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Researchers explores how a cell’s fate is determined or what happens in the womb to turn a developing cell into a specific type of cell, an aspect of human biology that is largely unknown. Thefteam ocused on the cells that allow people to see blue, red and green-the three cone photoreceptors in the human eye.
Trichromatic color vision delineates human from other mammals, as the cells grew in the lab and became full-blown retinas, the team found the blue-detecting cells materialized first, followed by the red- and green-detecting ones. In both cases, they found the key to the molecular switch was the ebb and flow of thyroid hormone.
The level of the hormone wasn’t controlled by the thyroid gland, which of course isn’t in the dish, but entirely by the eye itself. Understanding how the amount of thyroid hormone dictated whether the cells became blue or red and green, the team was able create retinas that if they were part of a complete human eye, would only see blue, and ones that could only see green and red.
The finding that thyroid hormone is essential for creating red-green cones provides insight into why pre-term babies, who have lowered thyroid hormone levels as they are lacking the maternal supply, have a higher incidence of vision disorders.