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Induction of Pluripotency:
+ g) {. a, Z. K& g/ D( j' m# hFrom Mouse to Human
5 ^& {& T! k6 h+ n; ]; B P2 y6 J7 ~Holm Zaehres1* U2 N2 e5 Q; z# d
and Hans R. Schöler1,* C ~$ M7 a0 G9 p5 z; [
*4 Z; } N g0 v! [! F! b k3 N
1/ g3 D# d: S5 w# }6 r) E
Max Planck Institute for Molecular Biomedicine, Department of Cell and Developmental Biology, Münster, NRW 48149, Germany& ?3 O8 T- E% ?4 D9 ~3 K
*Correspondence: schoeler@mpi-muenster.mpg.de
7 o* a, M3 y1 L( W) B; mDOI 10.1016/j.cell.2007.11.020
* q, @( v& T. A1 ]' nIn this issue of Cell, Takahashi et al. (2007) transfer their seminal work on somatic cell
& j; @! Z& I+ M; u* h: {reprogramming from the mouse to human. By overexpressing the transcription factor
$ O6 v9 }8 m& xquartet of Oct4, Sox2, Klf4, and c-Myc in adult human fbroblasts, they successfully % m+ z8 {9 x0 U% y1 k# k
isolate human pluripotent stem cells that resemble human embryonic stem cells by all 8 l4 C+ N9 Q0 K- g) i
measured criteria. This is a signifcant turning point in nuclear reprogramming research
5 s: S" ?& w. uwith broad implications for generating patient-specifc pluripotent stem cells for research
n8 b& F# } x* R" wand therapeutic applications.* q, u, `8 }/ Z$ L9 q6 W
This year’s three Physiology or Medi-' E" Y/ `8 |! G+ U/ M
cine Nobel Laureates—Martin Evans,
# [! i, ?! a& n7 a6 e9 y- L* h4 nMario Capecchi, and Oliver Smithies—* s/ }9 G2 `" o# w" }
will be honored in Stockholm in 10 ; {+ [2 ] j# W x4 I/ y' N
days time for their discovery of DNA + }. B u& _3 J4 H Z( K* U- ~2 ]
recombination and the development 7 w9 y2 L2 n( j) F
of mouse embryonic stem (ES) cell
$ f, A Y4 w/ j2 |6 S) h" b- A" ]& Qtechnology. It was Martin Evans who
& F7 i% d( S' v2 Idiscovered how to make mouse ES 0 J+ u ^" F, o) `4 v
cells, enabling any genetic alteration
: F9 K3 Q0 p- Y9 E* Z! `% v- Pto be transferred to the germline and S3 l& O6 z4 a3 `
hence to the next generation (Evans ! Y# t; r- e$ N3 Q. `( t6 y
and Kaufman, 1981; Martin, 1981). $ d0 H( d% z/ t
Before this breakthrough, researchers ( N% O3 g+ R4 m% @3 E
studied mouse embryonal carcinoma + U' A- Y- t8 H) X
cells derived from tumors, which 4 {# ], P7 A) M
could form every mouse cell lineage
. H; E/ ?# F& B) D0 Gexcept the germline. Combining DNA ; D' |6 j3 J3 X0 i, [
recombination and mouse ES cell 6 f- T' y3 {$ W) s& Y( y4 L
technology revolutionized an entire
: v$ C' n ^# g1 T8 a. {( F$ bfeld of research, forming the basis for
; Y3 q& D% G8 A! cstudying and understanding the roles
5 q) T5 P% i ^8 v1 t; `9 aof numerous genes in embryonic 2 U* j. K6 ], W
development, adult physiology, dis-
* ?0 J* n* R* b. Tease, and aging. To date, more than ; w& A, ^( m) p0 p5 I' a% |
500 mouse models of human disor-$ l2 g: q2 v* {8 D8 v
ders have been generated. Now, with 7 u9 t2 g0 ]' Z4 } ~' l7 ?
the study by Takahashi et al. (2007) $ ^) I) l: p9 ]& }4 W3 N+ u
published in this issue of Cell, another
" h# y* t: ?' vimportant revolution is taking place.. N. e' x* i) `* i5 F+ v
Last summer, Takahashi and % l) I5 A9 P% q! v
Yamanaka (2006) stunned the scientifc
. e+ m+ Z! \& [) {5 l. |7 n/ Scommunity with their study showing ( W4 A5 Z: u" l6 E: \
molecular reprogramming of mouse ; m% V7 H6 y$ _7 w, w* n
somatic cells into induced pluripotent 7 z) F; d2 ]* J
stem (iPS) cells using just four factors:
5 A$ ]& Q, k. G# u& p. @Oct4, Sox2, Klf4, and c-Myc. Their
* X! d; p) Y* f0 nelegant but demanding approach of
0 b$ \* \; H- l2 y; ]! Lscreening for a cocktail of factors that 0 k0 n: S: P) H
could reprogram mouse fbroblasts / h7 {2 j- j! W
starting from 24 candidate genes paid
* D( G) K0 J( c0 D! moff with their detailed description of iPS ; ?& u' O& x( |" ]7 r# ^! P! K+ E
cells, which are almost indistinguish-# \5 X/ e$ m/ m0 ]
able from mouse ES cells. As with all
+ E/ J; ^& t. P+ K3 z- gscientifc discoveries, these exciting * d. o2 _& z) h( H
fndings had to be reproduced. Sev-
, f; u, p) A% X/ Leral studies published this year not 9 f" d! d4 d$ J: ^! \
only reproduced but also extended
, ~! j; Y3 F) |- A3 dthe Takahashi and Yamanaka fndings 1 h/ q4 c( A9 S) _& u& S U2 }
by demonstrating the pluripotency and 8 U" s% q! _. Y4 V; U7 ?6 | T* L
differentiation potential of mouse iPS 4 i: {( H2 P. C4 o. B0 a
cells in rigorous developmental assays 0 L5 H8 c# s& E9 h
(Maherali et al., 2007; Okita et al., 2007;
9 E+ @% g, [- P( v3 n& k* YWernig et al., 2007).! A4 o0 D3 q# K4 m- M$ X" g9 m
In their new study, Takahashi,
0 P& p# I" c* h9 u8 MYamanaka, and their colleagues , M) [9 X& c, L( m
(Takahashi et al., 2007) now translate
9 ~' R G C6 d# c- Gtheir remarkable fndings from mouse " w1 f1 Z! v. W4 b8 V9 K
to human (see Figure 1). They selected 9 j$ y @, [$ _
adult human dermal fbroblasts and 1 }. y2 o+ C. Z9 Z& N* Z! ^! M
two other human fbroblast popula-
$ e# w& H* |9 t# Ntions (from synovial tissue and neo-
9 b+ ~* g- H) d. Y/ enatal foreskin) from different human r4 _- N1 a0 f$ V m
donors as their reprogramming target 3 @3 ?' v8 D6 u) N
cell populations. They then trans-
+ x8 R( e7 S/ U5 t' o- {0 lduced the human fbroblast cultures
" c- ?% c- Q* T/ @, G gwith retroviral vectors carrying trans-9 R4 Q7 |2 x6 n) Q& Y8 \
genes for the human versions of Oct4,
3 \, U6 m4 ? c0 q* zSox2, Klf4, and c-Myc and cultured . @2 `( Q' y9 _) O0 Z
the cells under human ES cell culture
1 }) J) W) a% Pconditions. Thirty days after transduc-% }# n+ K+ q }+ t Z
tion, the culture plates were covered
2 B9 ]$ T% f0 m% \with human ES cell-like iPS colonies 7 A5 } G' ?9 V: {$ D' `
(among other colonies), which could
; W; C+ g4 ?* U/ X9 v1 ebe further propagated and expanded. * y5 d, A( h# @& S) K2 Z$ Y# v
The retroviral vectors enabled silenc-- E4 E7 }" |% H) F% y
ing of all four transgenes after human 8 K2 h7 D( N& B. O+ o
iPS formation (as found in the mouse
6 v& F: }. }! n* D0 Z6 Hsystem) indicating that the iPS cells
/ F9 B4 s$ D2 d; @0 ]are fully reprogrammed and no longer
+ ~. Y0 Y4 k' xdepend on transgene expression.
/ {. K9 W: K& e N9 H$ J* y4 mUnlike the mouse study, human 0 o( z" B8 ^& {- F
iPS cells were generated without any 8 q7 d: u$ m, R. ]/ G
genetic selection procedures. Given
# w5 W8 O. M4 [/ xthe lower mitotic index of human ES
; ?1 b9 F' Q/ @% w% m; Z. fcells, it is not surprising that the gen-$ v( v! R6 Q0 f
eration of human iPS cells takes nota-1 h6 m3 i; H. T# U# y' H
bly longer than in the mouse system.
8 t- T0 C# m5 a! D+ N x4 @- sThe authors subjected their human , c( o& f4 q8 L" ~$ h! G( a
iPS cells to a panel of assays to com-% D. s; A9 H) D* \2 w
pare them with human ES cells. These
) h/ X% w+ [; s7 O, {% s: iassays included morphological stud-( U! R( V2 w) G& U; t0 @
ies, surface-marker expression, epi-
+ }6 A/ `; Q& @genetic status, formation of embryoid
. s0 x2 w+ d) L* f( Ubodies in vitro, directed differentia-% d. B! Q4 M. P- m6 [3 `% J' Z
tion into neural cells and beating car-/ j4 k* d- v/ y
diomyocytes (according to human : b6 n- N# r* z1 T& N* n/ o- v, a
ES cell differentiation protocols), and ' q) ]4 @, M, p8 ?9 B
fnally teratoma formation in vivo. ) {* y5 d( @4 p1 V+ ?
DNA microarray analysis revealed
5 x0 {; A. V; e5 ythe remarkable degree of similar-1 s+ L/ F. Z# T: Z: B
ity between the global gene expres-* k4 L5 K: k# @0 l/ ^! W6 ]
sion patterns of human iPS cells and * f; F) R1 }$ w5 p. o1 j
human ES cells. Notably, genomic / D g; P* v( r% A
DNA analysis as well as analysis of
4 Q" ]0 m; Y) V6 I5 F7 }1 V" k1 Ishort tandem repeats demonstrated
( M4 o/ U- _9 ~ y% {$ X7 Q( N9 Gthe genetic origin of independent & }5 o$ H# {; R* V- Q# `( F6 Q, D
human iPS clones from their parental ) `- |, s* n; L3 K, D7 W7 t
fbroblast populations./ q5 I% Z3 s6 D& x. p e
The derivation of mouse and then
+ w7 w/ C0 b( e2 b; yhuman ES cells (Thomson et al., 1998)
H. E" O) P3 p% U+ xas the gold standard of pluripotent " H. t8 B6 [( ?
stem cell populations has necessarily
3 s! r- X7 l- ?# d3 ^/ x" y$ F( m9 j' ?led to emphasis on differences in the ! C S4 h% Q& p& D
regulation of self-renewal between 2 U( [9 @5 V! t0 ]- ]0 Y5 N8 C
mouse and human ES cells. For , q0 F5 A/ S5 |( E8 }, w3 i
example, human ES cells depend on . q) e7 u* l, X r
bFGF for self-renewal, whereas their 2 ]4 A: w1 R2 Z& d0 N# @
mouse counterparts depend on the 8 p9 h6 N' ^0 [
Lif/Stat3 pathway; BMP is involved in
+ \* L7 X$ D/ H: h% n- qmouse ES cell self-renewal, whereas * b: \0 y% P3 |$ r
in human ES cells it induces differen-
- h" \( u1 }' H8 qtiation. Extrinsic factors and signals ' T6 ~4 p$ X" u' ~
for maintaining pluripotency may dif-. `0 i8 S* d5 t4 o- r& h
fer between mouse and human. How-
# r- w3 A$ ]! U! n$ d* m% Q4 Kever, the ability to translate somatic
1 G& Z% e- o( c1 jcell reprogramming from mouse to
% O" C8 J* y. } R, b6 M5 q0 chuman using the same transcription
7 s- \% ?5 ^4 b7 m, O3 ^6 \! F; ~factor quartet further emphasizes the
, R" E1 |' k1 L5 Z. s% \conserved nature of the Oct4/Sox2
& [+ \6 Z7 J# F0 l) ~transcription factor network that
- C q" e/ U% |. [5 W5 ~controls self-renewal of mouse and / B, H' X- h8 g
human ES cells (Boyer et al., 2005).
' G4 N& F5 a8 r2 c3 LGiven that Klf4 and c-Myc are chro-
/ z5 ~( \+ l: ]$ r, v+ wmatin modifers and can immortal-
8 d+ ?7 v( r& xize cells, one might be able to fnd
$ G9 w7 j! s! _/ g" B: A7 Gother factors or small molecules that
( h& f4 Q1 f! x# G) p* q0 _could replace these two factors in the
& G1 j2 Y+ C/ f$ @2 Kcocktail (Yamanaka, 2007). In these 8 M8 Q. s: O1 _+ d* p3 ]8 A. j
studies, the possibility of retroviral
5 P E; E8 D) Z# m Iinsertional mutagenesis, resulting
- O1 ~$ |" ^1 t7 N" Din the activation of other genes con-" k' e( T7 f' i9 `
tributing to reprogramming, cannot 8 C& f `2 K7 m8 D
be excluded, providing an opportu- o; f" {4 }2 ^1 s# V6 U
nity to potentially identify new repro-
# R6 b& T: I1 H0 [8 F' U' X: ugramming factors beyond the cur-; E9 i& O, V& S$ F% h) g! M/ i
rent quartet. Also, taking a broader % o+ g' W9 B+ a( F# I+ J
screening approach for reprogram-) Q( ^9 a7 N& @* L
ming human fbroblasts (as Takahashi % k3 y$ V; v" Q- s- i/ N
and Yamanaka did for their mouse
8 D- h7 }* U3 |8 ^2 ~study) might yield other combinations
% H$ j$ Q; `% Z3 e; }of reprogramming factors.
4 e2 `1 ^" z# Z1 lDirect reprogramming of somatic 2 K2 ^7 n& x) z5 O- t' J
cells to a pluripotent state, thus revers-( M$ |- g5 G/ B# c0 l5 n( k/ H6 ~
ing the developmental arrow of time, 0 r$ k7 f7 z2 x0 {# e
is considered by some to be the “holy ! v0 W+ c$ w1 i. |# S+ }
grail” of stem cell research. Once the 5 y: }- `: G) t3 f
results in human cells are confrmed, ! P1 @( M* s2 n* {
these advances will enable the cre-! m9 Y" ^2 E/ t3 P, s
ation of patient-specifc stem cell lines
! d* P6 Q0 t$ x4 oto study different disease mechanisms 4 Z# N p3 [; A; t. r4 e) i' O) O
in the laboratory. Such cellular models
: Y- w) C% ~* falso have the potential to dramatically 9 Z0 Z7 h5 L. U b
increase the effciency of drug discov-
; {% Q% C& E. G8 b- _' Sery and to provide valuable tools for
C: N( O4 Z1 {+ Y' z$ Otoxicology testing. Furthermore, this ^6 K* y' \8 Z3 r( H" e( t
reprogramming system could make 8 W) h* o8 ]/ v$ h) D
the idea of customized patient-specifc
% H+ F0 D; S3 Q& Q. `screening and therapy both possible
; |1 R" h: E% ]# k* ~+ ~7 \and economically feasible. Finally, the 6 {+ A4 U& [- W4 z: c
work will have a powerful impact on
: ~1 F$ O- \: \: v1 [& Gthe intense debate regarding the moral, . U& _; f4 v' j2 P- p3 e
religious, and political aspects of ES cell 5 W5 j# \, @' J! Q
research. However, a big mistake now ) r5 p0 S% n! |2 o! }% y
would be to consider human ES cells % [' r) ~ @1 P
obsolete. There are still many hurdles 9 h% R5 Y/ p! w" d9 R5 I6 a3 P
to overcome before we ful ly understand % E5 I" y- `' v3 \( r0 T) S4 i
pluripotency and before we have human 1 |9 {" {6 H) S0 T; R" f4 M; [
iPS cells in hand that are suitable for 2 `- n( p; r: F$ _6 G
therapeutic application. For example,
; W1 e& D2 \; A( {- G& R' _: ea signifcant proportion of mice derived . `% W- N- h0 E# _
from mouse iPS cells develop tumors
% p3 Q, ^8 D1 p" f8 A& C3 \due to reactivation of the c-Myc retro-
: m0 F9 K( M4 J9 _ h5 N: f Yvirus (Okita et al., 2007) compared to
6 n" @" H( N$ {* jmice derived from ES cells, which are
+ d# V% F+ ]: K' O, Ynormal. The search is now on to fnd a " z" U& Y% |. K M) [
way to reprogram somatic cells without
D1 P$ Q/ g1 Qretroviruses and maybe even using a
2 p; M4 R8 v* I* w& X7 Ecocktail of small molecules. Given this,
3 O5 M! I; \$ oit should be emphasized that human
+ h9 w% h* m3 {ES cell research is more important than ' \4 X+ L$ ~: H0 L+ S8 q9 Z
ever for it will shed light on how iPS
: [% {% h2 a& M7 J( I* S" u5 n' h1 Rcells can best be maintained in their . i0 n/ K! p$ m" U
pluripotent state and how they can be 3 l+ w, I4 L/ u6 H" {% R
induced to differentiate into the cell # H M4 u5 R2 i& N* p
lineage of interest. The feld of nuclear 6 r' \/ y+ S5 [3 I$ s/ Z D
reprogramming has come a long way 0 B3 A2 J* @; i0 ], U) Q4 T8 A
from the initial nuclear transplantation
5 h" Y6 }: W8 J% a1 D8 `# v* Istudies in frogs 50 years ago, to the 5 S8 ^+ m" F# ?$ `! t
birth of Dolly, the frst mammal cloned
8 f9 e1 j# R8 U3 W7 F1 x Nfrom adult somatic cells (Wilmut et al., * ^/ Y T, N! P4 C: K
1997), to the fallout from the fabricated
+ f) |3 ]% E! _human nuclear transfer experiments , b1 D% W+ I5 S* ]5 g- d* x* m
of several years ago, to the landmark , [, a/ ]; s9 x, o# C+ }! Q
studies of Takahashi, Yamanaka, and
9 \, h4 l* t" O8 }- mtheir colleagues, frst in mice and now
: L3 a0 f: g+ x. S7 s6 B/ {in humans.4 d2 n5 t6 t6 F7 y" o
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发表于 2009-4-28 21:35
发表于 2009-5-16 10:41
