fate of the glowing cells in his experimental flies, Kiehart and his colleagues have already confirmed some of their previous hypotheses about cell movement during dorsal closure. They also have provided a powerful tool for other researchers studying development, because the glowing protein is also concentrated in the developing eye, nervous system, the forming gut, the sensory organs, and particularly, the leading edges of migrating cells in all organ systems.

For example, the Duke researchers can now observe directly the actin-rich microvilli -- or little fingers -- form in the developing eye, particularly in the light receptor cells, retina and optic lobe. "This localization may make it easier to study formation of the eye, and to find genes involved in eye development," Kiehart said.

"We believe this new tool for studying cell shape change will provide a rich source of information that will open up one of the final frontiers of developmental biology: morphogenesis or cell growth and maturation," he said. "The ability to observe cell shape and structure should contribute to our understanding of human disease as well."

The research appears in the Nov. 1, 1997 issue of the  journal Developmental Biology.