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38 Îáçîðû Ìîëåêóëÿðíûé êîíòðîëü ïëþðèïîòåíòíîñòè À.Ñ. Ãðèãîðÿí, Ï.Â. Êðóãëÿêîâ ÎÎÎ «Òðàíñ-Òåõíîëîãèè», Ñàíêò-Ïåòåðáóðã Molecular control of pluripotency A.S. Grigorian, P.V. Kruglyakov Trans-Technologies Ltd., Saint-Petersburg Ýìáðèîíàëüíûå ñòâîëîâûå êëåòêè (ÝÑÊ) çà ñ÷åò ñâîèõ óíèêàëüíûõ ñâîéñòâ (ñàìîîáíîâëåíèÿ ïîïóëÿöèè è ïëþðèïîòåíòíîñòè), îáëàäàþò áîëüøèì ïîòåíöèàëîì â îáëàñòè ðåãåíåðàòèâíîé ìåäèöèíû.  ïîñëåäíèå ãîäû â íàó÷íîé ëèòåðàòóðå ïîÿâëÿåòñÿ âñå áîëüøå ïóáëèêàöèé, ïîçâîëÿþùèõ ïðåäñòàâèòü, êàêèì îáðàçîì ïðîèñõîäèò ïîääåðæàíèå èäåíòè÷íîñòè êëåòîê âíóòðåííåé êëåòî÷íîé ìàññû áëàñòîöèñòû (ÂÊÌ) â óñëîâèÿõ in vivo, à òàêæå ïîëó÷àåìûõ èç ÂÊÌ ÝÑÊ in vitro; êàêèå ìîëåêóëÿðíûå ìåõàíèçìû îòâå÷àþò çà êîíòðîëü èõ ñâîéñòâ è îïðåäåëÿþò èõ êîììèòèðîâàíèå è äèôôåðåíöèðîâêó â ñïåöèàëèçèðîâàííûå òèïû êëåòîê. Öåëü íàñòîÿùåãî îáçîðà ñóììèðîâàòü è ïðîàíàëèçèðîâàòü íàêîïèâøèåñÿ ñâåäåíèÿ î ãåíåòè÷åñêèõ è ýïèãåíåòè÷åñêèõ ôàêòîðàõ, ó÷àñòâóþùèõ â ïîääåðæàíèè ñâîéñòâ ýìáðèîíàëüíûõ ñòâîëîâûõ êëåòîê ìëåêîïèòàþùèõ. Self-renewal capacity and pluripotency are the unique features of embryonic stem cells (ESCs), that possess a prominent potential in the field of regenerative medicine. There are growing amount of data describing cell identity within inner cell mass of blastocyst in vivo and within ESCs population in vitro. Molecular mechanisms that are responsible for cells commitment and differentiation into specialized cell types are intensively studied. The aim of this review is to summarize the existing data about genetic and epigenetic mechanisms of mammalian embryonic stem cell self-renewal and pluripotency maintenance. Êëþ÷åâûå ñëîâà: ýìáðèîíàëüíûå ñòâîëîâûå êëåòêè, âíóòðåííÿÿ êëåòî÷íàÿ ìàññà, ñàìîîáíîâëåíèå, ïëþðèïîòåíòíîñòü, Nanog, Oct4, Sox2. Key words: embryonic stem cells, inner cell mass, self-renewal, pluripotency, Nanog, Oct4, Sox2. Ââåäåíèå Ýìáðèîíàëüíûå ñòâîëîâûå êëåòêè (ÝÑÊ), ïîëó÷àåìûå èç êëåòîê âíóòðåííåé êëåòî÷íîé ìàññû áëàñòîöèñòû (ÂÊÌ), õàðàêòåðèçóþòñÿ äâóìÿ îñíîâíûìè ñâîéñòâàìè: ñàìîîáíîâëåíèåì ïîïóëÿöèè è ïëþðèïîòåíòíîñòüþ, òî åñòü ñïîñîáíîñòüþ äèôôåðåíöèðîâàòüñÿ â êëåòêè ïðèìèòèâíîé ýíòîäåðìû, ïðèìèòèâíîé ýêòîäåðìû è òðîôýêòîäåðìû, êîòîðûå çàòåì äàþò íà÷àëî âñåì òèïàì êëåòîê âíåýìáðèîíàëüíûõ è ýìáðèîíàëüíûõ òêàíåé, à òàêæå òêàíåé âçðîñëîãî îðãàíèçìà [1]. Ïî ýòîé ïðè÷èíå îíè îáëàäàþò îãðîìíûì ïîòåíöèàëîì â ñôåðå ðåãåíåðàòèâíîé ìåäèöèíû. Âìåñòå ñ òåì, òðàíñïëàíòàöèè ÝÑÊ â îðãàíèçì æèâîòíûõ ñ ýêñïåðèìåíòàëüíî èíäóöèðîâàííûì èììóíîäåôèöèòîì ïðèâîäÿò ê ôîðìèðîâàíèþ òåðàòîì ïåðâè÷íî äîáðîêà÷åñòâåííûõ îïóõîëåé, âêëþ÷àþùèõ â ñåáÿ ïðîèçâîäíûå òðåõ çàðîäûøåâûõ ëèñòêîâ: ýêòîäåðìû, ìåçîäåðìû è ýíòîäåðìû [2]. Ïîíèìàíèå ìîëåêóëÿðíûõ ìåõàíèçìîâ, îïðåäåëÿþùèõ õàðàêòåðèñòèêè ÝÑÊ, ïîçâîëèëî áû óïðàâëÿòü ïðîöåññàìè ïîääåðæàíèÿ ïëþðèïîòåíòíîñòè è çàïóñêà äèôôåðåíöèðîâêè ýòèõ êëåòîê â îïðåäåëåííûõ íàïðàâëåíèÿõ, èñêëþ÷èâ âåðîÿòíîñòü îáðàçîâàíèÿ îïóõîëåé.  ïîñëåäíèå ãîäû â íàó÷íîé ëèòåðàòóðå ïîÿâëÿåòñÿ âñå áîëüøå ïóáëèêàöèé, ïîçâîëÿþùèõ ñîñòàâèòü ïðåäñòàâëåíèå î òîì, êàêèì îáðàçîì ïðîèñõîäèò ïîääåðæàíèå èäåíòè÷íîñòè êëåòîê âíóòðåííåé êëåòî÷íîé ìàññû áëàñòîöèñòû (ÂÊÌ) â óñëîâèÿõ in vivo äî íà÷àëà êîììèòèðîâàíèÿ è äèôôåðåíöèðîâêè, à òàêæå ÝÑÊ â ïðåäåëàõ ïîïóëÿöèè in vitro [3, 4]. Öåëü îáçîðà ñóììèðîâàòü è ïðîàíàëèçèðîâàòü íàêîïèâøèåñÿ íà ñåãîäíÿøíèé äåíü ñâåäåíèÿ î ãåíåòè÷åñêèõ è ýïèãåíåòè÷åñêèõ ôàêòîðàõ, çàäåéñòâîâàííûõ â ïîääåðæàíèè ñâîéñòâ ýìáðèîíàëüíûõ ñòâîëîâûõ êëåòîê ìëåêîïèòàþùèõ. çàâèñèò, â êàêîé ïîñëåäîâàòåëüíîñòè áóäóò äèôôåðåíöèðîâàòüñÿ ÝÑÊ è êàêèå èç íèõ ñîõðàíÿò ïëþðèïîòåíòíîñòü íà áîëåå äëèòåëüíûé ïåðèîä (ðèñ. 1). Ãîìåîäîìåííûå òðàíñêðèïöèîííûå ôàêòîðû Oct4 (òàêæå íàçûâàåìûé â ëèòåðàòóðå Oct3, ëèáî Pou5f1) è Nanog ñ÷èòàþòñÿ ìíîãèìè àâòîðàìè êëþ÷åâûìè ðåãóëÿòîðàìè ïëþðèïîòåíòíîñòè è ýêñïðåññèðóþòñÿ â ïëþðèïîòåíòíûõ ëèíèÿõ ÝÑÊ in vitro, ÷òî áûëî ïîêàçàíî äëÿ êëåòîê ÷åëîâåêà è ìûøè [5-7] (ðèñ. 2). Ñóùåñòâóåò ãèïîòåçà, ïðåäïîëàãàþùàÿ, ÷òî ñîâìåñòíî ñ ôàêòîðîì FoxD3 îíè ôîðìèðóþò ñèñòåìó ðåãóëÿöèè òðàíñêðèïöèè ñ îòðèöàòåëüíîé îáðàòíîé ñâÿçüþ, ïîääåðæèâàÿ è îãðàíè÷èâàÿ ýêñïðåññèþ äðóã äðóãà [8] (ðèñ. 3). Ïîäàâëåíèå ýêñïðåññèè Oct4 ïðèâîäèò ê ðàííåé äèôôåðåíöèðîâêå ÂÊÌ áëàñòîöèñòû in vivo è ÝÑÊ in vitro â òðîôýêòîäåðìó, â òî âðåìÿ êàê ãèïåðýêñïðåññèÿ ýòîãî ôàêòîðà âûðàæàåòñÿ â äèôôåðåíöèðîâêå ÝÑÊ â ïðèìèòèâíûå ýíòîäåðìó è ìåçîäåðìó. Òàêèì îáðàçîì, äëÿ ïîääåðæàíèÿ ïëþðèïîòåíòíîñòè ýêñïðåññèÿ Oct4 â êëåòêàõ äîëæíà ñòðîãî êîíòðîëèðîâàòüñÿ è ïîääåðæèâàòüñÿ íà îïðåäåëåííîì óðîâíå [9-11]. Oct4 ðåãóëèðóåò ýêñïðåññèþ òêàíåñïåöèôè÷åñêèõ ãåíîâ, âçàèìîäåéñòâóÿ ñ äðóãèìè ôàêòîðàìè, à èìåííî - c FGF-4 (fibroblast growth factor-4), ñïåöèôè÷íûì äëÿ ÝÑÊ [12], Sox2 (high mobility group box protein Sox2) [13]. Ôàêòîð Nanog áûë îïèñàí â 2003 ãîäó èññëåäîâàòåëÿìè èç íàó÷íîé ãðóïïû I. Chambers. [14]. Äî íàñòîÿùåãî âðåìåíè ñ÷èòàëîñü, ÷òî îí íà îïðåäåëåííîì óðîâíå ïîñòîÿííî ýêñïðåññèðóåòñÿ â êëåòêàõ ÂÊÌ è ÝÑÊ , à åãî îòñóòñòâèå ïðèâîäèò ê óòðàòå ïëþðèïîòåíòíîñòè è íåìåäëåííîé äèôôåðåíöèðîâêå ñòâîëîâûõ êëåòîê â ïðèìèòèâíóþ ýíòîäåðìó [14, 15]. Îäíàêî â íàñòîÿùåå âðåìÿ ïîêàçàíî, ÷òî åãî ýêñïðåññèÿ íå êîíñòèòóòèâíà è èçìåíÿåòñÿ â ïðîöåññå ýìáðèîãåíåçà, ìîäóëèðóÿ ñïîñîáíîñòü ÝÑÊ ê îáðàçîâàíèþ ñïåöèàëèçèðîâàííûõ òèïîâ êëåòîê; à ïðè èñêóññòâåííîì áëîêèðîâàíèè ýêñïðåññèè Nanog â ÝÑÊ íå ïðîèñõîäèò íåìåäëåííîé àêòèâàöèè ïðîöåññîâ äèôôåðåíöèðîâêè è êëåòêè ñîõðàíÿþò ïëþðèïîòåíòíîñòü, ïîëíîñòüþ óòðà÷èâàÿ, îäíàêî, ñïîñîáíîñòü äàâàòü íà÷àëî ëèíèè ïåðâè÷íûõ ïîëîâûõ êëåòîê [16-18]. Ãåíåòè÷åñêèé êîíòðîëü ïëþðèïîòåíòíîñòè: ôàêòîðû Oct4, Nanog è Sox2  ïðîöåññå ýìáðèîíàëüíîãî ðàçâèòèÿ ïðîèñõîäèò ïîñòåïåííîå èçìåíåíèå ñïåêòðà òðàíñêðèïöèîííûõ ôàêòîðîâ, äåéñòâóþùèõ â ðàçëè÷íûõ êëåòî÷íûõ ïîïóëÿöèÿõ. Îò ýòîãî Êëåòî÷íàÿ òðàíñïëàíòîëîãèÿ è òêàíåâàÿ èíæåíåðèÿ Òîì III, ¹ 2, 2008 Îáçîðû 39 Ðèñ. 1. Èçìåíåíèå ýêñïðåññèè òðàíñêðèïöèîííûõ ôàêòîðîâ â ïðîöåññå ýìáðèîíàëüíîãî ðàçâèòèÿ. Oct4, Nanog è Sox2 ýêñïðåññèðóþòñÿ â ëèíèÿõ ïëþðèïîòåíòíûõ êëåòîê. Ïîêàçàíû ôàêòîðû, îòâåòñòâåííûå çà ðàçâèòèå òðîôýêòîäåðìû (Ñdx2), ýêñòðàýìáðèîíàëüíîé ýíòîäåðìû (Gata6) è ñîìàòè÷åñêèõ êëåòî÷íûõ ëèíèé (GCNF) [ïî Johnson B.V. et al., 2006 ñ èçì.] Ðèñ. 2. Èçìåíåíèå ñîîòíîøåíèÿ êîíöåíòðàöèé Oct4 è Nanog â ïëþðèïîòåíòíûõ ÝÑÊ ìûøè ïðèâîäèò ê ïîòåðå èëè ìîäèôèêàöèÿì èõ ñâîéñòâ. Ïðè ðàâíûõ âíóòðèêëåòî÷íûõ êîíöåíòðàöèÿõ ýòèõ ôàêòîðîâ è ýêçîãåííîé ñòèìóëÿöèè LIF ÝÑÊ ñïîñîáíû ê ñàìîîáíîâëåíèþ. Äåëåöèÿ Nanog ïðèâîäèò ê äèôôåðåíöèðîâêå ÝÑÊ â ïðèìèòèâíóþ ýíòîäåðìó, äåëåöèÿ Oct4 ê äèôôåðåíöèðîâêå â òðîôýêòîäåðìó. Ïîâûøåíèå êîíöåíòðàöèè Oct4 íà 50% âûçûâàåò îáðàçîâàíèå èç ÝÑÊ ñìåøàííîé ïîïóëÿöèè, â êîòîðîé ïðèñóòñòâóþò êëåòêè ýíòîäåðìàëüíîãî è ìåçîäåðìàëüíîãî ïðîèñõîæäåíèé. Äî íàñòîÿùåãî âðåìåíè íå èçâåñòåí ôåíîòèï ÝÑÊ, â êîòîðûõ îäíîâðåìåííî ïîâûøåíû óðîâíè Oct4 è Nanog [ïî Chambers I. et al., 2004 ñ èçì.] Êëåòî÷íàÿ òðàíñïëàíòîëîãèÿ è òêàíåâàÿ èíæåíåðèÿ Òîì III, ¹ 2, 2008 40 Îáçîðû Ðèñ. 3. Ñõåìà âçàèìîäåéñòâèÿ ôàêòîðîâ ñàìîîáíîâëåíèÿ. À. Oct4 è Nanog íåîáõîäèìû äëÿ ïîääåðæàíèÿ ñàìîîáíîâëåíèÿ ÝÑÊ. Ïðåäïîëàãàåìàÿ ìîäåëü ðåãóëÿòîðíîé ñèñòåìû, âêëþ÷àþùåé Oct4, Nanog è FoxD3. FoxD3 è Nanog ÿâëÿþòñÿ ïîçèòèâíûìè ðåãóëÿòîðàìè òðàíñêðèïöèè Oct4, â òî âðåìÿ êàê Oct4 ïîäàâëÿåò ñîáñòâåííóþ ýêñïðåññèþ è ýêñïðåññèþ Nanog. Á. Ñõåìàòè÷åñêàÿ äèàãðàììà âçàèìîäåéñòâèÿ Oct4, Nanog è FoxD3 [ïî Pan G. et al., 2006 ñ èçì.] ïîäàâëåíèþ òðàíñêðèïöèè Nanog, ÿâëÿåòñÿ Laminin-b1 [25]. Èç ýòîãî ìîæíî çàêëþ÷èòü, ÷òî íåêîòîðûå ôàêòîðû, ôóíêöèè êîòîðûõ ñ÷èòàþòñÿ õîðîøî èçâåñòíûìè è íå ñâÿçàííûìè ñ ïîääåðæàíèåì ñâîéñòâ ýìáðèîíàëüíûõ ñòâîëîâûõ êëåòîê, ìîãóò òàêæå ó÷àñòâîâàòü â ïîääåðæàíèè ïëþðèïîòåíòíîñòè è ñàìîîáíîâëåíèÿ. Oct4, Sox2 è Nanog ñ÷èòàþòñÿ ôàêòîðàìè, îòâåòñòâåííûìè êàê çà ïëþðèïîòåíòíîñòü, òàê è çà âûáîð ïóòè äèôôåðåíöèðîâêè ÝÑÊ. Îíè îïðåäåëÿþò ýêñïðåññèîííûå ïàòòåðíû òðàíñêðèïöèîííûõ ôàêòîðîâ, ýêñïðåññèðóþùèõñÿ â êëåòêàõ ÂÊÌ ïî ïðîõîæäåíèè ýìáðèîíîì ñòàäèè áëàñòîöèñòû è â ÝÑÊ ïðè èõ êîììèòèðîâàíèè ê äèôôåðåíöèðîâêå. Ñîâðåìåííûå äàííûå ïîçâîëÿþò ñîñòàâèòü äîâîëüíî ïîäðîáíóþ ñõåìó êîíòðîëÿ ïëþðèïîòåíòíîñòè. Êàðòèðîâàíèå ñàéòîâ ñâÿçûâàíèÿ Oct4 è Nanog â ÄÍÊ ýìáðèîíàëüíûõ ñòâîëîâûõ êëåòîê ÷åëîâåêà è ìûøè [7, 25] ïîçâîëèëî âûÿâèòü ðÿä ãåíîâ, ñ êîòîðûìè âçàèìîäåéñòâóþò Oct4, Nanog è Sox2, à òàêæå îöåíèòü ñòåïåíü âëèÿíèÿ êàæäîãî èç ýòèõ ôàêòîðîâ íà ïðîöåññû ðàçâèòèÿ, ïîñòðîèâ, òàêèì îáðàçîì, èåðàðõèþ òðàíñêðèïöèîííûõ ôàêòîðîâ, äåéñòâóþùèõ â ÝÑÊ (ðèñ. 4). Îäíàêî òàêàÿ èåðàðõèÿ, êàê ïîêàçûâàþò ìíîãèå ðàáîòû, íå óíèâåðñàëüíà, è î íåé ìîæíî ãîâîðèòü òîëüêî ïðèìåíèòåëüíî ê êàæäîìó îòäåëüíîìó âèäó æèâûõ îðãàíèçìîâ [26], ÷òî âûíóæäàåò ê îñòîðîæíîé èíòåðïðåòàöèè äàííûõ, ïîëó÷åííûõ íà ìîäåëüíûõ îáúåêòàõ, ïðè îáúÿñíåíèè ïðîöåññîâ, ïðîèñõîäÿùèõ â ÝÑÊ ÷åëîâåêà. Òàêèì îáðàçîì, ñóùåñòâóåò îãðàíè÷åííûé íàáîð êëþ÷åâûõ òðàíñêðèïöèîííûõ ôàêòîðîâ, õàðàêòåð ýêñïðåññèè êîòîðûõ ñóùåñòâåíåí äëÿ ðàííèõ ýòàïîâ ðàçâèòèÿ ýìáðèîíà è äèôôåðåíöèðîâêè ÝÑÊ â êóëüòóðå.  òî æå âðåìÿ ýôôåêòû ýòèõ áåëêîâ íåîäèíàêîâû â óñëîâèÿõ in vivo è in vitro, òàê êàê, ïî-âèäèìîìó, ñóùåñòâóþò äî íàñòîÿùåãî âðåìåíè íåèçâåñòíûå ìåõàíèçìû, èãðàþùèå âàæíóþ ðîëü â çàïóñêå òåõ èëè èíûõ ñèãíàëüíûõ ïóòåé â êëåòêàõ. Ñàìàÿ ïðîñòàÿ ìîäåëü ðàáîòû áåëêîâ Oct4, Nanog è Sox2 ïðåäïîëàãàåò, ÷òî ýòè ôàêòîðû ñîâìåñòíî îïðåäåëÿþò äàëüíåéøåå ðàçâèòèå ÝÑÊ, âçàèìîäåéñòâóÿ ñ äðóãèìè òðàíñêðèïöèîííûìè ôàêòîðàìè, îòâåòñòâåííûìè çà äèôôåðåíöèðîâêó (òàáë.). Òàê, íàïðèìåð, áûëî ïðîäåìîíñòðèðîâàíî, ÷òî áàëàíñ Oct4 è ãîìåîäîìåííîãî áåëêà Cdx2 âëèÿåò íà äèôôåðåíöèðîâêó ÝÑÊ â êëåòêè òðîôýêòîäåðìû [19]. Oct4 è Cdx2 ÿâëÿþòñÿ àíòàãîíèñòàìè, ïîäàâëÿÿ ýêñïðåññèþ äðóã äðóãà. Oct4 îòâåòñòâåíåí çà îáðàçîâàíèå ÂÊÌ, èç êîòîðîé ïîëó÷àþò ÝÑÊ, â òî âðåìÿ êàê Cdx2 íåîáõîäèì äëÿ ðàçâèòèÿ òðîôýêòîäåðìû [20]. Oct4 è Cdx2 òàêæå ðåãóëèðóþò ðàáîòó áåëêà ýîìåçîäåðìèíà (eomesodermin), êîòîðûé íåîáõîäèì äëÿ ðàçâèòèÿ òðîôýêòîäåðìû [10]. Èç ýòîãî ìîæíî çàêëþ÷èòü, ÷òî äëÿ ïåðâè÷íîé ñåãðåãàöèè ÂÊÌ è òðîôýêòîäåðìû òðåáóåòñÿ ñî÷åòàííîå äåéñòâèå ïî êðàéíåé ìåðå òðåõ òðàíñêðèïöèîííûõ ôàêòîðîâ. Ïîõîæèì îáðàçîì áàëàíñ óðîâíåé ôàêòîðà Nanog è ïðîäóêòîâ öåëîãî ðÿäà ãåíîâ: Cdx2, Gata2, hCG-α è hCG-β îïðåäåëÿåò äèôôåðåíöèðîâêó ÝÑÊ â òðîôýêòîäåðìó [21], à ñîîòíîøåíèå êîíöåíòðàöèé Nanog, Gata4 è Gata6 ðåãóëèðóåò äèôôåðåíöèðîâêó ÝÑÊ â ýíòîäåðìàëüíîì íàïðàâëåíèè. Ïîâûøåíèå ýêñïðåññèè Gata4 è Gata6 â êëåòêàõ ÂÊÌ âåäåò ê èõ äèôôåðåíöèðîâêå â ýíòîäåðìàëüíîì íàïðàâëåíèè, ÷òî ïðîèñõîäèò è ïðè ïîäàâëåíèè ýêñïðåññèè Nanog, êîòîðûé, â ÷àñòíîñòè, ÿâëÿåòñÿ íåãàòèâíûì òðàíñêðèïöèîííûì ðåãóëÿòîðîì ýêñïðåññèè Gata4 è Gata6 [15, 17, 21, 22-24]. Ñëåäóåò îòìåòèòü, ÷òî Gata4 è Gata6 íå ÿâëÿþòñÿ åäèíñòâåííûìè àíòàãîíèñòàìè Nanog, îïðåäåëÿþùèìè äèôôåðåíöèðîâêó â ýíòîäåðìàëüíîì íàïðàâëåíèè. Îäíèì èç ìåíåå óïîìèíàåìûõ ãåíîâ, ýêñïðåññèÿ êîòîðîãî â ÝÑÊ ÷åëîâåêà ïðèâîäèò ê Ýïèãåíåòè÷åñêèé êîíòðîëü ïëþðèïîòåíòíîñòè  äàííîì ñëó÷àå ïîä «ýïèãåíåòè÷åñêèìè» ðàññìàòðèâàþòñÿ âíóòðèêëåòî÷íûå ôàêòîðû ðåîðãàíèçàöèè õðîìàòèíà, îêàçûâàþùèå âëèÿíèå íà ýêñïðåññèþ ãåíîìà. Ðåîðãàíèçàöèÿ õðîìàòèíà ÿâëÿåòñÿ íåîòúåìëåìîé ÷àñòüþ àêòèâàöèè ãåíåòè÷åñêèõ ïðîãðàìì, ðåàëèçàöèÿ êîòîðûõ îïðåäåëÿåò íàïðàâëåíèå äèôôåðåíöèðîâêè ñòâîëîâûõ êëåòîê êàê in vivo, òàê è in vitro [26-28]. Íàïðèìåð, õðîìàòèí â ÝÑÊ ïðåäñòàâëåí â îñíîâíîì òðàíñêðèïöèîííî àêòèâíûì ýóõðîìàòèíîì, ÷òî ïîäòâåðæäàåòñÿ íàëè÷èåì áîëüøîãî êîëè÷åñòâà àöåòèëèðîâàííûõ ãèñòîíîâ è ïîâûøåííîé ÷óâñòâèòåëüíîñòüþ õðîìàòèíà ê íóêëåàçàì.  òî æå âðåìÿ êîììèòèðîâàíèå êëåòîê ñîïðîâîæäàåòñÿ ïîíèæåíèåì ñòåïåíè àöåòèëèðîâàíèÿ ãèñòîíîâ è ñîïóòñòâóþùèì óâåëè÷åíèåì ïðîöåíòà íåàêòèâíîãî ãåòåðîõðîìàòèíà. Òàêèì îáðàçîì, îãðàíè÷åíèå ïëþðèïîòåíòíîñòè òåñíî ñâÿçàíî ñ óìåíüøåíèåì ïëàñòè÷íîñòè ãåíîìà ÝÑÊ [28]. Àíàëèç èçìåíåíèé îðãàíèçàöèè õðîìàòèíà â ÝÑÊ äåìîíñòðèðóåò âûñîêóþ ñòåïåíü äèíàìè÷åñêîé àññîöèàöèè ñòðóêòóðíûõ ïðîòåèíîâ (îñíîâíûõ è âàðèàáåëüíûõ ãèñòîíîâ, ëèíêåðíîãî ãèñòîíà H1, ãèñòîíà H3, à òàêæå ïðîòåèíà, àññîöèèðîâàííîãî ñ ãåòåðîõðîìàòèíîì HP1α) ñ õðîìàòèíîì ïëþðèïîòåíòíûõ ÝÑÊ â îòëè÷èå îò õðîìàòèíà äèôôåðåíöèðîâàííûõ êëåòîê. Çàìåíà ãèñòîíà H1 åãî ìîäèôèêàöèåé, èìåþùåé áîëåå âûñîêîå ñðîäñòâî ê ÄÍÊ, ïðèâîäèò ê èíãèáèðîâàíèþ äèôôåðåíöèðîâêè ÝÑÊ; â òî âðåìÿ êàê çàìåíà ãèñòîíà H3 åãî ìîäèôèêàöèåé H3.3, ÿâëÿþùåéñÿ ìàðêåðîì àêòèâíîé òðàíñêðèïöèè, óñêîðÿåò äèôôåðåíöèðîâêó ÝÑÊ [29]. Èç ýòîãî ìîæíî ñäåëàòü âûâîä, ÷òî ñòðóêòóðíûå áåëêè õðîìàòèíà â ÝÑÊ ñëàáî ñâÿçàíû ñ ÄÍÊ, îáåñïå÷èâàÿ áûñòðóþ ðåîðãàíèçàöèþ õðîìàòèíà â ïðîöåññå äèôôåðåíöèðîâêè. Êëåòî÷íàÿ òðàíñïëàíòîëîãèÿ è òêàíåâàÿ èíæåíåðèÿ Òîì III, ¹ 2, 2008 41 Îáçîðû Òàáëèöà. Òðàíñêðèïöèîííûå ôàêòîðû, îïðåäåëÿþùèå ïëþðèïîòåíòíîñòü ÝÑÊ è èõ äèôôåðåíöèðîâêó [ïî äàííûì Boyer L.A. et al., 2006; Kehler J. et al., 2004; Maruyama M. et al., 2005; Shi W. et al., 2006; Suzuki A. et al., 2006] Òðàíñêðèïöèîííûé ôàêòîð Ðåçóëüòàò ïîäàâëåíèÿ ýêñïðåññèè Ïàòòåðí ýêñïðåññèè â ýìáðèîíàëüíîì ðàçâèòèè â ÝÑÊ Ôóíêöèÿ Oct4 Ýêñïðåññèðóåòñÿ â îâîöèòå, â îïëîäîòâîðåííîé ÿéöåêëåòêå, êëåòêàõ ÂÊÌ, ýïèáëàñòå, ÝÑÊ, êëåòêàõ ýìáðèîíàëüíîé êàðöèíîìû è ëèíèè ïåðâè÷íûõ ïîëîâûõ êëåòîê Ãèáåëü ýìáðèîíîâ íà ñòàäèè áëàñòîöèñòû, äèôôåðåíöèðîâêà êëåòîê ýïèáëàñòà â òðîôýêòîäåðìó, àïîïòîç ïåðâè÷íûõ ïîëîâûõ êëåòîê Ïîòåðÿ ïëþðèïîòåíòíîñòè, äèôôåðåíöèðîâêà â òðîôýêòîäåðìó Äèôôåðåíöèðîâêà â ýíòîäåðìàëüíîì è ìåçîäåðìàëüíîì íàïðàâëåíèÿõ Nanog Ýêñïðåññèðóåòñÿ â êëåòêàõ ìîðóëû, ÂÊÌ, ýïèáëàñòà, ÝÑÊ, ýìáðèîíàëüíîé êàðöèíîìû è ëèíèè ïåðâè÷íûõ ïîëîâûõ êëåòîê Ãèáåëü ýìáðèîíîâ, íåäîðàçâèòèå ýïèáëàñòà, äèôôåðåíöèðîâêà ÂÊÌ â òðîôýêòîäåðìó, áëîê ðàçâèòèÿ ëèíèè ïåðâè÷íûõ ïîëîâûõ êëåòîê Ïîòåðÿ ïëþðèïîòåíòíîñòè, äèôôåðåíöèðîâêà â ïðèìèòèâíóþ ýíòîäåðìó LIF-íåçàâèñèìîå ñàìîîáíîâëåíèå ïîïóëÿöèé ÝÑÊ, óñòîé÷èâîñòü ê èíäóêöèè äèôôåðåíöèðîâêè ðåòèíîåâîé êèñëîòîé, áëîêèðîâàíèå äèôôåðåíöèðîâêè ÝÑÊ â ìåçîäåðìàëüíîì íàïðàâëåíèè, èíäóöèðîâàííîé ôàêòîðîì BMP Sox2 Ýêñïðåññèðóåòñÿ â îâîöèòå, ÂÊÌ, ýïèáëàñòå, ëèíèè ïåðâè÷íûõ ïîëîâûõ êëåòîê, ìóëüòèïîòåíòíûõ êëåòêàõ âíåçàðîäûøåâîé ýêòîäåðìû, êëåòêàõ-ïðåäøåñòâåííèöàõ íåðâíîé òêàíè, ýíòîäåðìå Ãèáåëü ýìáðèîíîâ â ñâÿçè ñ íåñïîñîáíîñòüþ îáðàçîâûâàòü ýïèáëàñò Íàðóøåíèå ýêñïðåññèè ãåíîâ Fgf4 è Fbx15 Sox15 Ýêñïðåññèðóåòñÿ â îâîöèòå, ÂÊÌ, ýïèáëàñòå, ëèíèè ïåðâè÷íûõ ïîëîâûõ êëåòîê, ìóëüòèïîòåíòíûõ êëåòêàõ âíåçàðîäûøåâîé ýêòîäåðìû, êëåòêàõ-ïðåäøåñòâåííèöàõ íåðâíîé òêàíè, ýíòîäåðìå Ýìáðèîíû ðàçâèâàþòñÿ íîðìàëüíî Íàðóøåíèå ýêñïðåññèè ôàêòîðîâ Otx2, Ctgf, Ebaf, Hrc Stat3 Ýêñïðåññèðóåòñÿ áîëüøèíñòâîì òèïîâ êëåòîê êàê íåäèôôåðåíöèðîâàííûõ, òàê è äèôôåðåíöèðîâàííûõ Ãèáåëü ýìáðèîíîâ íà ñòàäèè áëàñòîöèñòû Äèôôåðåíöèðîâêà â ïðèìèòèâíóþ ýêòîäåðìó è ìåçîäåðìó (ïîêàçàíî äëÿ ÝÑÊ ìûøè) LIF-íåçàâèñèìîå ñàìîîáíîâëåíèå ïîïóëÿöèé ÝÑÊ Cdx2 Ýêñïðåññèðóåòñÿ â íàðóæíûõ êëåòêàõ ìîðóëû, à òàêæå êëåòêàõ òðîôýêòîäåðìû Ãèáåëü ýìáðèîíîâ íà ñòàäèè èìïëàíòàöèè Îñòàíîâêà äèôôåðåíöèðîâêè â òðîôýêòîäåðìó Äèôôåðåíöèðîâêà ÝÑÊ â êëåòêè òðîôîáëàñòà Gata6 Ýêñïðåññèðóåòñÿ â êëåòêàõ âíåçàðîäûøåâîé ýíòîäåðìû Ãèáåëü ýìáðèîíîâ â ñâÿçè ñ äåôåêòàìè ôîðìèðîâàíèÿ âèñöåðàëüíîé ýíòîäåðìû Äèôôåðåíöèðîâêà ÝÑÊ â ýíòîäåðìàëüíîì íàïðàâëåíèè Gata4 Ýêñïðåññèðóåòñÿ â êëåòêàõ âíåçàðîäûøåâîé ýíòîäåðìû Ãèáåëü ýìáðèîíîâ â ñâÿçè ñ äåôåêòàìè ìîðôîãåíåçà ñåðäöà Íåñïîñîáíîñòü ÝÑÊ äèôôåðåíöèðîâàòüñÿ â êëåòêè âèñöåðàëüíîé ýíòîäåðìû Äèôôåðåíöèðîâêà ÝÑÊ â ýíòîäåðìàëüíîì íàïðàâëåíèè Rex-1 Ýêñïðåññèðóåòñÿ èñêëþ÷èòåëüíî â êëåòêàõ ÂÊÌ è â òåðàòîêàðöèíîìàõ, îáðàçóþùèõñÿ èç ÝÑÊ Êëåòî÷íàÿ òðàíñïëàíòîëîãèÿ è òêàíåâàÿ èíæåíåðèÿ Òîì III, ¹ 2, 2008 42 Îáçîðû Ðèñ. 4. Èåðàðõèÿ òðàíñêðèïöèîííûõ ôàêòîðîâ, îòâå÷àþùèõ çà ïëþðèïîòåíòíîñòü è äèôôåðåíöèðîâêó ÝÑÊ ìûøè è ÷åëîâåêà [ïî Boyer L.A., 2006 ñ èçì.] Êëåòî÷íàÿ òðàíñïëàíòîëîãèÿ è òêàíåâàÿ èíæåíåðèÿ Òîì III, ¹ 2, 2008 Îáçîðû Ñ ýòèì ñîãëàñóåòñÿ òîò ôàêò, ÷òî òêàíåñïåöèôè÷íûå ãåíû â ãåíîìå ÝÑÊ íàõîäÿòñÿ â ñîñòîÿíèè ïîäàâëåííîé àêòèâíîñòè. Èõ àêòèâàöèÿ ïðè êîììèòèðîâàíèè ÝÑÊ ïðîèñõîäèò î÷åíü áûñòðî, òàê êàê â ÝÑÊ ïîñòîÿííî ïðèñóòñòâóþò àêòèâíûå ýïèãåíåòè÷åñêèå ðåãóëÿòîðû [30, 31]. Ó÷àñòêè ÄÍÊ â ÿäðàõ ÝÑÊ, ñîäåðæàùèå ìíîãèå òêàíåñïåöèôè÷íûå ãåíû, îáðàçóþò êîìïëåêñû ñ òàê íàçûâàåìûìè áèâàëåíòíûìè ñòðóêòóðíûìè ïðîòåèíàìè, ñîñòîÿùèìè èç ñóïðåññîðíîãî ãèñòîíà H3K27me3 è àêòèâèðóþùåãî ãèñòîíà H3K4me3. Ýòî ïðèâîäèò ê áûñòðîìó ïåðåêëþ÷åíèþ òðàíñêðèïöèîííûõ êàñêàäîâ â ïðîöåññå ýìáðèîíàëüíîãî ðàçâèòèÿ [32, 33]. Ñëåäóåò îòìåòèòü, ÷òî áîëüøèíñòâî ãåíîâ-ìèøåíåé Oct4, Sox2 è Nanog íàõîäÿòñÿ â ñîñòàâå òàêèõ áèâàëåíòíûõ äîìåíîâ â ÄÍÊ, ÷òî îáåñïå÷èâàåò èõ áûñòðóþ ðåãóëÿöèþ (àêòèâàöèþ è ñóïðåññèþ) êàê â ïðîöåññå ðàçâèòèÿ áëàñòîöèñòû in vivo, òàê è ïðè êóëüòèâèðîâàíèè ÝÑÊ in vitro [25, 33-34]. Òàêæå ñëåäóåò ïðèíèìàòü âî âíèìàíèå ó÷àñòèå â ðåãóëÿöèè èõ ýêñïðåññèè õðîìàòèí-ðåìîäóëèðóþùèõ òðàíñêðèïöèîííûõ ðåïðåññîðîâ èç ñåìåéñòâà Polycomb-áåëêîâ (PcG), êîòîðûå ìîãóò èíäóöèðîâàòü êàê ëîêàëüíûå, òàê è ãëîáàëüíûå ïåðåñòðîéêè ñòðóêòóðû õðîìàòèíà, òåì ñàìûì âëèÿÿ íà ýêñïðåññèþ ãåíîìà. Ðîëü PcG-ôàêòîðîâ â ïîääåðæàíèè ñâîéñòâ ÝÑÊ PcG-ãåíû âêëþ÷àþò ïî êðàéíåé ìåðå äâà ðàçëè÷íûõ ðåïðåññîðíûõ êîìïëåêñà (PRC1 è PRC2-PRC3), ñòðîåíèå êîòîðûõ êðàéíå êîíñåðâàòèâíî [37]. Ðîëü èõ â ïîääåðæàíèè ïëþðèïîòåíòíîñòè ñâÿçàíà ñ ó÷àñòèåì â ôîðìèðîâàíèè ïàòòåðíà ýêñïðåññèè ãåíîâ, îòâå÷àþùèõ çà ïåðâûå ýòàïû ðàçâèòèÿ ýìáðèîíà in vivo [38-45], ôîðìèðîâàíèå ïëþðèïîòåíòíûõ ëèíèé ÝÑÊ â êóëüòóðàõ in vitro [40] è ïîääåðæàíèå íåäèôôåðåíöèðîâàííîãî ñîñòîÿíèÿ ñòâîëîâûõ êëåòîê âçðîñëîãî îðãàíèçìà [42, 43]. Èññëåäîâàíèÿ, ïðîâåäåííûå íà ÝÑÊ ÷åëîâåêà è ìûøè, ïîêàçàëè, ÷òî PRC1 è PRC2 ñâÿçûâàþòñÿ ñ øèðîêèì ñïåêòðîì ãåíîâ, ïðåäñòàâëÿþùèõ ñîáîé òðàíñêðèïöèîííûå è ñèãíàëüíûå ôàêòîðû, ðîëü êîòîðûõ â ðàçâèòèè èçâåñòíà. Ãåíû, ñâÿçàííûå ñ PcG-ïðîòåèíàìè, â ñâîåé ïðîìîòîðíîé îáëàñòè òàêæå ñîäåðæàò ãèñòîí H3K27me3, ÷üÿ ñóïðåññèâíàÿ àêòèâíîñòü êàòàëèçèðóåòñÿ PRC2. Òàêèì îáðàçîì, PcGôàêòîðû ÿâëÿþòñÿ ñóïðåññîðàìè òðàíñêðèïöèîííîé àêòèâíîñòè òêàíåñïåöèôè÷åñêèõ ãåíîâ â ÝÑÊ [33, 35].  îòñóòñòâèè îäíîãî èç êîìïîíåíòîâ PRC2 ñóáúåäèíèöû Eed - ÝÑÊ ïðåòåðïåâàþò ñïîíòàííóþ ðàçíîíàïðàâëåííóþ äèôôåðåíöèðîâêó [35], ïðè ýòîì îòñóòñòâèå äðóãîãî êîìïîíåíòà Ezn2 íèêàê íå âëèÿåò íà ñàìîîáíîâëåíèå è ñîõðàíåíèå ïëþðèïîòåíòíîñòè ïîïóëÿöèé ÝÑÊ [40]. Ýòî ãîâîðèò î Eed êàê îá îäíîì èç êëþ÷åâûõ áåëêîâ â ðåãóëÿöèè ïîääåðæàíèÿ ïëþðèïîòåíòíîñòè ÝÑÊ. Òåì íå ìåíåå, ôàêòîðó PRC2 è áåëêó Eed â ëèòåðàòóðå óäåëÿåòñÿ ìàëî âíèìàíèÿ. Òàêèì îáðàçîì, ñëîæíî ãîâîðèòü î ðîëè âñåõ PcG-ïðîòåèíîâ â ïîääåðæàíèè ïëþðèïîòåíòíîñòè ÝÑÊ. Áîëüøîå ÷èñëî PcG-ïðîòåèíîâ àññîöèèðîâàíî ñ ãåíàìè Oct4, Sox2 è Nanog, îäíàêî íå ñëóæèò äëÿ ïîäàâëåíèÿ èõ ýêñïðåññèè. Ïîâèäèìîìó, Oct4, Sox2 è Nanog ìîãóò ñëóæèòü ñèãíàëàìè äëÿ àêòèâàöèè PcG-ïðîòåèíîâ è ïîñëåäóþùåé ñóïðåññèè òêàíåñïåöèôè÷íûõ ãåíîâ [34, 35], íî ñ óâåðåííîñòüþ äåëàòü ïîäîáíûé âûâîä ïðåæäåâðåìåííî. Ðîëü ìåòèëèðîâàíèÿ ãèñòîíîâ è ÄÍÊ â ïîääåðæàíèè ñâîéñòâ ÝÑÊ Ñâèäåòåëüñòâà âëèÿíèÿ óðîâíÿ ìåòèëèðîâàíèÿ ãèñòîíîâ è ÄÍÊ íà ýêñïðåññèþ ãåíîìà ìîæíî îáíàðóæèòü â íåñêîëüêèõ ýêñïåðèìåíòàëüíûõ ðàáîòàõ, ãäå áûëè ïîêàçàíû äèíàìè÷åñêèå èçìåíåíèÿ ìåòèëèðîâàíèÿ ãèñòîíîâ [46] è ÄÍÊ [47] in vivo íà ðàçâèâàþùèõñÿ ýìáðèîíàõ ìûøè. Ñðàçó ïîñëå îïëîäîòâîðåíèÿ â ÿéöåêëåòêå òàêèõ ìëåêîïèòàþùèõ, êàê 43 ìûøü è ÷åëîâåê, ïàäàåò óðîâåíü ìåòèëèðîâàíèÿ ÄÍÊ [48], âîññòàíàâëèâàÿñü ê ñòàäèè áëàñòîöèñòû â êëåòêàõ ÂÊÌ [47] è âíîâü ïîñòåïåííî ñíèæàÿñü ïî ìåðå ðàçâèòèÿ ýìáðèîíà [49]. Ïðîôèëü ìåòèëèðîâàíèÿ ïðè ýòîì ñòðîãî âèäîñïåöèôè÷åí, è ó äðóãèõ âèäîâ ìëåêîïèòàþùèõ, òàêèõ êàê êîðîâà, îâöà è ñâèíüÿ, âîññòàíîâëåíèÿ ìåòèëèðîâàíèÿ íà ñòàäèè áëàñòîöèñòû íå ïðîèñõîäèò [50]. Ïî-âèäèìîìó, ìåòèëèðîâàíèå áîëåå ïîçäíåå ýâîëþöèîííîå ïðèîáðåòåíèå, ÷åì PcG-ôàêòîðû, è íå ÿâëÿåòñÿ óíèâåðñàëüíûì ìåõàíèçìîì ðåïðåññèè òðàíñêðèïöèè è ïîäàâëåíèÿ äèôôåðåíöèðîâêè êëåòîê [51]. Íàèáîëåå ðàñïðîñòðàíåííîé ðàçíîâèäíîñòüþ ýïèãåíåòè÷åñêèõ èçìåíåíèé â êëåòêàõ ìëåêîïèòàþùèõ ÿâëÿåòñÿ ñèììåòðè÷íîå ìåòèëèðîâàíèå öèòîçèíà â 5’ ïîçèöèè â CpG äèíóêëåîòèäàõ (â êîòîðûõ çà öèòîçèíîì ðàñïîëàãàåòñÿ ãóàíèí) [52]. Ëîêóñ-ñïåöèôè÷åñêîå ìåòèëèðîâàíèå ãèñòîíîâ è ÄÍÊ â êëåòêàõ âíóòðåííåé êëåòî÷íîé ìàññû ñîõðàíÿåòñÿ â ïîëó÷àåìûõ èç íèõ êóëüòóðàõ ÝÑÊ [50].  ñëó÷àå ïðèñóòñòâèÿ â êëåòêàõ ÂÊÌ ýïèãåíåòè÷åñêèõ íàðóøåíèé, ýòè íàðóøåíèÿ ñîõðàíÿþòñÿ â ÝÑÊ è èõ ïðîèçâîäíûõ [53]. Ýïèãåíåòè÷åñêèå èçìåíåíèÿ â ÝÑÊ ÷åëîâåêà èìåþò áîëüøîå çíà÷åíèå ñ òî÷êè çðåíèÿ ïðèìåíåíèÿ ýòèõ êëåòîê â öåëÿõ ðåãåíåðàòèâíîé ìåäèöèíû. Óðîâåíü ìåòèëèðîâàíèÿ ÄÍÊ ìîæåò îãðàíè÷èâàòü èëè, íàïðîòèâ, ñòèìóëèðîâàòü äèôôåðåíöèðîâêó ÝÑÊ â îïðåäåëåííûå òèïû êëåòîê [5456]. Íàïðèìåð, äèôôåðåíöèðîâêà ÝÑÊ â êàðäèîìèîöèòû ìîæåò áûòü óñêîðåíà ñ ïîìîùüþ ïðèìåíåíèÿ èíãèáèòîðîâ ôåðìåíòà ÄÍÊ-ìåòèëòðàíñôåðàçû [57]. Îòíîñèòåëüíî ñïîñîáíîñòè ÝÑÊ ïðèâîäèòü ê ôîðìèðîâàíèþ òåðàòîì ïðè òðàíñïëàíòàöèè â îðãàíèçì æèâîòíûõ ñ ýêñïåðèìåíòàëüíî èíäóöèðîâàííûì èììóíîäåôèöèòîì òàêæå ñóùåñòâóåò òî÷êà çðåíèÿ, ÷òî îïóõîëè îáðàçóþòñÿ èç êëåòîê ñ íàðóøåíèÿìè ìåòèëèðîâàíèÿ ãåíîìà [50], ïîñêîëüêó ìíîãèå òèïû îíêîëîãè÷åñêèõ çàáîëåâàíèé ÷åëîâåêà ñâÿçàíû ñ ãèïåðìåòèëèðîâàíèåì èëè, íàîáîðîò, ãèïîìåòèëèðîâàíèåì îïðåäåëåííûõ ó÷àñòêîâ ÄÍÊ [58]. Ñ ïîìîùüþ ìåòèëèðîâàíèÿ ìîãóò áûòü ïîäàâëåíû ãåíûñóïðåññîðû îïóõîëåâîãî ðîñòà èëè, íàïðîòèâ, àêòèâèðîâàíû ïðîòîîíêîãåíû. Ïîìèìî çíà÷èìîñòè äëÿ ìåäèöèíû, õàðàêòåðèñòèêà èçìåíåíèÿ ïðîôèëÿ ìåòèëèðîâàíèÿ â êëåòêàõ ÂÊÌ ïðè ðàçâèòèè áëàñòîöèñòû è ÝÑÊ â ïðîöåññå êóëüòèâèðîâàíèÿ in vitro è äèôôåðåíöèðîâêè, à òàêæå ðàçëè÷èÿ ïðîôèëåé ìåòèëèðîâàíèÿ ìåæäó ðàçíûìè êëåòî÷íûìè ëèíèÿìè ÝÑÊ ÿâëÿåòñÿ ôóíäàìåíòàëüíûì âîïðîñîì áèîëîãèè ðàçâèòèÿ. Çàêëþ÷åíèå Ïëþðèïîòåíòíîñòü ïîïóëÿöèé ÝÑÊ îïðåäåëÿåòñÿ àêòèâíîñòüþ ñïåöèôè÷åñêèõ òðàíñêðèïöèîííûõ ôàêòîðîâ, òàêèõ êàê Oct4, Nanog, Sox2 è íåêîòîðûõ äðóãèõ. Ýòè ôàêòîðû îáëàäàþò óíèêàëüíûìè ïàòòåðíàìè ýêñïðåññèè, è îò èõ áàëàíñà â êàæäûé ìîìåíò ýìáðèîíàëüíîãî ðàçâèòèÿ çàâèñèò êîììèòèðîâàíèå è äèôôåðåíöèðîâêà ýìáðèîíàëüíûõ ñòâîëîâûõ êëåòîê.  òî æå âðåìÿ, ñàìîîáíîâëåíèå è ïëþðèïîòåíîñòü ÝÑÊ òåñíî ñâÿçàíû ñî ñïåöèôè÷åñêèìè ìîäèôèêàöèÿìè êîâàëåíòíûõ ñâÿçåé ãèñòîíîâ ñ ÄÍÊ, à òàêæå ñòåïåíÿìè àññîöèàöèè òðàíñêðèïöèîííûõ ôàêòîðîâ ñ õðîìàòèíîì, òî åñòü ñ ýïèãåíåòè÷åñêèìè ôàêòîðàìè. Íà ïðîöåññû, ñâÿçàííûå ñ ïîääåðæàíèåì ñâîéñòâ ÝÑÊ, âëèÿåò àêòèâíîñòü íåêîòîðûõ ôåðìåíòîâ, íàïðèìåð õðîìàòèíðåìîäóëèðóþùèõ ôàêòîðîâ èç PcG-ãðóïïû, à òàêæå óðîâåíü ìåòèëèðîâàíèÿ ãèñòîíîâ è ÄÍÊ. Òàêèì îáðàçîì, íåâîçìîæíî âûäåëèòü îäèí èëè íåñêîëüêî êëþ÷åâûõ ôàêòîðîâ, îò êîòîðûõ çàâèñÿò õàðàêòåðèñòèêè ÝÑÊ. Òåì íå ìåíåå, çíàÿ âñþ ñëîæíóþ ñõåìó âçàèìîäåéñòâèé ýòèõ ôàêòîðîâ, ìîæíî ïðåäïîëàãàòü, êàê îòðàçèòñÿ èçìåíåíèå ýêñïðåññèè îäíîãî èëè íåñêîëüêèõ èç íèõ íà ñâîéñòâàõ ÝÑÊ. Êëåòî÷íàÿ òðàíñïëàíòîëîãèÿ è òêàíåâàÿ èíæåíåðèÿ Òîì III, ¹ 2, 2008 44 Îáçîðû ËÈÒÅÐÀÒÓÐÀ 1. Keller G. 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