In order to understand how the cells that enable us to perceive color (so-called cones) are created, researchers from the John Hopkins University in Baltimore (USA) have created an organoid of the eye: in practice, they grew stem cells in the lab, differentiating them into retina cells (the tissue that transforms light waves into nerve impulses) and then activating “growth” similar, in many aspects, to what happens during foetal development. The results of the experiment were published in the journal Science.
Researchers realized, over several months, that the cells capable of perceiving the color blue are those that are formed first, followed by those that “gather” red and green. The role of thyroid hormones (called T3 and T4), which the researchers administered to the cells, appeared to be fundamental in this transformation process: these molecules – discovered the researchers – act as true and proper switches in the development of retina cells. The organoid was able to manage (modulate) the hormones provided by the researchers independently, and start the differentiation of the cells sensitive to the color blue, followed by the others. However, the researchers also tried to “force” the outcome, providing different concentrations of the thyroid hormones, prompting the formation of retina cells capable of “seeing” only blue, or only green or red.
The discovery that T3 and T4 hormones are essential for the creation of the cells photosensitive to color also helps to understand why premature babies that are born well before term are more susceptible to several vision disorders (major thyroid deficiencies, due to the interruption of the flow of hormones from the mother can hamper the development of retina cells). The studies of the team from Baltimore could be useful for developing new therapies: “If we manage to interact with what brings a cell to its final ‘form’”, explained Kiara Eldred, co-author of the study, “We are also closer to the possibility of recovering the color vision in people with damaged retinal photoreceptors”.
However, was it really necessary to use an organoid to carry out this research? Yes, replies Kiara Eldred, because the laboratory animals normally used for studies on the eye (mice and fish) do not have the ability to see color like the human eye does.