Eyes without a face.

November 13, 2011 8:16 PM

Exposing our skin to the sun's ultraviolet rays unfortunately can give rise to a multitude of adverse health effects. Our skin's ability to produce melanin serves as buffer by absorbing those nasty UV rays. But how exactly does our skin know when it's being exposed to UV light? Well, apparently it can see it.

Rhodopsin, a pigment believed to be only found in the eye ( and necessary for the development of photoreceptor cells ) has been discovered in skin cells as the kickstarter for melanin production.

posted by Isosceles (21 comments total)

A real case of "The Skin Eye Live In".
posted by hanoixan at 8:50 PM on November 13, 2011 [2 favorites]

Genetics is object oriented.
posted by clarknova at 9:19 PM on November 13, 2011 [2 favorites]

Nah, genetics is a huge morass of unstructured copy-paste code and terrifyingly fragile hacks. It only works because we unit-test almost the whole thing before propagating any changes.
posted by hattifattener at 9:26 PM on November 13, 2011 [40 favorites]

So is there going to be a mechanism to flash yourself with a burst of UVA a few hours before going out in the day to optimize melanin?
posted by BrotherCaine at 9:33 PM on November 13, 2011

hattifattener: "Nah, genetics is a huge morass of unstructured copy-paste code and terrifyingly fragile hacks."

Not only that, it's all stuffed in main(), is full of #ifdef, case, and if…then…else statements (as well as moore than a few gotos), and keeps accessing variables outside of scope.

From the article, it looks like a case where they're using retinal as an identifier…
posted by Pinback at 9:46 PM on November 13, 2011 [2 favorites]

So is there going to be a mechanism to flash yourself with a burst of UVA a few hours before going out in the day to optimize melanin?

From the third link: After an hour, measurable amounts of melanin accumulate, although in relatively small quantities compared to the production that will occur within 24 hours.

Surely unless you're spending consecutive days in a cave, you'd be producing melanin on an ongoing basis as a result of exposure from the previous day so an artificial of UVA would be redundant?
posted by arcticseal at 9:59 PM on November 13, 2011

Know you're going to the beach tomorrow? Flash yourself with a burst of UVA today!
posted by davejay at 10:01 PM on November 13, 2011

So is there going to be a mechanism to flash yourself with a burst of UVA a few hours before going out in the day to optimize melanin?

They're called tanning beds and they are a very bad idea. You have heard of melanoma, right?
posted by longsleeves at 10:05 PM on November 13, 2011 [1 favorite]

Post title is full of win.
posted by Wolof at 10:11 PM on November 13, 2011 [3 favorites]

So, what are you are saying is my skin has seen me naked and masturbating?
posted by Samizdata at 11:02 PM on November 13, 2011 [1 favorite]

Fascinating. I wonder if you could target these cells with some drug to produce a tan, without needing to spend a lot of time in the sun. They have fake tanners now, but generally you end up with a pretty odd color, supposedly.
posted by delmoi at 11:33 PM on November 13, 2011

Can't access the actual paper right now, but why wasn't the rhodopsin detected in genome-wide expression gene quantitation screens 7 years ago? Melanoctyles make up 5-10% of skin cells if I recall correctly, so I suppose the expression might have been lost in the noise of regular fibroblasts (since the samples used were usually "skin" rather than a more useful FACS-sorted population).
posted by benzenedream at 11:41 PM on November 13, 2011

This post rocks in so many ways:

Scientific discovery..

Obscure 80s reference..

Nerdom code metaphors..

Thank you.
posted by tbonicus at 12:48 AM on November 14, 2011

I'm currently working towards a thesis for a project based in rod cells so this is kinda blowing me away.

If there is rhodopsin in skin cells (or within a specific subset of skin cells) then those cells (or cells close by) have to be able to produce retinal (the crazy kooky chromophore that sits within the protein opsin to make the full, complete, light sensing rhodopsin) which is usually made by Retinal Pigment Epithelial cells (RPE cells) that sit on the top end of the rod/cone cells and OM NOM NOM the 'used' top end of the rod cell Outer Segment (the unique organelle of rods and cones which facilitates the transformation of light into a neuronal signal) and recycle retinal back to the rods (in a super cool, membrane shuffling way).

We really don't have a firm grasp on the many of the details of the eating, or the passing back, or even of the formation of outer segments but the RPE cells are super necessary for rod cell survival (and if I remember correctly, development in utero).

Oh, and I know that was a little fast and furious there with the retinal biology, so if you actually want a good time and not a quickie check out this. I'll look up the name of a really great book that we all read as an introduction to retina when I can find it tomorrow morning.

TL DR: There are two populations of cells in retina that facilitate rhodopsin signaling, HOW IS SKIN DOING THAT.

Small article beef: technically they found opsin RNA and the proteins opsin and rhodopsin. Or at least I hope they found natually occurring rhodopsin without having to add in more retinal. Also, also, signal is triggered within a few seconds as opposed to retina's millisecond timing... interesting...
posted by Slackermagee at 12:59 AM on November 14, 2011 [8 favorites]

Don't skin cells have the DNA for every signaling protein and receptor? In the eye you need specialization because vision is amazing when you get right down to it. In the skin, well, if it can figure out the lights are kind of bright, good enough.
posted by Kid Charlemagne at 1:34 AM on November 14, 2011 [1 favorite]

Eyes without a Facebook.
posted by Wolof at 4:26 AM on November 14, 2011

It makes sense because the cutaneous melanocytes and light detecting cells of the retina have a common embryological ancestor. In fact, if you examine very primitive animals, such as flukes, they have specialized collections of cells on their heads which trigger a flight response when light shines on them. These cells, in a common ancestor, eventually became the eye.
posted by Renoroc at 5:00 AM on November 14, 2011 [2 favorites]

This article is very interesting. My husband has been telling me for several years that he read somewhere that tanning starts when your eyes detect the UV, so you're more likely to get a sunburn if you wear sunglasses. I've never been able to find any scientific evidence for this, but I'll admit I haven't looked super hard.

Don't skin cells have the DNA for every signaling protein and receptor?

Yes, all your cells have all the DNA for everything your body does. It's just that they can't or don't use it, because they have "differentiated" in a way that makes them specialists. As you noted, retina cells do need specialization because they do a really specific thing (sensing light), but they are not really any more specialized than, say, white blood cells, neurons, epithelial cells in your intestines, or any other cells. Even skin cells are specialized to do their job of protecting the body. Each kind of cell has a specific job that it is specialized to do.

That said, the stem cells you hear so much about in the news are like the grandfathers of all these specialized cells, and retain the ability to use most or even all of the DNA. Therefore they can produce daughter cells that can specialize into any of a wide range of functions. That's what makes them so exciting for medical research, because they could be used to help fix a variety of different kinds of damaged tissue.
posted by vytae at 9:04 AM on November 14, 2011

Don't skin cells have the DNA for every signaling protein and receptor?

The study looked at RNA, not DNA. RNA is typically used to copy data from DNA to make proteins, so if you have messenger RNA for something, it means that gene is being expressed.
posted by delmoi at 11:39 AM on November 14, 2011

Huh, that would provide an actual mechanism for some of the stuff I've seen about the advantages of sleeping in a totally dark room. Neat.
posted by restless_nomad at 1:39 PM on November 14, 2011

These findings may prompt reexamination of previous claims for human extraocular photoreception, including resetting circadian rhythms by illuminating the backs of the knees (Extraocular Circadian Phototransduction in Humans; No evidence for extraocular light induced phase shifting of human melatonin, cortisol and thyrotropin rhythms) and distinguishing colored light with fingertips (Dermal vision; Nonvisual color perception: A critical review).

Note that visible-wavelength photoreceptors in skin at different depths could provide color discrimination using the surrounding tissue as a filter, in the same way the Foveon image sensor uses silicon.
posted by 0rison at 4:15 PM on November 15, 2011