Color vision research originated in mice and the study of cones and light processing, however, new research using zebrafish has allowed researchers from the University of Tokyo to understand the evolutionary benefits of developing color vision and the processes that may cause color blindness.
Zebrafish are consistently used in medical research for a few reasons:
- Their entire genome is sequenced meaning researchers can easily identify irregularities in their genetic makeup or create mutations to study genetic functions.
- Zebrafish share 70% of their genes with humans.
- They are transparent so researchers can see their internal structures evolve and develop.
- 84% of human disease genes have a zebrafish counterpart meaning researchers can compare the physiological response of zebrafish to a disease to that of a human.
In a study from the University of Tokyo, researchers were able to genetically modify zebrafish’s cones. Cones are the part of the eye that makes color vision possible. In combination with rods, cones intercept light’s wavelengths and allow us, and fish, to process and color. By combining the study of genome sequences that create the types of cones specific to certain light waves and the gene-editing tools that allow us to modify genes, researchers were able to turn off the cones within zebrafish’s eyes that see blue and green light.
How Do Genes Affect Eyesight?
With the exception of a fogged mask on the eye’s cornea and the presence of additional cones in some fish species, fish eyes are very similar in structure to human eyes. Both use rods and cones to process external stimuli. This stimulus is then relayed via the nervous system to the brain by a chain reaction of electrical charges. Fish can also see a variety of color combinations, similar to humans. In fact, some fish species can see even more hues and colors than humans can! These similarities in genetic and structural makeup are the reason researchers have begun to use fish to study vision rather than mice.
Mice cannot distinguish between blue and green colors. Their vision is limited to wavelengths that do not contain those colors. This is simply how mice evolved differently than humans and fish. In humans and fish, however, color is important to survival (for fish) and understanding of their community and culture (for humans).
Researchers identified three types of genes that are present in creatures with four cones that can process four different light wavelengths. These cones are controlled by the following genes: six6b, six7, and foxq2. Foxq2 controls the processing of blue light and activates the six6b and six7 genes to send the blue lights’ signals to the brain.
In their study, researchers were able to turn off the foxq2 gene in the zebrafish’s genome sequences. This blocked blue light from the zebrafish’s cones and forced their eyes to adapt to shorter processing sequences that ultimately did not process the color blue. This process and blockage helped researchers determine two things:
- They were able to discover the importance of the color blue to zebrafishes’ survival. Zebrafish who could not process blue light had a harder time finding food in their environment.
- They were able to study the process of activating and deactivating a gene that affects color processing.
The Impact of Understanding Zebrafish’s Color Processing
By activating and deactivating the foxq2 gene in zebrafish, researchers made a breakthrough in understanding humans’ color blindness. By studying the interaction of genes in a genome sequence as they process different wavelengths, researchers can eventually apply this research to correcting color blindness in human patients.
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- Wikimedia, Available here: https://upload.wikimedia.org/wikipedia/commons/6/6b/Zebrafish_%2826436913602%29.jpg
- Science Daily, Available here: https://www.sciencedaily.com/releases/2021/10/211007122152.htm
- University of Tokyo, Available here: https://www.u-tokyo.ac.jp/focus/en/press/z0508_00192.html
- In-Fisherman, Available here: https://www.in-fisherman.com/editorial/understanding-fish-vision/154655
- Your Genome, Available here: https://www.yourgenome.org/facts/why-use-the-zebrafish-in-research