عرض مصدر Amelogenin

{{infobox protein
|Name=[[AMELX|amelogenin, X-linked]]
|caption=
|image=
|width=
|HGNCid=461
|Symbol=[[AMELX]]
|AltSymbols=AMG, AIH1
|EntrezGene=265
|OMIM=300391
|RefSeq=NM_001142
|UniProt=Q99217
|PDB=
|ECnumber=
|Chromosome=X
|Arm=p
|Band=22.3
|LocusSupplementaryData=-p22.1
}}
{{infobox protein
|Name= [[AMELY|amelogenin, Y-linked]]
|caption=
|image=
|width=
|HGNCid=462
|Symbol=[[AMELY]]
|AltSymbols=AMGL
|EntrezGene=266
|OMIM=410000
|RefSeq=NM_001143
|UniProt=Q99218
|PDB=
|ECnumber=
|Chromosome=Y
|Arm=p
|Band=11
|LocusSupplementaryData=
}}
'''Amelogenin''' is the name for a series of closely related [[protein]]s involved in [[amelogenesis]], the development of [[tooth enamel|enamel]].<ref>{{MeshName|Amelogenin}}</ref>  They are a type of [[Extracellular matrix|extracellular matrix (ECM)]] protein, which, together with [[ameloblastin]]s, [[enamelin]]s, and [[tuftelin]]s direct the mineralization of enamel to form a highly organized matrix of [[enamel rod|rods]], interrod crystal, and protein.  Although the precise role of amelogenin(s) in regulating the [[mineralization (biology)|mineralization]] process is unknown, it is known that amelogenins are abundant during amelogenesis.  Developing human enamel contains about 30% protein, 90% of which are amelogenins.

== Function ==
Amelogenins are believed to be involved in the organizing of [[enamel rod]]s during [[tooth development]]. The latest research indicates that these proteins regulate the initiation and growth of [[hydroxyapatite]] crystals during the mineralization of enamel. In addition, amelogenins appear to aid in the development of [[cementum]] by directing cementoblasts to the tooth's root surface.

== Variants ==
The amelogenin [[gene]] has been most widely studied in humans, where it is a single copy gene, located on the [[X chromosome|X]] and [[Y chromosome]]s at Xp22.1-Xp22.3 and Yp 11.2 [5].<ref name="pmid2004775">{{cite journal |vauthors =Nakahori Y, Takenaka O, Nakagome Y |url= |format=|title=A human X-Y homologous region encodes "amelogenin" |journal=Genomics. |volume=9 |issue=2 |pages=264–9 |year=1991|pmid=2004775 |doi=10.1016/0888-7543(91)90251-9}}</ref>  The amelogenin gene’s location on sex chromosomes has implications for variability both between the X chromosome form ([[AMELX]]) and the Y chromosome form ([[AMELY]]), and between alleles of AMELY among different populations.  This is because AMELY exists in the [[genetic recombination|non-recombining]] region of chromosome Y, effectively isolating it from normal [[selection pressure]]s.  Other sources of amelogenin variation arise from the various [[protein isoform|isoforms]] of AMELX obtained from alternative splicing of mRNA transcripts.  Specific roles for isoforms have yet to be established.  Among other organisms, amelogenin is well conserved among [[eutheria]]ns, and has homologs in [[monotreme]]s, reptiles and amphibians.

== Application in sex determination ==
Differences between the [[X chromosome]] and [[Y chromosome]] versions of the amelogenin gene (AMELX and AMELY respectively) enable it to be used in sex determination of unknown human samples.  [[AMELX]]’s intron 1 contains a 6 bp deletion relative to [[intron]] 1 of [[AMELY]].  This can be detected at low cost using Polymerase Chain Reaction ([[PCR]]) of intron 1, followed by [[gel electrophoresis]].  Two [[amplicon|bands]] of DNA, at 106bps and 112bps, are resolved if both the AMELX and AMELY versions of the gene are present (i.e. the sample is from a male) or one band of DNA, at 106bps, if the AMELX version only is present (i.e. the sample is from a female).<ref name="pmid16603093">{{cite journal | vauthors = Kashyap VK, Sahoo S, Sitalaximi T, Trivedi R |title = Deletions in the Y-derived amelogenin gene fragment in the Indian population | journal = BMC Med Genet. | volume = 7 | pages = 37 | year = 2006 | pmid = 16603093 | doi =10.1186/1471-2350-7-37 | pmc = 1458324 }}<!--|accessdate= 2008-07-07--></ref> 
 
However because of [[AMELY]] variation among individuals and populations, this method of sex determination is not 100% accurate.  Mutation in regions of AMELY intron 1 commonly used as [[nucleic acid thermodynamics|primer annealing sites]] may disable PCR amplification.  A 6bp [[indel|insertion]] to AMELY intron 1 results in an amplicon identical in length to that of AMELX.  In some males AMELY may be deleted entirely.  In any of these cases only one band is visualized during gel electrophoresis of PCR products, causing misidentification of the sample as female.<ref name="pmid16603093"/> The misidentification rate may vary among populations, but in general appears to be low. In one study in Spain, the amelogenin sex determination test using AMELX (977bps) and AMELY (790bps) bands was performed for 1224 individuals of known gender with a 99.84% (1222/1224) accuracy rate.<ref name="pmid17716640">{{cite journal |vauthors =Francès F, Portolés O, González JI, Coltell O, Verdú F, Castelló A, Corella D |url= |format=|title=Amelogenin test: From forensics to quality control in clinical and biochemical genomics. |journal=Clin Chim Acta |volume=386 |issue=1–2 |pages=53–6|year=2007|pmid=17716640 |doi=10.1016/j.cca.2007.07.020}}</ref>  Another study in India, however, found 5 of its 270 men studied (1.85%) possessed an AMELY deletion, terming them “deleted-amelogenin males” (DAMs). In response the authors suggested that while the amelogenin sex test may be accurate in general, other Y chromosome markers such as [[SRY]], STR, or 50f2 can be used for less ambiguous gender identification.<ref name="pmid12056520">{{cite journal |vauthors =Thangaraj K, Reddy AG, Singh L |url= |format=|title=Is the amelogenin gene reliable for gender identification in forensic casework and prenatal diagnosis? |journal=Int J Legal Med |volume=116 |issue=2 |pages=121–3|year=2002|pmid=12056520|doi=10.1007/s00414-001-0262-y}}</ref>

== Clinical significance ==

Mutations in AMELX can cause [[amelogenesis imperfecta]], a disorder of tooth enamel development.<ref name="pmid16838342">{{cite journal | author = Wright JT | title = The molecular etiologies and associated phenotypes of amelogenesis imperfecta | journal = American Journal of Medical Genetics Part A | volume = 140 | issue = 23 | pages = 2547–55 |date=December 2006 | pmid = 16838342 | pmc = 1847600 | doi = 10.1002/ajmg.a.31358 | url = | issn = }}</ref>

== References ==
{{reflist}}

[[Category:Human proteins]]
[[Category:Teeth]]
[[Category:Genetics]]