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Kara Cerveny, Steve Wilson's Lab, UCL
This photomicrograph shows the retina from the eye of a three-day-old zebrafish (Danio rerio). Zebrafish are small tropical freshwater fish that are widely used in scientific research. The retina is viewed here from the front, as if the viewer is looking directly into the eye of the fish. This image is of the whole eye, created by reflecting half the image across its origin to represent the naturally occurring perfect symmetry observed in the zebrafish.
What does this image show?
This image was created using double in situ hybridisation, a staining technique that identifies spatial expression of gene products. Using this method, structures can be identified by staining for genes known to be expressed in specific tissues.
Here, undifferentiated retinal stem cells have been highlighted in red. These cells will differentiate to become retinal neurons, which send visual signals to the brain. The cells that have already started to differentiate are highlighted in purple and are located at the periphery of the retina. The central yellow region is the lens. The captivating kaleidoscope effect is created by the elongated cells and the radiating growth of the undifferentiated region closest to the lens towards the differentiated cells on the periphery.
Why are zebrafish used in research?
The zebrafish is widely used as a model organism for research into vertebrate development. All vertebrates (animals with backbones) share an evolutionary origin, so zebrafish can offer insightful comparisons into human development.
Kara Cerveny explains: "To gain insight into the development of the retina we study the developing eyes of zebrafish. Zebrafish eyes, like the rest of their bodies, grow continuously and in a very controlled pattern." This allows them to investigate the signals that ensure the correct proliferation of these stem cells in the eye.
Zebrafish are a useful model for all aspects of development. They have a brief gestation and transparent eggs that develop outside of the female's body, which allows scientists to easily observe and manipulate their development. Their genome has been fully sequenced, with much of the sequencing work done at the Wellcome Trust Sanger Institute, Cambridge. More about the history of the zebrafish in scientific study is summarised in this Wellcome Trust feature.