Laboratory-grown retinas explain why humans perceive colours but canines do not.
A faculty member from Johns Hopkins University has made a significant finding regarding how vitamin A stimulates the production of particular cells, enabling human beings to perceive millions of colours. This ability is not observed in canines, felines, or other non-primate animals.
The use of retinal organoids enabled the research group to investigate a human-specific characteristic in a novel manner, as explained by associate professor of biology and author Robert Johnston. He stated that the subject of what distinguishes us as human beings and sets us apart is enormous.
The results, published in PLOS Biology, enhance our comprehension of age-related vision loss, colour blindness, and additional conditions affecting photoreceptor cells. Additionally, they disclose how genes regulate the production of color-recognition cells in the human retina—a function previously attributed to thyroid hormone levels.
The research team discovered, through manipulation of the organoids’ properties, that retinol acid is the molecule responsible for determining whether a particular cone cell specialises in green or red light. A crimson sensor is exclusive to humans with normal vision and close primate relatives.
Decades were devoted to the scientific consensus that red cone cells formed randomly. Recent research, however, conducted by Johnston’s group, indicates that thyroid hormone levels may regulate the process. According to the new analyses, retinol acid in the eye regulates a particular sequence of events that results in the formation of red blood cells.
The only significant difference between green and red cone cells is the opsin protein, which distinguishes between the two and transmits information regarding the colours humans perceive to the brain. The transformation of a cell into a green or red sensor is determined by a distinct set of opsins, even though the genomes of each cell remain 96% identical. By employing an innovative methodology that discerns these imperceptible genetic variations in organoids, the research group monitored fluctuations in the cone cell ratio for two hundred days.
Additionally, the researchers mapped the fluctuating ratio of these cells in the retinas of 700 adults. Changing the proportion of green to red cone cells in humans is one of the most unexpected findings of the new study, according to scientific team member Sara Haddinak.
Without affecting human vision, the reason for the plethora of variations remains a mystery to scientists. Johnston argues that if these cell categories determined the length of the human arm, then anatomically distinct lengths would result from varying cell ratios.
Scientists are making an effort to comprehend conditions like macular degeneration. They aim to increase understanding of the connections between cone cells and other cells and the nervous system.
According to Johnston, in the future, the researchers intend to assist individuals with vision impairments. It will be some time before that occurs, but the fact that the team can produce these various varieties of cells is highly encouraging, he continues.
