EDAR and other genes provide instructions for making proteins that work together during embryonic development. These proteins form part of a signaling pathway that is critical for the interaction between two cell layers, the ectoderm and the mesoderm. In the early embryo, these cell layers form the basis for many of the body's organs and tissues. Ectoderm-mesoderm interactions are essential for the proper formation of several structures that arise from the ectoderm, including the skin, hair, nails, teeth, and sweat glands.[3]
A derived G-allele point mutation (SNP) with pleiotropic effects in EDAR, 370A or rs3827760, found in most modern East Asians and Native Americans but not common in African or European populations, is thought to be one of the key genes responsible for a number of differences between these populations, including the thicker hair, more numerous sweat glands, smaller breasts, and the Sinodont dentition (so-called shovel incisors) characteristic of East Asians.[5] It has been hypothesized that natural selection favored this allele during the last ice age in a population of people living in isolation in Beringia, as it may play a role in the synthesis of breast milk under Vitamin D-poor conditions.[6][7][8] The 370A mutation arose in humans approximately 30,000 years ago, and now is found in 93% of Han Chinese and in the majority of people in nearby Asian populations. This mutation is also implicated in ear morphology differences and reduced chin protrusion.[9] The derived G-allele is a mutation of the ancestral A-allele, the version found in most modern non-East Asian and non-Native American populations.
In a 2015 study, three (of six) ancient DNA samples (7,900-7,500 BP) from Motala, Sweden; two (3300–3000 BC) from the Afanasevo culture and one (400–200 BC) Scythian sample were found to carry the rs3827760 mutation.[10]
In a 2018 study, several ancient DNA samples from the Americas, including USR1 from the Upward Sun River site, Anzick-1, and the 9,600 BP individual from Lapa do Santo, were found to not carry the derived allele. This suggests that the increased frequency of the derived allele occurred independently in both East Asia and the Americas.[11]
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Sinha SK, Zachariah S, Quiñones HI, Shindo M, Chaudhary PM (Nov 2002). "Role of TRAF3 and -6 in the activation of the NF-kappa B and JNK pathways by X-linked ectodermal dysplasia receptor". The Journal of Biological Chemistry. 277 (47): 44953–61. doi:10.1074/jbc.M207923200. PMID12270937.
Shu H, Chen S, Bi Q, Mumby M, Brekken DL (Mar 2004). "Identification of phosphoproteins and their phosphorylation sites in the WEHI-231 B lymphoma cell line". Molecular & Cellular Proteomics. 3 (3): 279–86. doi:10.1074/mcp.D300003-MCP200. PMID14729942.
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