Synthetic Biology – Project Proposal
Augmenting human vision with hybrid opsin pigment production via gene therapy
(a collaboration with Don Miller and Corey van Sice)
As a proposed synthetic biology application we explored the viability of using viral vectors to insert new opsin pigment genes into human cone cells in the retina. We proposed the adaptation of opsin genes from the common pigeon (Columba livia f. domestica) as well as the zebrafish (Cyprinidae Cypriniformes). The pigeon having 5 distinct cone cell types (a pentachromat) has the ability to perceive light into the infrared range of the spectrum. The zebrafish with 4 distinct cone cell types (a tetrachromat) can perceive light within the ultraviolet range of the spectrum. The goal would be to enable the perception of both infrared and ultraviolet light in humans; expanding our trichromacy to functional pentachromacy.
Current Success with Monkeys
In 2009 Jay Neitz successfully inserted human L-opsin genes into the retina of two colorblind squirrel monkeys (Saimiri sciureus) using viral vector gene therapy at the University of Washington. After 20 weeks the monkeys’ were able to perceive red and green. The two male monkeys were born colorblind carrying only one X chromosome, they carry only one version of opsin pigment gene and are therefore red-green color blind. A similar condition exists in humans with dichromatic colorblindness. Fewer female squirrel monkeys have the condition because they carry two X chromosomes. The major breakthrough besides the effective use of gene therapy to cure colorblindness is the reversal of the previously accepted notion that a developed visual cortex would not be able to multiplex the new sensory information into discernable variation in color tone.
“It doesn’t seem like new neural connections have to be formed, you can add an additional cone opsin pigment and the neural circuitry and visual pathways can deal with it.”—says András Komáromy, a vision researcher and veterinary ophthalmologist at the University of Pennsylvania in Philadelphia, who was not involved in the research.
Tetrachromacy in Humans
In humans, two cone cell pigment genes are located on the sex X chromosome, the classical type 2 opsin genes OPN1MW and OPN1MW2. It has been suggested that as women have two different X chromosomes in their cells, some of them could be carrying some variant cone cell pigments, thereby possibly being born as full tetrachromats and having four different simultaneously functioning kinds of cone cells, each type with a specific pattern of responsiveness to different wave lengths of light in the range of the visible spectrum. One study suggested that 2–3% of the world’s women might have the kind of fourth cone that lies between the standard red and green cones, giving, theoretically, a significant increase in color differentiation. Another study suggests that as many as 50% of women and 8% of men may have four photopigments. [wikipedia]
This suggests that tetrachromacy is at least physiologically viable in humans in some form making the the introduction of new opsin genes feasible. Using a viral vector to insert the additional opsin genes into human cone cells is a potential method:
While having the ability to see what others can not offers a range of advantages including military, safety inspection, emergency response.