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Behind the picture: How fly eye cells get their shape

The main goal of the Pichaud lab at the MRC Laboratory for Molecular Cell Biology at University College London is to understand how fly eye cells get their shape. But why do fly eyes matter? And how can studying fruit fly eyes help us fight cancer in humans? Franck Pichaud and Rhian Walther explain all.

Image: Fruit fly photoreceptors imaged with confocal microscope. Copyright : Franck Pichaud Lab

Image: Fruit fly photoreceptors imaged with confocal microscope. Copyright : Franck Pichaud Lab

On first glance these bright blobs looks a bit like the multi-coloured lights of tiny disco balls. But these incandescent shapes are the perfectly formed outlines of cells which let light in to the fruit fly eye – photoreceptor cells.

In summer, you may find a few of these extra ‘guests’ buzzing around your kitchen.  The lowly fruit fly, or Drosophila melanogaster, is quite partial to pungent food and drink including ripe bananas and wine – cheap or fine, they aren’t fussy.

Much like epithelial cells in humans, you can see that the fruit fly photoreceptor cells in the picture have defined shapes. And because of their parallels with human cells, these tiny critters have helped scientists answer some of the big questions in biology.

The fruit fly was the organism of choice for Thomas Hunt Morgan, who was awarded a Nobel Prize in 1933 for his pioneering work in genetics.  Since then, thanks to its genetic toolbox (75% of disease genes in humans have corresponding genes in fruit flies), the fruit fly has been buzzing around the Nobel committee, getting recognition for work on DNA damage, embryonic pattern formation, smell, immunity, and circadian rhythms.

We use the fruit fly eye to study epithelial cells, which make up the lining of most human organs, including our lungs, skin and colon. Cancers that develop in epithelial cells (also known as carcinomas) have devastating consequences because the cells are so widespread.  And a characteristic feature of carcinomas is misshapen epithelial cells. So understanding how these cells keep their shape can help scientists identify the cause of these cancers and also provides clues for potential diagnosis and treatment options.

To find out how photoreceptor cells get into shape, we use cutting-edge confocal microscopy technologies. We look at different parts of the cell by labeling proteins found at the cell surface with fluorescent ‘tags’.  In the picture you can see that the pink (attached to F-actin proteins) and yellow (attached to Crumbs proteins) blobs form a regular pattern and are always found in the same place.

When the pattern is upset, we know that the cell shape has been disrupted. Misshapen cells no longer work properly, which is the case in carcinomas. Our goal, therefore, is to take advantage of the fruit fly’s genetic toolbox to understand which genes are responsible for keeping epithelial cells in shape.

Provided that they have a steady hand (a fruit fly is about the size of a sesame seed), and with the help of powerful microscopes, scientists can use fruit fly eyes as a ‘mini model’ that mimics epithelial cells in humans, in ways that are not possible in other experimental systems such as mice.

For this reason, the fruit fly photoreceptor cell will remain a reliable workhorse – or perhaps ‘work-fly’ is more appropriateto promote our understanding of how epithelial cells keep in shape throughout our lives.

Search #LMCBimageoftheweek on Twitter to see more fascinating images from the @MRC_LMCB.


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