DNA in Cut Hair ?


by pkc111
Tags: hair
pkc111
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#1
Apr5-12, 01:00 AM
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Is it true that hair that is cut from your head (not pulled), does not contain any nuclear dna ?

My understanding of hair structure is that it is a matrix with at least some dead cells present in various layers. Eg the outside cuticle is made of flattened cells .
Feughelman, Max Mechanical properties and structure of alpha-keratin fibres: wool, human hair and related fibres, Sydney, UNSW Press (1996) ISBN 0868403598

Did these cells ever have a nucleus containing DNA, which broke down perhaps ?


Further,

What are the large dark spots shown in the following cross-section of a hair ?
http://en.wikipedia.org/wiki/File:Gray945.png

Thanks very much
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tal444
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#2
Apr6-12, 03:57 PM
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Hair that has been cut does not contain DNA. DNA is only found in live hair follicles, which means you need to uproot hair in order to obtain DNA. Hair is made up of keratin, which has the same structure in all human beings.
Pythagorean
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#3
Apr6-12, 06:31 PM
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theoretically, no. Technically, you probably have plenty of skill cells stuck in your hair.

pkc111
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#4
Apr7-12, 05:56 PM
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DNA in Cut Hair ?


Hair that has been cut does not contain DNA. DNA is only found in live hair follicles, which means you need to uproot hair in order to obtain DNA. Hair is made up of keratin, which has the same structure in all human beings.
I still dont undertstand how hair can have a cellular structure, each cell with an apparent nucleus, yet that nucleus not now contain DNA ?

I understand hair to be made up of dead cells (from image above and reference above), however I dont understand how DNA molecules can detriorate so quickly after leaving the follicle by growth, when surrounded by a stable matrix. My understanding is that nuclear DNA has been preserved in dead tissue for years and used in forensic cases.
Pythagorean
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Apr8-12, 03:06 AM
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I don't know the conditions of DNA preservation, but hair is a sink: it has massive surface area for it's volume, so it tends to dry quickly and adjust to ambient temperatures quickly. It would be hard to maintain concentration gradients in that environment without nutritional support and a lot of living parts of the cell would quickly degrade in most environments.

And this is after apoptosis; I have no idea about the details of that, especially in the specific context of hair.

Now, you can actually recover DNA form mitochondria in hair cells (mitochondria are organelles that have their own DNA) but that gives ambiguous results between a maternal family line (they wouldn't be able to tell you from your mother or any of her offspring).
pkc111
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Apr8-12, 06:06 PM
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I don't know the conditions of DNA preservation, but hair is a sink: it has massive surface area for it's volume, so it tends to dry quickly and adjust to ambient temperatures quickly. It would be hard to maintain concentration gradients in that environment without nutritional support and a lot of living parts of the cell would quickly degrade in most environments.
If relatively fast physical degradation of the hair DNA was from environmental causes as suggested, I would expect there to be a steep concentration gradient of DNA throughout the length of the shaft (very high at the base of the exposed shaft through to least concentration at the tip). Bearing in mind that the maximum age of the hair shaft tip on some people when they get a haircut is less than 1 month.

Obviously degradation of DNA in a cell by the environment is not instant, if it were then any forensic DNA investigation would be extremely hard.

Also, wouldnt you expect environmental degradation of DNA in the hair cell to be accompanied by a visible change to the shape of the nucleus, the micrographs dont seem to show this ?
Pythagorean
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Apr8-12, 11:03 PM
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But remember that there's some kind of apoptosis first; it's likely the dead cells are extruded after their contents have been recycled, leaving behind mostly just structural components. Given my ignorance of apoptosis in this situation, I can't really comment. But what you're seeing could just be structural proteins from the nucleus left behind. They may even make up the bulk of what can be visualized of the living nucleus; that doesn't mean there's anything functional going on inside.
Pythagorean
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Apr8-12, 11:16 PM
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Also, looking at your picture, are you sure the little black dots are nuclei? How do you know they're not a keratine structures left-over form apoptosis?
pkc111
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Apr9-12, 05:59 PM
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You didn't say which dark spots, since the inner spots are indentified, I'm assuming you mean the pigment spots in the cortex?
I was referring to the larger dark spots at the centre of most circular structures shown in the figure, ie in the positions cell nuclei would sit.
bobze
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Apr9-12, 07:48 PM
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Quote Quote by pkc111 View Post
I was referring to the larger dark spots at the centre of most circular structures shown in the figure, ie in the positions cell nuclei would sit.
The lithograph from Gray's Anatomy depicts a hair follicle, not a cross-section of grown out hair. The "dark spots" are nuclei in cells that reside in the follicle that function in support and progenitor roles.

Edit; You can tell because the structures the diagram depicts. The "hyaline membrane" here is the basement membrane. The cortex and medulla are the hair proper, which are composed of anucleate, dead, keratinized cells. The cells outside of this are still living cells and do have nuclei.

As a hair grows out the cells which compose it undergo keratinization, just like with your skin, where the nucleus and cellular contents are degraded and ejected--Leaving essentially squished squamous cell bags of keratin.

Like someone pointed out above then, in theory cut hair should have no DNA because any cellular components left behind are anucleate. However, I'm sure the process isn't perfect and some cells with DNA present probably get trapped in your hair (for instance if a hair was pulled out at the follicle and then subsequently became trapped in the rest of your hair)--You'd likely also be able to find non-host DNA in there as well from other organisms that often live in hair.

Some better pictures in H&E;




Link for more reading.

Edit again; It might help you to see it cut longitudinally instead of cross section. Match up the parts from your link to this picture to understand what you are looking at;



So the cross section you supplied would be a cut near the top of this longitudinal view.
Evo
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#11
Apr9-12, 08:22 PM
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Thank you Bob! I guess my example was wrong.


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