Yuval Elani retweetledi
I'm fascinated by efforts to make animals (or parts thereof) photosynthetic.
For the latest attempt, published last week, researchers took thylakoids from plant chloroplasts (the little membranes that carry photosystem I and II proteins) and inserted them into the eyes of mice. Specifically, they gave the animals eye drops containing the thylakoids twice a day for five days.
The thylakoids went into corneal cells (apparently they are small enough that the cells endocytose them?) and did photosynthesis, making NADPH and ATP from light. This isn't a gene therapy, though; the eye cells cannot make more of these plant enzymes, and so the photosynthesis only happens for about 8 hours before the enzymes are destroyed.
Why do this in the eye? One reason is that light doesn't penetrate tissue deeply; maybe a millimeter. Therefore, the eye is one of the few parts of the body that actually gets light exposure. It is also -- maybe equally important -- immune privileged, meaning these plant proteins don't trigger an inflammatory reaction (which would likely happen in other tissues).
I'm not sure this paper has any real utility, at least not clinically. The authors say that it does (to help treat corneal injuries, for example) but I think it's just expected for authors to make up claims like this to get published in CNS journals.
The more interesting reason to read this paper, I think, is just that it shows light can be used as a direct "metabolic input" in mammalian cells. You can use light to make energy molecules and NADPH, which can then be used by the cell's normal pathways.
This isn't the first paper to do stuff like this, either. There is a rich history of (temporary) photosynthetic animals! In 2011, Christina Agapakis & co. injected living cyanobacteria into zebrafish embryos, and it worked. (No developmental impact on the fish.) In 2024, a Japanese team put chloroplasts from red algae into Chinese hamster ovary (CHO) cells, and the chloroplasts apparently survived and did photosynthesis for two days.
Biotechnologists have a great ability to harness GENES taken from nature to build useful tools and therapies. We can sequence the natural world, collect genes in databases, and use tools like AlphaFold to figure out what they code for.
But our ability to harness entire organelles -- structures crafted over millions of years of evolution, which perform functions that cannot be matched by genes alone -- is severely limited. Animal photosynthesis, and pursuits thereof, might be a useful way to start closing this gap.
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