Evolutionary biology - Geography and skin colour
ABSTRACT Human skin comes in many different shades. Recent studies of geographical differences in skin colour open up the subject scientifically by offering sophisticated accounts of the basis of this variation.
- SourceAvailable from: Marty O. Visscher
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- "Thus, despite the cytotoxic features of melanin or its precursors (Graham et al., 1978), melanosomes are beneficial to cells. Individuals whose ancestors resided more recently in lower-latitude areas tend to have darker skin color, whereas individuals whose ancestors resided more recently in higher-latitude areas tend to have relatively lighter skin color (Jablonski and Chaplin, 2000; Diamond, 2005). At higher latitudes, the toxicity of melanosomes may be a more important consideration than their photoprotective function; from this perspective, populations living in higher latitudes may no longer need to retain melanosomes. "
ABSTRACT: Melanin in the epidermis determines the wide variation in skin color associated with ethnic skin diversity. Ethnic differences exist regarding melanosome loss in keratinocytes, but the mechanisms underlying these differences, and their contribution to the regulation of skin color, remain unclear. Here we explored the involvement of autophagy in determining skin color by regulating melanosome degradation in keratinocytes. Keratinocytes derived from Caucasian skin exhibit higher autophagic activity than those derived from African-American skin. Furthermore, along with the higher autophagy activity in Caucasian skin-derived keratinocytes compared to African-American skin-derived keratinocytes, Caucasian-derived keratinocytes were more sensitive to melanosome treatment as shown by their enhanced autophagic activity, that may reflect the substantial mechanisms in human epidermis due to the limitations of the models. Melanosome accumulation in keratinocytes was accelerated by treatment with lysosomal inhibitors or with siRNAs specific for autophagy-related proteins which are essential for autophagy. Furthermore, consistent with the alterations in skin appearance, the melanin levels in human skin cultured ex vivo and in human skin substitutes in vitro were substantially diminished by activators of autophagy and enhanced by the inhibitors. Taken together, our data reveal that autophagy plays a pivotal role in skin color determination by regulating melanosome degradation in keratinocytes, and thereby contributes to the ethnic diversity of skin color.Journal of Investigative Dermatology accepted article preview online, 4 April 2013; doi:10.1038/jid.2013.165.Journal of Investigative Dermatology 04/2013; 133(10). DOI:10.1038/jid.2013.165 · 7.22 Impact Factor
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- "People whose ancestors originated from lower latitude areas tend to have darker skin color, whereas people whose ancestors were from higher latitude areas tend to have relatively lighter skin color, indicating that human skin color is one of the characteristics evolutionarily and geographically acquired to protect the skin from harmful ultraviolet radiation , . Regarding such correlations, the Fitzpatrick Scale, which represents fair skin people to always or usually sunburn (Types I and II) and dark skin people to be only slightly or never sunburned (Types V and VI), was developed in 1975 to classify skin complexion and its tolerance to sunlight among different skin types and has been widely used for dermatologic research . "
ABSTRACT: Human skin color is predominantly determined by melanin produced in melanosomes within melanocytes and subsequently distributed to keratinocytes. There are many studies that have proposed mechanisms underlying ethnic skin color variations, whereas the processes involved from melanin synthesis in melanocytes to the transfer of melanosomes to keratinocytes are common among humans. Apart from the activities in the melanogenic rate-limiting enzyme, tyrosinase, in melanocytes and the amounts and distribution patterns of melanosomes in keratinocytes, the abilities of the actin-associated factors in charge of melanosome transport within melanocytes also regulate pigmentation. Mutations in genes encoding melanosome transport-related molecules, such as MYO5A, RAB27A and SLAC-2A, have been reported to cause a human pigmentary disease known as Griscelli syndrome, which is associated with diluted skin and hair color. Thus we hypothesized that process might play a role in modulating skin color variations. To address that hypothesis, the correlations of expression of RAB27A and its specific effector, SLAC2-A, to melanogenic ability were evaluated in comparison with tyrosinase, using human melanocytes derived from 19 individuals of varying skin types. Following the finding of the highest correlation in RAB27A expression to the melanogenic ability, darkly-pigmented melanocytes with significantly higher RAB27A expression were found to transfer significantly more melanosomes to keratinocytes than lightly-pigmented melanocytes in co-culture and in human skin substitutes (HSSs) in vivo, resulting in darker skin color in concert with the difference observed in African-descent and Caucasian skins. Additionally, RAB27A knockdown by a lentivirus-derived shRNA in melanocytes concomitantly demonstrated a significantly reduced number of transferred melanosomes to keratinocytes in co-culture and a significantly diminished epidermal melanin content skin color intensity (ΔL* = 4.4) in the HSSs. These data reveal the intrinsically essential role of RAB27A in human ethnic skin color determination and provide new insights for the fundamental understanding of regulatory mechanisms underlying skin pigmentation.PLoS ONE 07/2012; 7(7):e41160. DOI:10.1371/journal.pone.0041160 · 3.23 Impact Factor
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- "Journal of Investigative Dermatology advance online publication, 24 November 2011; doi:10.1038/jid.2011.358 Defining the role of natural selection in explaining variation in human skin and hair color is one of the classic problems of human biology (Cavalli-Sforza, 2001; Barsh, 2003; Rees, 2003; Jablonski, 2004; Diamond, 2005; Robins, 2005, 2009; Parra, 2007). Why exactly do humans vary in skin and hair color, and what explains the longstanding correlations between skin pigmentation and geographical and genetic ancestry? "
ABSTRACT: Variation in human skin and hair color is one of the most striking aspects of human variability, and explaining this diversity is one of the central questions of human biology. Only in the last decade or so has it been realistically possible to address this question experimentally using population genetic approaches. On the basis of earlier studies in mice, and on studies in humans with various Mendelian disorders, many of the genes underpinning population variation in skin color have been identified. More recently, genome-wide approaches have identified other loci that appear to contribute to pigmentary variation. The ability to study sequence diversity from world populations has allowed examination of whether the observed variability is due to random genetic drift or is a result of natural selection. The genetic evidence taken as a whole provides strong evidence for natural selection, functioning so as to increase pigment diversity across the world's populations. Future larger studies are likely to provide more details of this process and may provide evidence for exactly which mechanistic pathways have mediated selection.Journal of Investigative Dermatology 11/2011; 132(3 Pt 2):846-53. DOI:10.1038/jid.2011.358 · 7.22 Impact Factor