Maps of mitochondrial DNA, Y-chromosome and tyrosinase variation in Eurasian and Oceanian populations
Date
2013-10-09
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Abstract
Teades liikide DNA järjestuste erinevusi, saame rekonstrueerida nende genealoogilisi sidemeid. Selline metodoloogia on laialt kasutusel kaasaegse inimese eelajaloo uurimisel. Haploidse mitokondriaalse DNA ja Y-kromosoomi uuringud näitavad, et meie esivanemad tekkisid Aafrikas umbes 200 000 aastat tagasi, kust asustasid teised maailmajaod. Käesolevas töös analüüsiti haploidsed genoomilookuseid eesmärgiga valgustada Austraalia ja Uus-Guinea eelajalugu. Pleistotseeni ajal moodustasid need kaks piirkonda ühtse kontinendi – Sahuli. Vaatama sellele, et kaasaegse inimese arheoloogilised jäljed Sahulis on ühed vanimad Euraasias, on meie teadmised piirkonna asustamisest lünklikud. Antud uurimuse tulemused on kooskõlas arheoloogiste andmetega, mis näitavad, et piirkond oli asustatud umbes 50 000 aastat tagasi. Peale algset asustamist oli Austraalia ja Uus-Guinea põlispopulatsioonide omavaheline geneetiline kontakt väga piiratud ning austraallased olid oma evolutsiooni jooksul tugevas isolatsioonis. Uus-Guinea põlispopulatsioonidel oli holotseeni keskel sidemeid Kagu-Aasia rahvastega.
Doktoritöö teine osa on pühendatud inimpopulatsioonide nahavärvi erinevuste uuringutele. Selle eesmärgi saavutamiseks analüüsiti varieeruvust TYR geenis, mis kodeerib nahapigmendi melaniini tootmises keskset ensüümi – türosinaasi. Melaniini põhifunktsioon on kaitse kahjuliku UV-kiirguse vastu. Eurooplastele on iseloomulikud mitte-sünonüümsed mutatsioonid, mis vähendavad türosinaasi aktiivsust. Meie dateeringud näitavad, et selliste mutatsioonide teke eurooplaste eelpopulatsioonis jäi viimase jääaja maksimumi ja sellest hilisemasse aega. See hinnang klapib heledat nahavärvust tagavate mutatioonide ilmumisega teistes pigmentatsiooni geenides Euroopas. Mitte-sünonüümsete polümorfismide levik sai võimalikuks suurematel laiuskraadidel, tagades efektiivsemat vitamiin D tootmist siinses UV-vaeses keskkonnas. Samas puuduvad Euroopa-spetsiifilised mutatsioonid Ida-Aasia rahvastel, mis viitab heleda nahavärvi sõltumatule evolutsioonile. Lisaks ei ole türosinaasi efektiivsust vähendavaid mutatsioone leitud Aafrikas, kuna sealse kõrge UV-kiirguse taseme tõttu takistab looduslik valik taoliste polümorfismide levikut.
Analysis of extant DNA variation is widely used in evolutionary studies of anatomically modern humans. Haploid mtDNA and Y-chromosome research show that our ancestors originated in Africa about 200 thousand years ago and colonized other continents after the Out-of-Africa migration. The first part of the given thesis concentrates on the study of modern haploid variation in aboriginal populations of Australia and New Guinea – inhabitants of prehistoric Sahul continent. Despite the fact that traces of anatomically modern humans in Sahul are among the oldest outside of Africa, our knowledge of prehistory of this area is rather scarce. Results of this study is concordant with the evidence for 50 thousand years old occupation of Sahul and show that after the initial colonization genetic contact between Aboriginal Australians and New Guineans was very limited. Moreover, while Aboriginal Australians were heavily isolated from neighboring Asian populations, population of New Guinea experienced mid-Holocene gene flow from southeastern Asia. The second part of the given thesis addresses the genetic basis of skin color difference among modern human populations by analyzing variation within tyrosinase (TYR) gene. Tyrosinase plays central role in the production of skin photoprotective pigments – melanins. The evolutionary model of human skin pigmentation indicates that our skin should be dark enough (i.e. heavily melanized) to protect from high level of damaging UV radiation near the Equator, but light enough to permit for UV-dependent vitamin D biosynthesis at higher geographical latitudes, e.g. Europe and East Asia. Current results show that Europeans bear an excess of non-synonymous substitutions leading to the decreased tyrosinase activity, while sub-Saharan Africans are virtually depleted of this kind of variation. The age of European-specific alleles postdate the split between Western and Eastern Eurasian populations and support the timeframe for European skin depigmentation, which was proposed from the analyses of other pigmentation genes. In addition, populations of East Asia similarly lack non-synonymous TYR alleles, pointing to the parallel evolution of light skin in Eurasia.
Analysis of extant DNA variation is widely used in evolutionary studies of anatomically modern humans. Haploid mtDNA and Y-chromosome research show that our ancestors originated in Africa about 200 thousand years ago and colonized other continents after the Out-of-Africa migration. The first part of the given thesis concentrates on the study of modern haploid variation in aboriginal populations of Australia and New Guinea – inhabitants of prehistoric Sahul continent. Despite the fact that traces of anatomically modern humans in Sahul are among the oldest outside of Africa, our knowledge of prehistory of this area is rather scarce. Results of this study is concordant with the evidence for 50 thousand years old occupation of Sahul and show that after the initial colonization genetic contact between Aboriginal Australians and New Guineans was very limited. Moreover, while Aboriginal Australians were heavily isolated from neighboring Asian populations, population of New Guinea experienced mid-Holocene gene flow from southeastern Asia. The second part of the given thesis addresses the genetic basis of skin color difference among modern human populations by analyzing variation within tyrosinase (TYR) gene. Tyrosinase plays central role in the production of skin photoprotective pigments – melanins. The evolutionary model of human skin pigmentation indicates that our skin should be dark enough (i.e. heavily melanized) to protect from high level of damaging UV radiation near the Equator, but light enough to permit for UV-dependent vitamin D biosynthesis at higher geographical latitudes, e.g. Europe and East Asia. Current results show that Europeans bear an excess of non-synonymous substitutions leading to the decreased tyrosinase activity, while sub-Saharan Africans are virtually depleted of this kind of variation. The age of European-specific alleles postdate the split between Western and Eastern Eurasian populations and support the timeframe for European skin depigmentation, which was proposed from the analyses of other pigmentation genes. In addition, populations of East Asia similarly lack non-synonymous TYR alleles, pointing to the parallel evolution of light skin in Eurasia.
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Keywords
populatsioonigeneetika, mütokondriaalne DNA, Y-kromosoom, pigmentatsioon, türosinaasid, paleoantropoloogia, population genetics, mitochondrial DNA, pigmentation, tyrosinases, paleoantrophology