Luminous fruit flies unlock the secrets of development
Scientists at Duke University Medical Center were able to use protein markers to directly follow the embryonic development of fruit flies. They hope to use this method to facilitate the observation of development processes. Most people might think of a spooky green glowing bow tie as a Halloween prank. However, scientists at Duke University Medical Center have added a fluorescent jellyfish protein as a marker to an important protein for the cell structure of fruit flies. They want to uncover how fruit flies develop from embryos to larvae and finally to adult flies. The scientists believe their research may also contribute to a better understanding of birth defects in humans.
In the recently published study, they examined dorsal closure during embryonic development in flies. This process is comparable to the closure of the neural tube in mammalian fetuses.
The scientists used a time-lapse camera and a high-resolution light microscope to capture a dorsal closure in flies on video for the first time. They believe this new information will help them understand what causes spina bifida. Spina bifida is a birth defect in which the spine does not close properly during development. There remains a hole in the spine that needs to be surgically closed after birth.
The findings of researchers led by Daniel Kiehart, professor of cell biology at Duke University Medical Center, were published in Developmental Biology Nov. 1. They describe how they made flies glow by inserting a lab-constructed gene into fly eggs. The new gene is a cross between a fly gene, which contributes to cell structure during development, and the green fluorescent protein (GFP) gene from the jellyfish Aequorea victoria. GFP emits bright green light when exposed to ultraviolet or blue light.
The research team used GFP to tag a protein that binds to actin in the cell's cytoskeleton. The cytoskeleton plays an important role in the development from the fertilized egg to the adult insect, since it is responsible, among other things, for changes in the location of the cells. All of the flies that produced the fluorescent protein appeared to develop remarkably normally, according to the researchers.
"Previous methods of staining cells required toxic fixatives, so each image represents just a snapshot of what is happening inside the cell," said Kiehart. “We wanted to follow the movement dynamically. This fluorescent protein allows us to do that. It's like going from photographs to a full-length movie.”
Drosophila contain some of the same basic genetic programming that drives the complicated journey from a fertilized human egg to a he althy baby. Therefore, in Kiehart's view, studying the fruit fly - also known as Drosophila melanogaster - can tell something about our own evolution. Kiehart and his colleagues are now focusing on how and why cells move during development. They want to find out which genes are responsible for normal movement and changes in cell shape during development and why birth defects can occur when the gene products don't work at the right time.
A key protein, according to Kiehart, is myosin, which is found outside of muscles. This myosin controls changes in cell shape and supports cell movement during growth and differentiation of flies. It is also vital for normal cellular functions in both flies and humans. Kiehart has already identified a type of this myosin. A lack of this type in flies leads to cell deformations comparable to those seen in spina bifida in humans.
With GFP, other researchers also have an effective research tool. This is because the glowing protein produced by the altered gene is also found in the developing eyes, nervous system, gut, sensory organs, and particularly in the "migratory" cells of all organ systems. For example, Duke University scientists can now directly observe how the actin-containing microvilli form in the developing eye, specifically in the receptor cells and retina. "This localization makes it easier to study the formation of the eye and to find genes involved in the development of the eye," said Kiehart.
Kiehart and his lab team are expanding the use of this glowing protein. You want to find out how skin cells move to cover an open wound. They succeeded in inserting the glowing protein into the skin cells of humans and mice in a Petri dish in the laboratory. According to Kiehart, human cells actively produce the glowing protein and it does not appear to be toxic to them.
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