10/8/06

Le gene de la couleur de peau/ the skin color gene ?


(carte du monde selon la couleur de peau/world map according to skin color)
(Note: Le post en 2 langues, c'est pour tatie qui se met a l'anglais intensivement :) )

Francais:
LC24A5, voila le nom du gene qui serait le facteur determinant de la couleur de peau. Le Journal "Science", bible virtuelle des chercheurs , a publié l'étude d'un groupe de biologistes sur la pigmentation du "poisson zèbre"(?) sur ce gene responsable de la regulation de l'acidité des melanocytes. Ils ont découvert que ce gene a subi une mutation chez 99% de la population europeene et intact chez les populations ouest-africaines et asiatiques (etudes statistiques conduites a Berlin, Yaruba et Pekin si mes souvenirs sont bons). Ce gene n'explique pas toute l'histoire car sinon: 1) il n'existerait que 2 couleurs possibles: noir ou blanc 2) les chinois seraient beaucoup plus foncés qu'ils ne sont réellement. Néanmoins, 2 leçons à retenir selon lui: 1) la seule différence trouvée dans les mélanocytes des groupes: 2 degrés de pH du cytoplasme; sinon tout les autres "ingredients" sont identiques ( nombre de melanocytes, production de melanine...) 2) la couleur de peau par "défaut" est la couleur noir. Le leader de l'étude, venu à Purdue jeudi, explique que de la même manière que la drépanocytose a survécu à une sélection biologique darwinienne en Afrique car elle protège du paludisme, la couleur de peau blanche a "survécu" en Europe car l'exposition au soleil y est moindre. Je tiens à préciser que ces conclusions sont celles de l'auteur et non les miennes. D'un point de vue pratique, ces études pourraient conduire a un traitement pour le vitiligo (décoloration de la peau) dont souffre Michael Jackson (mais il a d'autres problèmes plus important, si je ne m'abuse...).
English:
SLC24A5: that is the gene that is supposed to be the determining factor in skin color. The journal "Science", virtual bible for researchers, published the study of a group of biologists on the pigmentation of "zebrafish"in which this gene was responsible for the regulation of ion exchange in melanocytes. They discovered that this gene is mutated into a truncated form in 99% of the white European population and intact in the West-African and Chinese populations. This gene does not explain the whole history because otherwise 1) there would be only 2 possible skin colors: black or white 2) the East-Asians would appear darker than they are. Nevertheless, 2 lessons were to be retained (according to him) : 1) the only difference found in the melanocytes of the different populations: 2 degrees of pH in the cytoplasm; all the others "ingredients" are identical (number of melanocytes, production of melanin...) 2) the skin color by "default" is black. The leader of the study, presenting at Purdue last thursday, explained that in the same manner sickle cell anemia "survived" the biological selection in Africa because it protects from malaria, the white skin color "survived" in Europe because the exposure to the sun is lesser over there. I make a point of pointing out that these conclusions are those of the author and not mine. From a practical point of view, these studies could lead to a cure for the vitiligo (discolouration of the skin) from which suffers Michael Jackson (but he may have other more important problems, if I am not mistaken...).



19 comments:

  1. that dude does have some major problems... didn't know about this talk, i always thought that melanocyte distribution was more concentrated in white people and less concentrated in black people. anyway brown is what, then, heterozygous ?

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  2. damn and there goes my arguement that everyone is a different shade of brown...

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  3. hey Mosi,
    yup, some major flaws in the study but I thought that transfecting a human gene in Zebrafish was pretty daring :). I think what he is saying is that this gene gives the blueprint of our skin color. He mentions that other factors would be the organization of the ER and Golgi in the melanocytes and their structures. He lost me after that :) but basically that is how he explains the shades of brown :)

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  4. really? so it's not different amounts of expressed melanin in different melanocytes?

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  5. nope, crazy isn't it ?

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  6. So how does one explain the "tanning" factor. For those of us who are already 'brown' can become 'browner' in sunlight.

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  7. hello there Video :),

    A chinese student asked a similar question during the talk: " I am rather pale but it takes 5 min in the sunlight for me to tan extensively, how is that related to this gene ?" The answer was somewhat dissapointing. The speaker went back to the organization of the melanocytes and showed that although the gene was intact in both populations, the histological organization of the melanocytes were different. He then reitarated than this gene was not the only factor in skin color but it is the main factor in deciding the "background" color (if you will). I thought it was interesting but also very unsatisfactory.
    cheers,

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  8. I like the fact that the default skin color is black :)

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  9. Hey there,

    Solely based on the fact that the wild type gene product results in black skin phenotype...:) but it sure doesn't hurt. :)

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  10. we're all african ! yay !

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  11. "Ich bin ein Schwarzwald(er)" :)

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  12. Hey,
    Angie as Mariane Pearl. Great? Bad? No opinion?
    Facts are, the book was not about origins and skin colour and (even if I didn't read it) the actress who plays the lead role must be as touching and powerful as the woman she portrays. Maybe a Halle Berry is storming around somewhere (héhé love this one) or a perfect tanned Thandie Newton is ...( what is she doing ?...) Both are talented but I don't think they could make enough mediatic buzz for the movie!
    Brangelina are doing a great job making polemics (Team Jolie anyone?) and they found the best way to bring attention to things that really matter (telllll me about it). Jolie might not be a great actress but sure... she knows how to be a better human. (yes this one was beautiful...)!
    So can a half-quebecoise-iroquoise-irish make a credible half-french-cuban-chinese-african ?
    oh well...it doesn't really matter!!!
    bizzz

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  13. hello Jo,
    Personally, Angie could play E.T. and I would still buy it. :) and you are right, I cannot think of anyone else who could be more fitting for this role, not because of her acting ability or looks but because of what she represents to the world ( a citizen-of-the-world- straight-talking-no-BS-courageous woman)
    wonder how it feels to be 30ish and have Angie portraying you (M.Pearl), must be a bit surreal....

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  14. Ce me rappelle la démonstration du prof de bio que la notion de race n'a absolument rien de scientifique mais uniquement une connotation culturelle.J'ai adoré!

    Cela fait longtemps que je ne m'étais pas plongée dans l'analyse de ce genre de conclusion mais disons qu'elles ne sont pas très solides.
    Ok pour la relation entre la drépanocytose et la barrière contre le palu. D'ailleurs, la majorité des Malgaches seraient homozygotes pour le gène de la drépa, autrement, ce serait l'hécatombe.
    Je ne pense pas qu'un seul gène soit à l'origine de la couleur de peau, la binarité de la conclusion démontre la faille. Peut-être un gène dans le contrôle de la mélanogenèse ou dans le rôle physiologique de la mélanine..

    Si mes souvenirs sont bons, effectivement, l'étude habituelle de comparaison des gènes, au plus proche du génome humain, se fait avec celui du tetraodon (poisson-ballon)et plus récemment avec celui du poisson-zèbre.On devra beaucoup aux poissons, moi j'dis!

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  15. Tattum, ton amour de l'ocean te perdra :). Ca m'a etonne qu'un journal comme Science mette cette etude sur leurs couvertures. C'est clair que d'autres facteurs doivent entrer en jeu. Ils ont quand meme preciser que couleur de peau etait loin d'etre =race.

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  16. Hey, Ranjit passed on your regards! Thanks! Apparently you were in la scala at the same time! I must've walked right past cos I din't see you. Anyway, I passed!

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  17. Congrats, video ! That's awesome. We got a head start to dinner at La scala. The funny thing is that we thought of going to bistro 501 to join you guys..:-)
    after the prelim, it's cruise control from here on :) sort of

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  18. 1) Il faut bien être malgache pour s'intéresser autant à la couleur de la peau :P (faux les études ont été faites par des non-malgaches :P)

    2) Ça n'explique pas (comme tu le soulignes) qu'il y ait différentes couleurs de peau entre les individus d'un même peuple, d'une même région ou voire d'une même famille...

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  19. Salut Lilia,
    :) Un malgache serait capable de discerner les differences de teintes entre marron noix de cajou et marron caramel ;)....helas :(. Mais je crois qu'on est pas les seuls: plusieurs temoignages des Philippines, Inde et Cote d'Ivoire accordent une importance trop grande aux nuances de couleur. Je suis juste inquiet que cette etude sera utilisee a des fins douteuses....

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