▁don or ▁cells ▁into ▁en uc le ated ▁p ig ▁o ocy tes . ▁Moreover , ▁N CS U 2 3 ▁medium , ▁which ▁was ▁designed ▁for ▁in ▁vit ro ▁culture ▁of ▁p ig ▁emb ry os , ▁was ▁able ▁to ▁support ▁the ▁in ▁vit ro ▁development ▁of ▁cattle , ▁m ice , ▁and ▁ch icken ▁i SC NT ▁emb ry os ▁up ▁to ▁the ▁bl asto c yst ▁stage . ▁Furthermore , ▁ov ine ▁o ocy te ▁cy top last ▁may ▁be ▁used ▁for ▁rem od eling ▁and ▁re programming ▁of ▁human ▁som atic ▁cells ▁back ▁to ▁the ▁emb ry onic ▁stage . ▁ ▁Lim itations ▁ ▁SC NT ▁can ▁be ▁in efficient . ▁Str esses ▁placed ▁on ▁both ▁the ▁egg ▁cell ▁and ▁the ▁introduced ▁nucle us ▁in ▁early ▁research ▁were ▁enorm ous , ▁resulting ▁in ▁a ▁low ▁percentage ▁of ▁successfully ▁re program med ▁cells . ▁For ▁example , ▁in ▁ 1 9 9 6 ▁Dol ly ▁the ▁sheep ▁was ▁born ▁after ▁ 2 7 7 ▁eggs ▁were ▁used ▁for ▁SC NT , ▁which ▁created ▁ 2 9 ▁vi able ▁emb ry os . ▁Only ▁three ▁of ▁these ▁emb ry os ▁surv ived ▁until ▁birth , ▁and ▁only ▁one ▁surv ived ▁to ▁ad ul th ood . ▁As ▁the ▁procedure ▁was ▁not ▁autom ated , ▁but ▁had ▁to ▁be ▁performed ▁manually ▁under ▁a ▁mic ros cope , ▁SC NT ▁was ▁very ▁resource ▁int ensive . ▁The ▁bio chem istry ▁involved ▁in ▁re programming ▁the ▁differenti ated ▁som atic ▁cell ▁nucle us ▁and