I-DNA Methylation ekubonisweni kwezakhi zofuzo
I-DNA methylation ingenye yezindlela ezibaluleke kakhulu ze-epigenetic, elawula ukuthi i-gene ibonakaliswa nini futhi iqine kangakanani ngaphandle kokushintsha ukulandelana kwesisekelo se-DNA uqobo. Ngamanye amazwi, ulwazi lwezakhi zofuzo luhlala lufana, kodwa "ukufunda" kwalo kungashintsha. Le nqubo idlala indima enkulu ekuthuthukisweni kombungu, ukuhlukaniswa kwamaseli, ukugcinwa kobunikazi bezicubu, ngisho nokubandakanyeka kwayo ezifweni ezahlukahlukene njengomdlavuza. Ukuqonda i-DNA methylation kusisiza sibone ukuthi ukulawulwa kwezakhi zofuzo akukhona nje ukuthi yiziphi izakhi zofuzo esinazo, kodwa nokuthi lezo zakhi zofuzo "zisebenza" noma "zithuliswa" kanjani ezimweni ezithile zebhayoloji.
Kuyini i-DNA methylation?
I-methylation ye-DNA iwukungezwa kweqembu le-methyl (–CH₃) ku-molecule ye-DNA. Ezilwaneni ezinomgogodla, lokhu kuguqulwa kuvame ukwenzeka ezisekelweni ze-cytosine kulandelwe yi-guanine (ebizwa ngokuthi izindawo ze-CpG, kusukela ku-“C-phosphate-G”). I-Cytosine ezindaweni ze-CpG ingaxutshwa ne-methyl ibe yi-5-methylcytosine (5mC). Nakuba kubonakala kulula, ukungezwa kwaleli qembu elincane kungashintsha ukusebenzisana kwe-DNA namaprotheni alawula ukuqoshwa kwezakhi zofuzo, ngaleyo ndlela kushintshe amazinga okubonakaliswa kwezakhi zofuzo.
I-methylation ye-DNA iwela ngaphansi kwe-epigenetics ngoba izuzwa njengefa ngesikhathi sokuhlukaniswa kwamaseli (i-mitosis) kodwa iyaguqulwa futhi ayishintshi ukulandelana kwe-nucleotide. Lokhu kusho ukuthi amaseli amabili ane-DNA efanayo—isibonelo, iseli lesibindi neseli lemizwa—angaba namaphethini ahlukene e-methylation abangela ukuthi aveze amasethi ahlukene ezakhi zofuzo.
Ama-enzyme alawula i-methylation: DNMT
Inqubo ye-methylation ayizenzekeli ngokuzenzakalelayo, kodwa kunalokho iqondiswa ama-enzyme e-DNA methyltransferase (DNMT). Ngokuvamile, kunezinhlobo eziningana ezibalulekile ze-DNMT:
1. I-DNMT3A kanye ne-DNMT3B: inesibopho se-de novo methylation, okungukuthi ukwakheka kwamaphethini amasha e-methylation ngesikhathi sokuthuthukiswa kwamaseli okuqala kanye nokwehlukaniswa kwawo.
2. I-DNMT1: idlala indima ekugcinweni kwe-methylation, okungukuthi igcina amaphethini e-methylation ngemva kokuphindaphindwa kwe-DNA ukuze amangqamuzana endodakazi athole ifa "lenkumbulo" ye-epigenetic yeseli lomzali.
Uma i-DNA iphindaphinda, i-methylation ethile "ingalahleka" ngoba i-strand entsha ayina-methyl. I-DNMT1 ibona i-DNA ene-hemimethyl (i-strand endala ine-methylated, i-strand entsha ayinayo) futhi inezela i-methyl ku-strand entsha ukuze iphethini ye-methylation igcinwe.
Ngakolunye uhlangothi, ukususwa kwe-methyl kungenzeka ngezinqubo ezingasebenzi (isb., ukwehluleka kokugcinwa ngesikhathi sokuhlukaniswa kwamaseli) noma ngenkuthalo ngama-enzyme afana nomndeni we-TET (Ten-Eleven Translocation) okhiqiza i-oxidize 5mC futhi ubangele i-DNA repair cascade ukuze kubuyiselwe ama-cytosine angena-methylated.
Ubudlelwano phakathi kwe-DNA methylation kanye nokubonakaliswa kwezakhi zofuzo
Umphumela we-methylation ekubonakalisweni kwezakhi zofuzo uncike kakhulu endaweni ye-methylation ku-genome.
1. I-Methylation ku-promoter: ivame ukuthulisa izakhi zofuzo
I-promoter yisifunda se-DNA eduze kokuqala kwe-gene esisebenza "njengendawo yokuqala" yokubhala. Ama-promoter amaningi ezakhi zofuzo anobuningi obukhulu be-CpGs, okuthiwa iziqhingi ze-CpG. Uma isiqhingi se-CpG ku-promoter sine-methylated, ukubhalwa kwezakhi zofuzo kuvame ukwehla noma kume. Lokhu kwenzeka ngezindlela ezimbili eziyinhloko:
– Ukuvimbela izici zokubhala: ezinye izici zokubhala azikwazi ukubopha kwi-DNA uma izindawo zazo zokuqaphela zixutshwe ne-methyl.
– Ukuqoqa amaprotheni ahlanganisa i-methyl: Amaprotheni afana ne-MeCP2 angabona i-DNA ene-methyl bese eqoqa ama-repressor complexes (isb., i-histone deacetylase/HDAC). Ngenxa yalokho, i-chromatin iba ncane kakhulu (i-heterochromatin), futhi imishini yokubhala inobunzima bokufinyelela izakhi zofuzo.
2. I-Methylation emzimbeni wezakhi zofuzo: ingahlobana nezakhi zofuzo ezisebenzayo
Ngokuthakazelisayo, i-methylation yomzimba wezakhi zofuzo ivame ukutholakala kuma-gene abonakala ngokusebenzayo. Esinye isici ukuthi i-methylation yomzimba wezakhi zofuzo isiza ekuvimbeleni ukuqala kokubhalwa "okungafanele" futhi ithuthukisa ukuthembeka kokubhalwa. Ngakho-ke, i-methylation ayifani ngaso sonke isikhathi nokuthulisa; umongo we-genomic ubalulekile.
3. I-Methylation yezithuthukisi nezinye izakhi zokulawula
Izithuthukisi ziyizakhi ze-DNA ezingakhulisa ukuvezwa kwezakhi zofuzo kude. I-Methylation yezithuthukisi ngokuvamile inciphisa umsebenzi wezithuthukisi, ngaleyo ndlela inciphise ukuvezwa kwezakhi zofuzo okuqondiwe. Ukushintsha kwe-methylation yezithuthukisi kunganikeza indlela esheshayo yokuthi amaseli avumelanise izinhlelo zawo zezakhi zofuzo nezimpawu zokuthuthukiswa noma zemvelo.
I-methylation ye-DNA ekuthuthukisweni nasekuhlukaniseni
Ngesikhathi sokukhula kombungu, kwenzeka "ukuhlelwa kabusha" okukhulu kwamaphethini e-methylation. Esigabeni esithile, i-genomic methylation iyancipha emhlabeni wonke, bese izivuselela ngokwahluka. Le nqubo ivumela amaseli okuqala embungu ukuthi alondoloze ukuguquguquka, bese kancane kancane evala ubunikazi bamaseli awo—isibonelo, amaseli emisipha, amaseli e-epithelial, noma ama-neurons—ngokuthulisa izakhi zofuzo ezingabalulekile emsebenzini wazo.
Isibonelo esilula: izakhi zofuzo ezidingekayo kumaseli ezinzwa zingasebenza ngoba ama-promoter azo awana-methyl eyanele kuma-neuron, kodwa izakhi zofuzo ezifanayo zingathuliswa kumaseli esibindi nge-methylation ye-promoter. Ngakho-ke, i-methylation isiza ukugcina ukuzinza kwesikhathi eside kobunikazi bamaseli.
Ukunyatheliswa kwe-genomic kanye nokungasebenzi kwe-chromosome ye-X
I-methylation ye-DNA ibalulekile futhi ezimweni ezithile ze-epigenetic:
– Ukunyatheliswa kwezakhi zofuzo kuwukubonakaliswa kwezakhi zofuzo okuncike kubazali bazo (bakamama noma bakayise). Kwezinye izakhi zofuzo, i-allele eyodwa ithuliswa nge-methylation, ukuze kuvele i-allele kayise noma kamama kuphela.
– Ukungasebenzi kwe-chromosome X ezincelisayo zesifazane kuyinqubo yokuvala enye yama-chromosome X ukuze kulinganiswe ukusatshalaliswa kwezakhi zofuzo nokwabesilisa. I-Methylation idlala indima ekugcineni lesi simo sokungasebenzi, kanye nokuguqulwa kwe-histone kanye ne-RNA engabhalisi ikhodi.
Lezi zinqubo ezimbili zibonisa ukuthi i-methylation akuyona nje indlela yokulawula ukulungiswa kahle, kodwa kunalokho iyindlela "yokushintsha" engasungula amaphethini azinzile okubonakaliswa kwezakhi zofuzo.
I-DNA methylation kanye nesifo
Izinguquko emaphethini e-methylation zingaphazamisa ukulawulwa kwezakhi zofuzo futhi zibe nomthelela ezifweni.
1. Umdlavuza
Emdlavuzeni, amaphethini amabili abonakala ephikisana avame ukwenzeka ndawonye:
– I-hypomethylation yomhlaba wonke: ukwehla kwe-methylation ezindaweni eziningi ze-genome kungaholela ekungazinzini kwe-genome, ukusebenza kwezinto eziguqulwayo, kanye nokwanda kwezinguquko.
– I-Hypermethylation yabagqugquzeli bezakhi zofuzo ezicindezela isimila: Abagqugquzeli bezakhi zofuzo okufanele bavimbele ukukhula kwamangqamuzana bangaba ne-methyl eningi, bathulise izakhi zofuzo. Ngenxa yalokho, amangqamuzana anganda kalula ngokungalawuleki.
Ngenxa yokuthi i-methylation iyakwazi ukuguqulwa, izindlela zokwelapha ze-epigenetic ezifana ne-DNMT inhibitors ziye zasetshenziswa ezinhlotsheni ezithile zomdlavuza ukuzama "ukuvula" izakhi zofuzo ezithulile.
2. Izinkinga zemizwa kanye nokukhula
Amaprotheni abopha i-DNA e-Methylated njenge-MeCP2 axhunyaniswe nomsebenzi wezinzwa; izinguquko ku-MECP2 zingabangela i-Rett syndrome. Lokhu kusikisela ukuthi incazelo ye-methylation ibaluleke njenge-methylation uqobo.
3. Amathonya emvelo nendlela yokuphila
Ukudla okunempilo (isb., i-folate njengomnikeli we-methyl), ukuchayeka ezintweni ezingcolisayo, ukucindezeleka, nezinye izici zendlela yokuphila kungathonya amaphethini e-methylation. Nakuba ubudlelwano phakathi kwezimbangela nemiphumela kubantu buvame ukuba yinkimbinkimbi, izifundo eziningi ziphakamisa ukuthi indawo ezungezile ingashiya "uphawu lwe-epigenetic" olungaba nomthelela engcupheni yesifo.
I-DNA methylation ifundwa kanjani?
Ucwaningo lwe-DNA methylation luthuthuka ngokushesha ngenxa yobuchwepheshe bokulandelana. Izindlela ezidumile zifaka:
– Ukulandelana kwe-Bisulfite: Ukwelashwa kwe-Bisulfite kuguqula i-cytosine engaxutshwe ne-methyl ibe yi-uracil, kuyilapho i-5mC ihlala njenge-cytosine. Ngokuqhathanisa imiphumela yokulandelana, abacwaningi bangakwazi ukumaka izindawo ze-methylation ngesisombululo esiphezulu.
– I-Methylation array: ilinganisa i-methylation ezindaweni ezingamakhulu ezinkulungwane ze-CpG ngokushesha nangokungacubunguli.
– Ukuhlolwa okusekelwe ku-Methylation okusekelwe ku-PCR: kuyasiza ekuhloleni isimo se-methylation sezakhi zofuzo ezithile, isibonelo ezifundweni ze-biomarker yomdlavuza.
Imiphumela yokulinganisa i-methylation ixhunyaniswa nedatha yokubonakaliswa kwezakhi zofuzo (i-transcriptome) ukuze kuqondwe umthelela wazo wokusebenza.
Isiphetho
I-methylation ye-DNA iyisici esibalulekile sokulawulwa kwe-epigenetic esithonya ukuvezwa kwezakhi zofuzo ngokomongo: ivame ukucindezela izakhi zofuzo uma zenzeka kuma-promoters, kodwa ingaba neminye imisebenzi uma zenzeka emzimbeni wezakhi zofuzo noma ezindaweni ezithuthukisayo. Ngokusebenza kwama-enzyme e-DNMT kanye nezinhlelo ze-demethylation, amaseli angasungula, alondoloze, futhi ashintshe amaphethini okubonakaliswa kwezakhi zofuzo ngokuya ngezidingo zokuthuthukiswa kanye nezimpendulo zemvelo. Lapho lolu hlelo luphazamiseka, ingozi yesifo—ikakhulukazi umdlavuza kanye nezinkinga zokukhula—inganda. Ngenxa yemvelo yalo enamandla futhi engase iguqulwe, i-methylation ye-DNA akuyona nje isihloko esiyisisekelo ku-biology yamangqamuzana kodwa futhi iyinsimu ethembisayo yokuxilonga nokwelapha okusekelwe ku-epigenetic.
Uma ufisa, ngingaguqula lesi sihloko sibe inguqulo yezemfundo (enezingcaphuno kanye namagama obuchwepheshe) noma inguqulo ethandwayo yabafundi abavamile.
