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Induction of Pluripotency:
- l$ a# P9 H9 T4 B6 k6 N. ^, dFrom Mouse to Human
/ K' Q+ _7 R* XHolm Zaehres1
$ j# A; m) y% m; p/ s5 l2 D6 s9 d and Hans R. Schöler1,
$ e9 ~/ C9 X. u3 n*- e) ]3 ^/ B' i D3 D% T
10 o. R3 V( _4 u8 d
Max Planck Institute for Molecular Biomedicine, Department of Cell and Developmental Biology, Münster, NRW 48149, Germany8 r( ?, y: y1 Y, }6 m
*Correspondence: schoeler@mpi-muenster.mpg.de E: v: m1 h6 j' [' X
DOI 10.1016/j.cell.2007.11.0203 T4 L( Q1 H$ p$ s5 E9 x
In this issue of Cell, Takahashi et al. (2007) transfer their seminal work on somatic cell
L% B5 n* s! ` Greprogramming from the mouse to human. By overexpressing the transcription factor
4 U, M7 {7 O% E" ]9 R. H( L, jquartet of Oct4, Sox2, Klf4, and c-Myc in adult human fbroblasts, they successfully
: @/ L; x6 b& D; e5 W3 F% [isolate human pluripotent stem cells that resemble human embryonic stem cells by all 8 w' i- d7 M( `
measured criteria. This is a signifcant turning point in nuclear reprogramming research
( R% i/ E9 y& t$ s* `& A- vwith broad implications for generating patient-specifc pluripotent stem cells for research
# M# [4 S% u% p2 ?+ Jand therapeutic applications.
% p; ~ q6 J+ f& v2 lThis year’s three Physiology or Medi-
# f {* E- {4 _2 C- H: Lcine Nobel Laureates—Martin Evans,
- V* k$ _2 n% gMario Capecchi, and Oliver Smithies—
L8 L' d# J/ l" M0 S1 mwill be honored in Stockholm in 10
3 p% z& c7 z* D$ Y7 jdays time for their discovery of DNA 8 O/ E: N6 O7 w
recombination and the development
* Z+ t5 T- Q% t- j8 I8 a/ W. A3 Xof mouse embryonic stem (ES) cell
( ]7 `& r# A$ etechnology. It was Martin Evans who B$ G2 U0 w. n' y0 g* c, |
discovered how to make mouse ES
0 P9 u, e, b( A1 N5 X7 W3 \0 lcells, enabling any genetic alteration
8 {) G5 H7 k7 e$ o u v1 I5 R# eto be transferred to the germline and " m% S, Z! z2 v8 Q5 w2 R
hence to the next generation (Evans
! d6 C7 J( [1 f& q' Uand Kaufman, 1981; Martin, 1981). 4 N1 Z6 O0 R' X! n9 n+ k/ Q; h
Before this breakthrough, researchers
0 r( j8 p! L$ Y- @/ Q) g7 b sstudied mouse embryonal carcinoma & G) Y! N+ c) X1 g
cells derived from tumors, which
& V* X( R' U- E; `could form every mouse cell lineage
2 U1 c0 o( B" d/ P; ~! fexcept the germline. Combining DNA
7 p7 V0 N" X1 L' l! erecombination and mouse ES cell
% [" Y& i. `7 F, Ntechnology revolutionized an entire 5 ]& e8 q1 }) O; @- ^
feld of research, forming the basis for
7 o- B# m* u- n' Qstudying and understanding the roles
! z% k* q: \1 \( {, x. s7 K' Zof numerous genes in embryonic / W& P& u8 V# j% J8 q# S& a5 W0 H
development, adult physiology, dis-7 t1 |, D" V+ {8 F s: |
ease, and aging. To date, more than + `: C" @5 [& t( e1 W5 E2 a
500 mouse models of human disor-+ y6 |" p$ a* e
ders have been generated. Now, with 8 E- b. R) a; z1 r
the study by Takahashi et al. (2007)
' g% P! x. r( n* }1 _published in this issue of Cell, another
, A& C" m/ J# ?( |- simportant revolution is taking place.
% a3 z: ~) X" A1 Q2 U! f9 T# }, \Last summer, Takahashi and % w- v, u& ], n
Yamanaka (2006) stunned the scientifc
5 F# g: D: o/ Acommunity with their study showing
% z. |( ~! m" d1 ?+ xmolecular reprogramming of mouse 8 S* o+ t( i5 x' M* k$ u
somatic cells into induced pluripotent * U9 a. G. c2 u% A5 e* I; ~6 D
stem (iPS) cells using just four factors:
" V$ v, [% e9 wOct4, Sox2, Klf4, and c-Myc. Their
4 ^* d3 O7 O( q5 B( D) Zelegant but demanding approach of
4 ?0 Z9 a: G, Y& v' wscreening for a cocktail of factors that - @# p! _' Y, W2 d4 M d+ ^, r0 F
could reprogram mouse fbroblasts
* O( k: z) W$ I4 y8 {8 pstarting from 24 candidate genes paid
* i6 E% r; {# M) t! ]off with their detailed description of iPS
3 {/ Y; ]& N6 V7 _cells, which are almost indistinguish-
: F- O( `6 h3 _. e j$ ]able from mouse ES cells. As with all
1 X+ y( q8 V" u- S+ r( jscientifc discoveries, these exciting 2 F+ A( q6 d' T7 a0 J
fndings had to be reproduced. Sev-, Z4 V+ O: V" z `
eral studies published this year not
1 i% K: u/ I+ y3 konly reproduced but also extended
3 P. p" c0 {/ X5 c; C) N3 ythe Takahashi and Yamanaka fndings
# x% m ] \, j9 s1 [by demonstrating the pluripotency and 5 F+ b" ~; e$ E. ^3 k% n: X
differentiation potential of mouse iPS 4 o- f- i! p$ K5 ~# R: ?% Z
cells in rigorous developmental assays & k2 ~. N' d3 K6 A
(Maherali et al., 2007; Okita et al., 2007; 1 ~' y( {' D! c. l
Wernig et al., 2007).
# A; }1 o/ m8 a, x8 E( fIn their new study, Takahashi,
" T" x* D# p+ D3 y/ p/ h- fYamanaka, and their colleagues
. ^- B) K4 z; ]+ h(Takahashi et al., 2007) now translate * y% p7 o) I: f1 G! a
their remarkable fndings from mouse : @' n! z5 E2 \. G* Q' {1 y
to human (see Figure 1). They selected
5 Z8 D4 Y' a4 ?0 T6 n. w0 p& eadult human dermal fbroblasts and / n* ^1 b2 t* T8 X- d" r8 _# q
two other human fbroblast popula-
: W# Y9 y% Y& y5 M* x w8 ~9 htions (from synovial tissue and neo-
/ R6 ?) H9 N5 M' v, f: nnatal foreskin) from different human 9 c7 N' Z' I6 j7 @
donors as their reprogramming target
! [6 b1 [ _+ l/ P" wcell populations. They then trans-: O$ H5 W$ U% u3 c a
duced the human fbroblast cultures $ g9 a0 l! G9 Q/ }- l
with retroviral vectors carrying trans-
; _8 l2 q# X6 D( ^$ H- agenes for the human versions of Oct4,
1 g, B4 I" Z7 _7 W/ T9 mSox2, Klf4, and c-Myc and cultured
; Z, S1 S5 r$ W1 dthe cells under human ES cell culture ' O, C: |% U" v- `
conditions. Thirty days after transduc-* O" ~2 z0 K1 k: {9 M
tion, the culture plates were covered
) k G3 }3 S* \: x9 Q# Fwith human ES cell-like iPS colonies 3 j" @8 K. L! h# v
(among other colonies), which could 4 c7 ^8 J' U( c* r" ^# N2 }$ J
be further propagated and expanded.
) C: ^7 k0 u, M( N/ [The retroviral vectors enabled silenc- ?$ |4 u( {; o* ~" M
ing of all four transgenes after human 3 S9 V& e1 x/ @, E' p8 W3 l
iPS formation (as found in the mouse
) p& W5 n( \) Z7 W8 r6 ~system) indicating that the iPS cells
9 S( C( g" h. ^9 \ d% Aare fully reprogrammed and no longer
% ?& A8 O4 D9 F3 J0 \, m3 Ddepend on transgene expression.
( l4 l s9 Y: t" QUnlike the mouse study, human
0 S ]* W& ~" m# [' y6 niPS cells were generated without any 4 g4 H4 A. {7 b9 _/ \& Z' n
genetic selection procedures. Given / i) f0 G/ M- a1 v- a9 T
the lower mitotic index of human ES
# @, @$ @# S5 C' wcells, it is not surprising that the gen-
' d- q+ U9 V9 [ {0 keration of human iPS cells takes nota-6 m1 L9 r7 k& g, M5 |
bly longer than in the mouse system. 3 S. L6 }/ T5 n' b/ a; Z/ e
The authors subjected their human
& d+ j) d3 w. J, w5 NiPS cells to a panel of assays to com-
$ `& e8 ^$ a( ^" f7 }: Jpare them with human ES cells. These % d; z/ P# y6 w
assays included morphological stud-
- q. }. p- Q, U& ries, surface-marker expression, epi-
9 M" l$ M k. q: egenetic status, formation of embryoid
' b. X2 u* F1 m1 j8 p# E: zbodies in vitro, directed differentia-* ^: b. n6 I$ c7 i7 r
tion into neural cells and beating car-
3 D, `% [/ Z5 s% z: `5 D# Q" pdiomyocytes (according to human 3 b# ^/ p. ]7 F' A* f' \4 n9 v4 ~
ES cell differentiation protocols), and
0 v1 K+ |" a1 Q8 a y: N0 ?. Afnally teratoma formation in vivo. 5 e* N2 a" O2 U- _* d. v* o7 p# V
DNA microarray analysis revealed
/ Z4 G6 Z2 X7 k' r jthe remarkable degree of similar-' y: A: f$ Y4 ]* V5 @6 D" Y& w: r1 W
ity between the global gene expres-! T( J/ V% g* N1 n4 V4 w3 u
sion patterns of human iPS cells and
( b1 j/ L* ?! [/ k! khuman ES cells. Notably, genomic 2 c5 a; I0 U. x y% R" t3 G- R# M
DNA analysis as well as analysis of
: x1 L8 e/ W2 v5 ^short tandem repeats demonstrated
# C7 l+ M' f8 R+ c. ^/ ?% |the genetic origin of independent 1 p7 F# k$ J9 o3 N5 `( |+ B
human iPS clones from their parental 0 J/ h x$ P m* b' ^* k8 f
fbroblast populations.' N; P0 `" Y5 R7 C
The derivation of mouse and then ) u/ ]1 M) X0 A8 o+ B1 C
human ES cells (Thomson et al., 1998) 9 e( G y6 \" e7 I
as the gold standard of pluripotent
' d* I& ]" ^: F- Q" `stem cell populations has necessarily
$ z2 v8 k8 ~1 @led to emphasis on differences in the + L6 P. _& d5 L8 @0 T) a
regulation of self-renewal between # s) g1 I5 w o, W+ z+ a
mouse and human ES cells. For 8 \$ e* ?! A9 \# P* m( n
example, human ES cells depend on . L9 p4 {( j3 o: b
bFGF for self-renewal, whereas their & {4 q C ^: x* v* z: d/ {
mouse counterparts depend on the
0 x6 \. B: p! M9 ELif/Stat3 pathway; BMP is involved in
& [. f$ R, [; c5 Zmouse ES cell self-renewal, whereas & F! n* S$ R j K1 n
in human ES cells it induces differen-
2 p8 o5 r/ J1 d% c' Q7 I$ utiation. Extrinsic factors and signals
- ]0 c8 H& t4 K& n% b( M gfor maintaining pluripotency may dif-. r$ [2 f4 ^8 F4 N' m
fer between mouse and human. How-; I" t8 p' r7 i+ z
ever, the ability to translate somatic
2 J: a. |9 j$ @0 K+ B- m" p1 r2 _cell reprogramming from mouse to ) `; z& J; I. ^1 t
human using the same transcription
0 b: l' d5 N. B, Cfactor quartet further emphasizes the
" O5 X, t9 ~1 @$ ]/ Oconserved nature of the Oct4/Sox2
) \8 {/ l& @$ t5 }9 k4 L# T) A ctranscription factor network that / [( @" n3 m C. d2 A8 r& K' ~, o
controls self-renewal of mouse and
9 | z, S3 ]. o9 Q7 w, b6 @human ES cells (Boyer et al., 2005).
9 Z$ `0 `4 N1 \" e! @' ~Given that Klf4 and c-Myc are chro-
+ f7 O$ F5 a' G3 `9 x" n5 v$ Q2 j, }matin modifers and can immortal-6 j' S- U5 F4 ]: K9 V* {' ]
ize cells, one might be able to fnd 5 p- p. K0 |8 L' V1 {* c
other factors or small molecules that
4 v+ p5 R' v& n* ncould replace these two factors in the 7 D, a* _, i3 D9 |
cocktail (Yamanaka, 2007). In these & b# M- }& _; Z; B: h" C
studies, the possibility of retroviral # r' J" A, ~6 D- ~
insertional mutagenesis, resulting 6 v* T7 T, M6 S" F7 e7 a
in the activation of other genes con-) b1 a& x4 a; W2 M, E/ U2 F0 B
tributing to reprogramming, cannot / G# \7 L+ |9 A4 b% f& f: Y9 a
be excluded, providing an opportu-
6 F8 [# ?$ e r$ B+ k, Lnity to potentially identify new repro-' }8 ?. u, i; p( s, P
gramming factors beyond the cur-
( ?) A1 O. L0 ]; x0 Q0 Crent quartet. Also, taking a broader / s2 g o8 g9 l; C
screening approach for reprogram-
g8 [# ]( ^/ _* `- Xming human fbroblasts (as Takahashi
9 Z% j1 y2 ]3 p5 j6 F: land Yamanaka did for their mouse
3 F1 k) z9 K1 B9 g. |& j5 Tstudy) might yield other combinations / I: u3 @! t/ Y5 V: \
of reprogramming factors." u d3 F+ Y j f; Y6 ]
Direct reprogramming of somatic ' O. A+ I% t7 \/ m
cells to a pluripotent state, thus revers-
, l& r9 U% w% fing the developmental arrow of time, ( W y$ }# @% R/ u/ d
is considered by some to be the “holy " C! e; g& R, l& y, M
grail” of stem cell research. Once the ) V( ?( z0 h2 @- f
results in human cells are confrmed, 7 j t/ G- ?# f; d$ C
these advances will enable the cre-9 c$ v6 \9 i h0 Q5 m
ation of patient-specifc stem cell lines
6 {6 \( P- Y% A+ ]to study different disease mechanisms $ u7 Q" C$ o3 P/ m0 Y8 R, j8 n
in the laboratory. Such cellular models ) w r0 K4 V9 O2 j
also have the potential to dramatically + T0 j$ [5 L) ?& @2 S, Z5 F
increase the effciency of drug discov-; }. l7 z" J) f$ J" _( c
ery and to provide valuable tools for 9 }. |5 q+ o i) E
toxicology testing. Furthermore, this
" r3 U" v. F3 P, Ireprogramming system could make
9 |; O% k) \: H" Z3 v0 Z: Jthe idea of customized patient-specifc
( n* U$ K5 n6 {% O9 k# Oscreening and therapy both possible 3 ~- [: x8 r3 N$ e. {
and economically feasible. Finally, the
8 {$ N+ g7 ] c: c9 n Uwork will have a powerful impact on
v2 y- V, b9 I# h ~; s; S, mthe intense debate regarding the moral, % ^% {, y/ @' G% z7 ^) O
religious, and political aspects of ES cell ! K6 }, i$ ?5 w8 C+ r2 ~3 Y; S0 n
research. However, a big mistake now
$ j# ^- F. E* e, _1 G0 owould be to consider human ES cells
6 M N) {! Q l: u% z6 L- tobsolete. There are still many hurdles
5 O# X. n# `: ?8 H0 N# J. Rto overcome before we ful ly understand 1 {3 ~. x/ u2 P
pluripotency and before we have human
2 f' ^" u! [8 _# HiPS cells in hand that are suitable for
6 `1 N! s1 T# \) Qtherapeutic application. For example,
3 D+ ?+ G# e1 t0 Ba signifcant proportion of mice derived
) N. @8 [" c" l) qfrom mouse iPS cells develop tumors
9 M( V; O: T3 O! C) V% [due to reactivation of the c-Myc retro-
, q% [( Q- F. M' D4 _virus (Okita et al., 2007) compared to 9 A! w+ y8 N! r
mice derived from ES cells, which are
% |; _$ B! A0 o- ~! V1 _normal. The search is now on to fnd a ; o$ |! `) ]8 w
way to reprogram somatic cells without
. m4 t8 W, E+ [9 q- P7 kretroviruses and maybe even using a
( ~ q. _7 t6 n2 x- H& h! ~9 Ucocktail of small molecules. Given this,
5 Z% h. U" U# U+ y/ I ?! }2 jit should be emphasized that human
% [3 ?( F, v$ T: xES cell research is more important than , c5 D# G* l. Q+ [' c8 N- K! O9 X1 w
ever for it will shed light on how iPS
: i% W! b+ r e! y' Y+ T bcells can best be maintained in their
8 m& T* ]4 W! s! }pluripotent state and how they can be
" J5 y+ g! }/ }+ U1 m! v/ u4 A# qinduced to differentiate into the cell
+ j- v* F& }7 L1 Alineage of interest. The feld of nuclear ! }" D1 }6 a2 V9 }) ?- T8 F
reprogramming has come a long way
# N0 Z/ ^& z/ pfrom the initial nuclear transplantation - K3 ] D: r/ j% I; }( E, X
studies in frogs 50 years ago, to the 4 w( o0 J; z7 @* L; Y
birth of Dolly, the frst mammal cloned
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发表于 2009-4-28 21:35
发表于 2009-5-16 10:41
