Download Zebrafish and Skin Color Reference Data

ZebrafishandSkinColorReferenceData
Melanophoresinzebrafishskin:ThepossibleroleofSLC24A5inhumanskincolorwasfirstsuggestedby
agroupofresearchersanalyzingthegenomesofzebrafish.Theywerelookingforgeneswithmutations
thatmightleadtocancer.Oneofthevarietiestheywereanalyzingisknownasthe“golden”mutant.
Wild-TypeZebrafish
goldenMutant
Figure1.a.Atypical(wild-type)zebrafishandb.goldenzebrafishmutant,eachwithinsetshowingthe
melanophorespresentinthefish’sskin(scalebars=5mm;0.5mmininsets).Melanophoresarethe
melanin-containingcellswithinamphibiansandfish.c.–f.Transmissionelectronmicrographs(TEMs)of
themelanophores(c,d)andmelanosomes(organellesfoundinanimalcellsthatarethesitefor
synthesis,storage,andtransportofmelanin)(e,f)intheskinofwild-type(c,e)andgoldenmutant(d,f)
zebrafish.(ImageadaptedfromLamasonetal.2005.Science.310:1782–1786.)
Melanocytesinhumanskin:Thefigurebelowshowsthemelanin-containingmelanosomesassociated
withthreedifferentnaturalskincolors.
Figure2.Imagesshowingtheamountofmelaninandthesizeandnumberofmelanosomesinpeople
withdifferentskincolors.(ImageadaptedfromTheBiologyofSkinColorfilm.)
SLC24A5allelesandallelefrequencies:Withinthegeneataparticularlocation,thereiseitheran
adenine(Aallele)oraguanine(Gallele).Thissingle-nucleotidedifferenceinDNAresultsinaminoacid
111oftheproteinbeinganalaninefortheGalleleandathreoninefortheAallele.Alanineisnonpolar,
andthreonineispolar.ThischangelikelysignificantlyaltersthefunctionoftheSLC24A5protein.
TheGalleleisfarmorecommonamongpeopleofAfricandescentthanamongpeopleofEuropean
descent.Thisdifferenceinallelefrequencyisunusual.Formanyothergenes,WestAfricansand
Europeanshavesimilarallelefrequencies.Peoplewithancestorsfromevenverydistantgeographic
regionshavefarmoregeneticsimilaritiesthandifferences.
Table1.SLC24A5AlleleFrequency
Population
FrequencyoftheSLC24A5Aalleleat
STRlocusrs1426654
Europeans
0.96(96%)
WestAfricans
0.09(9%)
SLC24A5genotypesandphenotypedistribution:Scientistsmeasuredtherelativeamountofmelaninin
agroupofpeopleofbothAfricanandEuropeanancestrieswitharangeofskincolors.Themelanindata
werethensortedbytheindividuals’genotypeforSLC24A5andrepresentedinthegraphsbelow.
LighterSkinDarkerSkin
Figure3.AmountofmelaninversusgenotypefortheSLC24A5gene.Ahigher“Δmelaninindex”value
meansthattheindividualhaddarkerskin.(ImageadaptedfromLamasonetal.2005.Science.310:1782–
1786.)
AminoacidscodedforbySLC24A5indifferentspecies:ResearchersdeterminedtheDNAsequenceof
themutatedgenethatresultsingoldenzebrafish.Theythensequencedthesamegeneinalarge
numberofothervertebrates,includinghumans.Theresearchersquicklyrecognizedthatthezebrafish
SLC24A5genewasverysimilartotheoneinhumans.SomeoftheaminoacidscodedforbytheSLC24A5
geneareshownbelowforavarietyofspecies.
Figure4.MuchofthissmallsectionoftheproteinencodedbytheSLC24A5geneisthesameacross
severalspecies(showninblack).Eachofthe20aminoacidsfoundinhumansisassigneditsownonelettercode.Forexample,Astandsforalanine.Inhumans,asingle-nucleotidechange(fromGtoA)ata
particularlocusinthegenechangestheresultantaminoacidfromalanine(A)tothreonine(T).The
SLC24A5geneislargerthantheregionshownabove.Recallthatthegoldenphenotypeinzebrafishis
alsocausedbyachangeintheSLC24A5gene,butitistheresultofadifferentmutation.Themutation
thatcausesthegoldenphenotypeinzebrafishislocatedfartherupstreamoftheaminoacidsshown.
(ImageadaptedfromLamasonetal.2005.Science.310:1782–1786.)
TransplantedmRNA:ResearchersmadeamessengerRNA(mRNA)fragmentfromthehumanDNA
sequencefortheSLC24A5Gallele.ThishumanmRNAwasinjectedintogoldenzebrafishembryoswhere
itwastranslatedintoaprotein.Theresearchersthencomparedtheembryotowild-typezebrafishand
goldenzebrafish.Theresultsareshownbelow.
“Golden”zebrafishlarvae
injectedwithhumanmRNA
fromSLC24A5
Wild-typezebrafishlarvae
“Golden”zebrafishlarvae
Figure5.Zebrafishembryosshowingdifferingamountsofmelanin.Notethatpigmented
melanophoresinlarvaeappearasdarkpatchesonthehead,back,andthroughouttheirlargeeyes.
ThemessengerRNA(mRNA)transcribedfromthehumanSLC24A5genewasinjectedintothefishon
theleft.(ImageadaptedfromLamasonetal.2005.Science.310:1782–1786.)
Partialvertebratephylogeny:Thezebrafishisaray-finnedfish.Allray-finnedfishaswellasall
reptiles(andbirds),amphibians,andmammalshavetheSLC24A5gene.Thefigurebelowshowsa
phylogenyofthesegroupsbasedonfossilsandsequencesfromotherregionsofDNA.
Figure6.Aphylogenyforsomeofthemajorgroupsofvertebrates.Branchlengthsareproportionalto
time.Note:“mya”means“millionsofyearsago.”
Indigenousskincolorthroughouttheworld:NinaJablonskiandGeorgeChaplincollaboratedonamapthatshows
hownatural(untanned),indigenous(native)skincolorvariesthroughouttheworld.
ArcticCircle
Tropicof
Cancer
Equator
Tropicof
Capricorn
Figure7.Mapoftheworldcoloredtoshownatural,indigenousskincolor.(ImageadaptedfromTheBiologyofSkin
Colorfilm.)
SLC24A5allelefrequenciesinpopulationsaroundtheworld:ThemapbelowshowstherelativefrequenciesoftheG
andAallelesfortheSLC24A5gene.Eachcirclerepresentsadistinctgroupofpeople.Thelocationofthecircle
correspondstotheancestraloriginofthepopulation.HighfrequenciesoftheGalleleareshownwithincreasing
amountsofblack.(NodataisavailableforAustraliaandmuchofNorthandSouthAmerica.)
Figure8.MapshowingfrequenciesofthetwoallelesforSLC24A5amongancestralpopulationsaroundtheworld.Each
populationisrepresentedbyacirclefilledinproportionallyaccordingtoallelefrequency.TheGalleleiscodedblackand
theAallelegray.Thenumberedpopulationscorrespondtothefollowing:1)Biakapygmies,2)Mbutipygmies,3)
Mandenka,4)Yoruba,5)BantuN.E.,6)San,7)BantuS.E.,8)BantuS.W.,9)Mozabite,10)Bedouin,11)Druze,12)
Palestinian,13)Brahui,14)Balochi,15)Hazara,16)Makrani,17)Sindhi,18)Pathan,19)Kalesh,20)Burusho,21)Han,
22)Tujia,23)Yizu,24)Miaozu,25)Orogen,26)Daur,27)Mongola,28)Hezhen,29)Xibo,30)Uygur,31)Dai,32)Lahu,
33)She,34)Naxi,35)Tu,36)Yakut,37)Japanese,38)Cambodian,39)Papuan,40)NANMelanesian,41)French,42)
FrenchBasque,43)Sardinian,44)NorthernItalian,45)Tuscan,46)Orcadian,47)Adygei,48)Russian,49)Pima,50)
Maya,51)Columbian,52)Karitiana,53)Surui.(ImageadaptedfromNortonetal.2007.Mol.Biol.Evol.24:710–722.)