Melanin research

[melaninman]

The Many Benefits of Melanin Print E-mail
Tuesday, 08 January 2008
It has also been shown that Caucasians have higher concentrations of a more deleterious form of melanin known as “Pheomelanin.” The type of melanin that causes blonde and red hair actually increases the risk for cell death. Melanin filters out UV radiation, but it also increases UV harmful effects and causes cell death, particularly when the melanin is the kind found in light hair or skin (Brash et al., 2004).The resulting sunlight sensitivity of individuals with any particular melanin type would reflect the balance between protection and damage, with pheomelanin contributing 3-fold greater damage than eumelanin and perhaps less efficient protection (ibid). In this scenario, when a pheomelanin-containing individual visits the beach, his melanosomes act as microscopic x-ray sources to generate superoxide and OH_ radicals. Pheomelanin also produces almost five times as much superoxide as eumelanin after UV exposure (Persad et al, 1983).
Blonde Hair & Blue Eyes, bad for you??

By Bernie Douglas (January 8, 2008)

Although it is well known that Caucasians suffer from higher rates of skin cancer than do those with more skin pigment -- for example, In the U.S., rates of basal and squamous cell carcinomas are 50 times higher in Caucasians than in African Americans and African Americans have a 13-fold lower incidence of melanoma than do Caucasians (Tadokoro et al, 2003) – many are unaware of skin pigment’s (melanin) other beneficial properties. For example, calcium regulation in melanocytes (cells that produce pigment) affects numerous biological pathways including protecting the redox (oxidation and reduction) balance in the cell (William, 2007). Melanin has also been implicated in maintaining calcium homeostasis (mechanism by which the body maintains adequate calcium levels), acts as a free radical scavenger (Norris et al, 2005), and is known to be involved with calcium ion regulation in the inner ear (William, 2007).

Recent research has shown that four genes involved in skin pigmentation show clear evidence of selection in Europeans (OCA2, MYO5A, DTNBP1, TYRP1). All four genes are associated with Mendelian disorders that cause lighter pigmentation or albinism, and all are in different genomic locations, indicating the action of separate selective events (Voight et al, 2006). One of these genes, “OCA2”, is associated with the third longest haplotype on a high frequency SNP anywhere in the genome for Europeans. A fifth gene, “SLC24A5”, has recently been shown by another group to impact skin pigmentation and to have a derived, selected allele near fixation in Europeans (Lamason et al., 2005).

It has also been shown that Caucasians have higher concentrations of a more deleterious form of melanin known as “Pheomelanin.” The type of melanin that causes blonde and red hair actually increases the risk for cell death. Melanin filters out UV radiation, but it also increases UV harmful effects and causes cell death, particularly when the melanin is the kind found in light hair or skin (Brash et al., 2004). The resulting sunlight sensitivity of individuals with any particular melanin type would reflect the balance between protection and damage, with pheomelanin contributing 3-fold greater damage than eumelanin and perhaps less efficient protection (ibid). In this scenario, when a pheomelanin-containing individual visits the beach, his melanosomes act as microscopic x-ray sources to generate superoxide and OH_ radicals. Pheomelanin also produces almost five times as much superoxide as eumelanin after UV exposure (Persad et al, 1983).

Melanin is also said to play an important role in vision. James Norris Jr., Professor in Chemistry, and retina surgeon Kourous Rezaei, Director of the Vitreoretinal Service in Ophthalmology & Visual Science, combined resources to show that melanin, a pigment found throughout the human body, acts like a neutralizing sponge inside cells in the retina to soak up and destroy reactive oxygen species. Reactive oxygen species, or free radicals, which are energized by light, are thought to play a major role in “macular degeneration”, the leading cause of blindness in people over the age of 60. The disorder is far more prevalent among whites than among African-Americans. It causes gradual loss of central vision by damaging the RPE (retinal pigment epithelial) cells that lie underneath the macula, the small region of the retina responsible for fine detail at the center of the field of vision (See, Norris et al, 2005).

Dark eyes, “in general”, are known to absorb UV better than blue or green (common among Europeans). Melanin provides protection to the lens of the eye from UV damage- decreasing the risks of cataracts. It also provides near optimum protection to the retina and reduces the risk of macular degeneration, as mentioned above. Glare is reduced in dark eyes; and, thus, vision is enhanced.

TADOKORO et al. (2003) for the first time reported the effects of melanin on UV responses in different racial/ethnic groups. DNA damage in all subjects was greatest immediately after UV exposure and was gradually repaired thereafter. Rates and efficiencies of removal of DNA lesions differed dramatically between subjects in all groupings, but DNA damage was most severe in the light skin. The overall finding was that melanin affords significant protection against DNA damage in underlying skin cells, a concept previously supported by tissue culture and organ model systems. They also found that Melanin can absorb UV efficiently at most wavelengths; an important consideration was whether the protective benefits of melanin derive solely from its function as an optical filter.
References

Brash D.E., Takeuchi S., Zhang W., Wakamatsu K, Ito S., Hearing V.J. Kraemer K.H., (2004).

Melanin acts as a potent UVB photosensitizer to cause an atypical mode of cell death in murine skin. PNAS October 19, 2004 vol. 101 no. 42.

Lamason RL, Mohideen M, Mest JR, Wong AC, Norton HL, et al. (2005) SLC24A5, a putative cation exchanger, affects pigmentation in zebrafish and humans. Science 310:1782–1786.

Norris J. R. , Brandon-Luke L. Seagle, Kourous A. Rezai, Yasuhiro Kobori, Elzbieta M. Gasyna, and Kasra A. Rezaei (2005) Melanin photoprotection in the human retinal pigment epithelium and its correlation with light-induced cell apoptosis. PNAS June 21, 2005 vol. 102 no. 25.

Persad, S., Menon, I. A. & Haberman, H. F. (1983) Photochem. Photobiol. 37, 63–68.

TADOKORO T., KOBAYASHI N., ZMUDZKA B.Z., ITO S., WAKAMATSU K., YAMAGUCHI Y., KOROSSY
K. S., MILLER S. A., BEER J.Z., AND HEARING V. J.(2003). UV-induced DNA damage and melanin content in human skin differing in racial/ethnic origin. The FASEB Journal Vol. 17 June 2003 pages 1177-1179.

Voight BF, Kudaravalli S, Wen X, Pritchard JK (2006) A map of recent positive selection in the human genome. PLoS Biol 4(3): e72.

William B. (2007). Quantification of Ca2+ binding to melanin supports the hypothesis that melanosomes serve a functional role in regulating calcium homeostasis. Pigment Cell Research. 20(2):134-139, April 2007.

[Djedi Maaur]

Whites Are Genetically Inferior Print E-mail
Saturday, 15 March 2008
Drawing on 935 individual samples from the French databank, a Stanford University team found deep traces of long-ago population movements, all originating from a “ground zero” in Ethiopia, Kenya or Tanzania. For example, the Pygmies of the Congo forest were found to be quite close to the Bushmen of Namibia — but both were very different from most other sub-Saharan groups. The fierce and proud Bedouin nomads of the Middle East actually have a lot of European and South Asian blood. The Asian-looking Hazara of Afghanistan are correct in claiming ancestry in Mongolia, but the Han, the dominant ethnic group in China, may be disappointed to discover they’re actually two peoples, one north, the other south. Native Americans have at least one closely related group in Asia — the Yakuts of eastern Siberia, who themselves are related to other hunter-gatherer Siberian tribes, some of whom build wooden teepees.
Whites Genetically Weaker Than Blacks, Study Finds

Fox News (February 22, 2008)

“White Americans are both genetically weaker and less diverse than their black compatriots, a Cornell University-led study finds.

Analyzing the genetic makeup of 20 Americans of European ancestry and 15 African-Americans, researchers found that the former showed much less variation among 10,000 tested genes than did the latter, which was expected.

They also found that Europeans had many more possibly harmful mutations than did African, which was a surprise.

“Since we tend to think of European populations as quite large, we did not expect to see a significant difference in the distribution of neutral and deleterious variation between the two populations,” said senior co-author Carlos Bustamante, an assistant professor of biological statistics and computational biology at Cornell.

It’s been known for years that all non-Africans are descended from a small group, perhaps only a few dozen individuals, who left the continent between 50,000 and 100,000 years ago.

But the Cornell study, published in the journal Nature Thursday, indicates that Europeans went through a second “population bottleneck,” probably about 30,000 years ago, when the ancestral population was again reduced to relatively few in number.

The doubly diluted genetic diversity has allowed “bad” mutations to build up in the European population, something that the more genetically varied African population has had more success in weeding out.

“What we may be seeing is a ‘population genetic echo’ of the founding of Europe,” said Bustamante.

The Cornell team hopes to study other population groups in search of similar results.

For example, Native Americans show even less genetic diversity than Europeans, having descended from a few thousand people who entered North America about 10,000 years ago.

That fact was reinforced by a larger-scale study, also published in Nature, led by scientists from the Universities of Michigan and Virginia who analyzed genetic samples of 485 individuals scattered around the globe whose DNA is recorded in a French databank.

As would be expected with the “out of Africa” theory, the researchers found Africans had the greatest amount of genetic diversity, followed in turn by Middle Easterners, then Europeans and South Asians at about equal levels, then East Asians.

Native Americans had the least genetic diversity of all, indicating that part of the world was settled last.

“Previously, we’ve been able to look at the genome and say, ‘This part is from Africa, this is from Asia,’” explained Virginia research Andrew Singleton to Wired News. “Now we can look past that and say, ‘It’s from this part of Africa or Eurasia.’”

A third study, published in the journal Science on Friday, may be the most fascinating of all.

Drawing on 935 individual samples from the French databank, a Stanford University team found deep traces of long-ago population movements, all originating from a “ground zero” in Ethiopia, Kenya or Tanzania.

For example, the Pygmies of the Congo forest were found to be quite close to the Bushmen of Namibia — but both were very different from most other sub-Saharan groups.

The fierce and proud Bedouin nomads of the Middle East actually have a lot of European and South Asian blood.

The Asian-looking Hazara of Afghanistan are correct in claiming ancestry in Mongolia, but the Han, the dominant ethnic group in China, may be disappointed to discover they’re actually two peoples, one north, the other south.

Native Americans have at least one closely related group in Asia — the Yakuts of eastern Siberia, who themselves are related to other hunter-gatherer Siberian tribes, some of whom build wooden teepees.

The Basques in northeastern Spain and southwestern France may be right to demand their own nation — they’re not closely related to anyone else. Surprisingly, neither are the residents of Sardinia off the coast of Italy.

As with the other large-scale study, the Stanford team found the greatest diversity outside of Africa among people living in the wide crescent of land stretching from the eastern shore of the Mediterranean to northern India.

Not only was the region among the first colonized by the African migrants, they theorize, but the large number of European and East Asian genes among the population indicates that it’s long been the human highway, with large numbers of migrants from both directions conquering, trading and generally reproducing along its entire length.”
References

www.nature.com/nature/journal/v451/n7181/full/nature06611.html

www.foxnews.com/story/0,2933,331949,00.html

www.washingtonpost.com/wp-dyn/content/article/2008/02/21/AR2008022102739_2.html

www.news.cornell.edu/stories/Feb08/BustamanteAA.kr.html

blog.wired.com/wiredscience/2008/02/studies-put-pop.html

www.mercurynews.com/peninsula/ci_8332961?nclick_check=1

Originally appeared on FoxNews.com

[Djedi Maaur]

Pale and Black Genes Print E-mail
Saturday, 15 March 2008
The marauding Mongols left not just a huge cultural and historical impression in central Asia, but also a genetic one. For instance, the Hazara people of central Afghanistan share genetic ties with East Asia.Silk Route traders left their own mark. The Uighur, a Muslim minority in northwest China, share genes with people in Europe and west Asia.
Tracing Human Diversity Through the Ages

Stanford Scientists Find Surprising Links

By Lisa M. Krieger (Feburary 22, 2008)


The data also bolsters the prevalent "Out of Africa" theory that humans emerged from the sub-Sahara, perhaps Ethiopia or Tanzania, then colonized the world in several waves.


A coalition of Stanford scientists has released the most detailed road map yet of human diversity, offering insight into the emergence and restless migration of the world's populations.

Using the Stanford Human Genome Center to study genetic variations in almost 1,000 individuals from 51 populations, the team has completed the largest analysis to date of human diversity. The data is published in today's issue of the journal Science.

The scientists discerned some of the great sweeps of human movement, like the early exodus out of Africa. They also found evidence of more recent micro-migrations by groups like American Indians, Silk Route traders and the Mongol invasion led by Genghis Khan.

"This is the definitive study to show variation within populations," said Marcus Feldman, professor of biological sciences and a member of the team.

"During the long historical migrations, people have left genes along the way," said Feldman, who has spent decades studying human genetic diversity, along with co-author Luca Cavalli-Sforza, a professor emeritus of genetics.

They grouped people according to their similarities at 650,000 locations on their DNA - a far higher level of precision than in previous studies.

"We were able to get a picture of the genetic differences and similarities in these people in much greater detail than before," said senior author Richard Myers, professor of genetics.

For instance, the team found that:

Political separatist groups, such as the Basques, Sardinians and the Adygey from the north Caucasus Mountains of Russia, are genetically distinct - not just culturally and politically different - from their surrounding populations.


A group of Russian people called the Yakuts, native to the cold, dry tundra of Siberia, share genetic similarities with people indigenous to South and Central America - such as the Mayans, the Pima and even the Surui of the Brazilian jungles. This supports theories about human migration from Siberia across the Bering Strait to the Americas.


Chinese fall into northern and southern groups. People who live along the northern border near Mongolia are genetically distinct from the Han Chinese of the southern part of the nation.


Middle Eastern populations show multiple sources of ancestry.


For example, the largely Pakistani populations of Burusho, Pashtuns and Sindhi can trace their genetic roots to East Asia. The Palestinians, Bedouin and Druze carry genes also found in Europe and South/Central Asia.

"This tells us that the Middle East has long been a center of migration - that people have been passing through there and leaving genes as they go, either from east or from the west," Feldman said.

The marauding Mongols left not just a huge cultural and historical impression in central Asia, but also a genetic one. For instance, the Hazara people of central Afghanistan share genetic ties with East Asia.

Silk Route traders left their own mark. The Uighur, a Muslim minority in northwest China, share genes with people in Europe and west Asia.

The data also bolsters the prevalent "Out of Africa" theory that humans emerged from the sub-Sahara, perhaps Ethiopia or Tanzania, then colonized the world in several waves.

The Stanford work is based on the fact that genetic material is rigidly passed down from parents to children. But along the way, there are errors, mostly harmless, called mutations, that arise when the DNA is erroneously copied during cell division. They occur at a constant rate.

Genome Center magnifying tools made it possible to study these very tiny genetic mutations, called polymorphisms. Mathematical analysis of the mutations - looking at differences and similarities between populations - creates a historical map of human migration.

In the future, they hope to have access to samples from even more populations, adding to the map.

Originally appeared in Mercury News.