XIPOU 2, a member of the class III POU-domain family, is expressed initially at mid-blastula transition (MBT) and during gastrulation in the entire marginal zone mesoderm, including Spemann's Organizer (the Organizer). To identify potential targets of XIPOU 2, the interaction of XIPOU 2 with other genes co-expressed in the Organizer was examined by microinjecting XIPOU 2's mRNA into the lineage of cells that contributes to the Organizer, head mesenchyme and prechordal plate. XIPOU 2 suppresses the expression of a number of dorsal mesoderm-specific genes, including gsc, Xlim-1, Xotx2, noggin and chordin, but not Xnot. As a consequence of the suppression of dorsal mesoderm gene expression, bone morphogenetic factor-4 (Bmp-4), a potent inducer of ventral mesoderm, is activated in the Organizer. Gsc is a potential target of XIPOU 2. XIPOU 2 is capable of binding a class III POU protein binding site (CATTAAT) that is located within the gsc promoter, in the activin-inducible (distal) element. Furthermore, XIPOU 2 suppresses the activation of the gsc promoter by activin signaling. At the neurula and tailbud stages, dorsoanterior structures are affected: embryos displayed micropthalmia and the loss of the first branchial arch, as detected by the expression of pax-6, Xotx2 and en-2. By examining events downstream from the Wnt and chordin pathways, we determined that XIPOU 2, when overexpressed, acts specifically in the Organizer, downstream from GSK-3beta of the Wnt pathway and upstream from chordin. The interference in dorsalizing events caused by XIPOU 2 was rescued by chordin. Thus, in addition to its direct neuralizing ability, in a different context, XIPOU 2 has the potential to antagonize dorsalizing events in the Organizer.

REFERENCES

Ault
K. T.
,
Dirksen
M.-L.
,
Jamrich
M.
(
1996
).
A novel homeobox gene PV.1 mediates induction of ventral mesoderm in Xenopus embryos.
Proc. Natl. Acad. Sci. USA
93
,
6415
6420
Bauer
D. V.
,
Huang
S.
,
Moody
S. A.
(
1994
)
The cleavage stage origin of Spemann's Organizer: analysis of the movements of blastomere clones before and during gastrulation in Xenopus.
Development
120
,
1179
1189
Bermingham
J. R.
Jr.
,
Scherer
S. S.
,
O'Connell
S.
,
Arroyo
E.
,
Kalla
K. A.
,
Powell
F. L.
,
Rosenfeld
M. G.
(
1996
)
Tst-1/Oct-6/SCIP regulates a unique step in peripheral myelination and is required for normal respiration.
Genes and Development
10
,
1751
1762
Bhat
K. M.
,
Schedl
P.
(
1994
)
The Drosophila miti-mere gene, a member of the POU family is required for the specification of the RP2/sibling lineage during neurogenesis.
Development
120
,
1483
1501
Blitz
I. L.
,
Cho
K. W.
(
1995
)
Anterior neuroectoderm is progressively induced during gastrulation: the role of the Xenopus homeobox gene orthodenticle.
Development
121
,
993
1004
Blumberg
B.
,
Wright
C. V. E.
,
de Robertis
E. M.
,
Cho
K. W. Y.
(
1991
)
Organizer-specific homeobox genes in Xenopus laevis embryos.
Science
253
,
194
196
Carnac
G.
,
Kodjabachian
L.
,
Gurdon
J.B.
,
Lemaire
P.
(
1996
)
The homeobox gene Siamois is a target of the Wnt dorsalization pathway and triggers organiser activity in the absence of mesoderm.
Development
122
,
3055
3065
Cho
K. W. Y.
,
Blumberg
B.
,
Steinbeisser
J.
,
De Robertis
E. M.
(
1991
)
Molecular nature of Spemman's organizer: the role of the Xenopus homeobox gene goosecoid.
Cell
67
,
1111
1120
Cunliffe
V.
,
Smith
J.
(
1994
)
Specification of mesodermal pattern in Xenopus laevis by interactions between Brachyury, noggin and Xwnt-8.
EMBO J
13
,
349
359
Dale
L.
,
Howes
G.
,
Price
B. M.
,
Smith
J. C.
(
1992
)
Bone morphogenetic protein 4: a ventralizing factor in early Xenopus development.
Development
115
,
573
585
Detrick
R. J.
,
Dickey
D.
,
Kintner
C. R.
(
1990
)
The effects of cadherin misexpression on morphogenesis in Xenopus embryos.
Neuron
4
,
493
506
Dirksen
M. L.
,
Jamrich
M.
(
1992
)
A novel, activin-inducible, blasopore lip-specific gene of Xenopus laevis contains a fork head DNA binding domain.
Genes Dev
6
,
599
608
Espeseth
A.
,
Johnson
E.
,
Kintner
C.
(
1995
)
Xenopus F-cadherin, a novel member of the cadherin family of cell adhesion molecules, is expressed at boundaries in the neural tube.
Mol. Cell Neurosci
6
,
199
211
Fainsod
A.
,
Steinbeisser
H.
,
De Robertis
E. M.
(
1994
)
On the function of BMP-4 in patterning the marginal zone of the Xenopus embryo.
EMBOJ
13
,
5015
5025
Finney
M.
,
Ruvkun
G.
(
1990
)
The unc-86 gene product couples cell lineage and cell identity in C. elegans.
Cell
63
,
895
905
Gont
L. K.
,
Fainsod
A.
,
Kim
S.-H.
,
de Robertis
E. M.
(
1996
)
Overexpression of the homeobox gene Xnot-2 leads to notochord formation in Xenopus.
Dev. Biol
174
,
174
178
Green
J. B. A.
(
1994
)
Roads to neuralness: embryonic neural induction as depression of a default state.
Cell
77
,
317
320
Harland
R. M.
(
1991
)
In situ hybridization: An improved whole-mount method for Xenopus embryos.
Methods in Cell Biol
36
,
685
695
Hawley
H. B. S.
,
Wunnenberg-Stapleton
K.
,
Hashimoto
C.
,
Laurent
M. N.
,
Watabe
T.
,
Blumberg
B. W.
,
Cho
K. W. Y.
(
1995
)
Disruption of BMP signals in embryonic Xenopus ectoderm leads to direct neural induction.
Genes Dev
9
,
2923
2935
He
X.
,
Saint-Jeannet
J.-P.
,
Woodgett
J. R.
,
Varmus
H. E.
,
Dawid
I. B.
(
1995
)
Glycogen synthase kinase-3 and dorsoventral patterning in Xenopus embryos.
Nature
374
,
617
622
Hemmati-Brivanlou
A.
,
de la Torre
J. R.
,
Holt
C.
,
Harland
R. M.
(
1991
)
Cephalic expression and molecular characterization of Xenopus En-2.
Development
111
,
715
724
Hemmati-Brivanlou
A.
,
Melton
D. A.
(
1992
)
A truncated activin receptor inhibits mesoderm induction and formation of axial structures in Xenopus embryos.
Nature
359
,
609
614
Hemmati-Brivanlou
A.
,
Kelly
O. G.
,
Melton
D. A.
(
1994
)
Follistatin, an antagonist of activin is expressed in the Spemann organizer and displays direct neuralizing activity.
Cell
77
,
283
295
Jaegle
M.
,
Mandemakers
W.
,
Broos
L.
,
Zwart.
R.
,
Karis
A.
,
Visser
P.
,
Grosveld
F.
,
Meijer
D.
(
1996
)
The POU factor Oct-6 and Schwann cell differentiation.
Science
273
,
507
510
Jones
C. M.
,
Lyons
K. M.
,
Lapan
P. M.
,
Wright
C. V. E.
,
Hogan
B. L. M.
(
1992
)
DVR-4 (Bone morphogenetic protein-4) as a posterior-ventralizing factor in Xenopus mesoderm induction.
Development
115
,
639
647
Jones
C. M.
,
Kuehn
M. R.
,
Hogan
B. L. M.
,
Smith
J. C.
,
Wright
C. V. R. E.
(
1995
)
Nodal-related signals induce axial mesoderm and dorsalize mesoderm during gastrulation.
Development
121
,
3651
3662
Kessler
D. S.
,
Melton
D. A.
(
1995
)
Induction of dorsal mesoderm by soluble, mature Vg1 protein.
Development
121
,
2155
2164
Knecht
A. K.
,
Good
p. J.
,
Dawid
I. B.
,
Harland
R. M.
(
1995
)
Dorsal-ventral patterning and differentiation of noggin-induced neural tissue in the absence of mesoderm.
Development
121
,
1927
1936
Ladher
R.
,
Mohun
T. J.
,
Smith
J. C.
,
Snape
A. M.
(
1996
)
Xom: a Xenopus homeobox gene that mediates the early effects of BMP-4.
Development
122
,
2385
2395
Lamb
T. M.
,
Knecht
A. K.
,
Smith
W. C.
,
Stachel
S. E.
,
Economides
A. N.
,
Stahl
N.
,
Yancopolous
G. D.
,
Harland
R. M.
(
1993
)
Neural induction by the secreted polypeptide noggin.
Science
262
,
713
718
Lee
J. E.
,
Hollenberg
S. M.
,
Snider
L.
,
Turner
D. L.
,
Lipnick
N.
,
Weintraub
H.
(
1995
)
Conversion of Xenopus ectoderm into neurons by NeuroD, a basic helix-loop-helix protein.
Science
268
,
836
844
Lemaire
P.
,
Garrett
N.
,
Gurdon
J. B.
(
1995
)
Expression cloning of Siamois, a Xenopus homeobox gene expressed in dorsal vegetal cells of blastulae and able to induce a complete secondary axis.
Cell
81
,
85
94
Lemaire
P.
,
Kodjabachian
L.
(
1996
)
The vertebrate organizer: structure and molecules.
Trends in Genet
12
,
525
531
Li
P.
,
He
X.
,
Gerrero
M. R.
,
Mok
M.
,
Aggarwal
A.
,
Rosenfeld
M. G.
(
1993
)
Spacing and orientation of bipartite DNA-binding motifs as potential functional determinants for POU domain factors.
Genes and Development
7
,
2483
2496
Moos
M.
Jr.
,
Wang
S.
,
Krinks
M.
(
1995
)
Anti-dorsalizing morphogenetic protein is a novel TGF-homolog expressed in the Spemman organizer.
Development
121
,
4293
4301
Nakai
S.
,
Kawano
H.
,
Yudate
T.
,
Nishi
M.
,
Kuno
J.
,
Nagata
A.
,
Jishage
K. J.
,
Hamada
H.
,
Fujii
H.
,
Kawamura
K.
,
Shiba
K.
,
Noda
T.
(
1995
)
The POU domain transcription factor Brn-2 is required for the determination of specific neuronal lineages in the hypothalamus of the mouse.
Genes Dev
9
,
3109
3121
Newport
J.
,
Kirschner
M.
(
1982
)
A major developmental transition in early Xenopus embryos.
Cell
30
,
687
696
Pannese
M.
,
Polo
C.
,
Andreazzoli
M.
,
Vignali
R.
,
Kablar
B.
,
Barsacchi
G.
,
Boncinelli
E.
(
1995
)
The Xenopus homologue of Otx2 is a maternal homeobox gene that demarcates and specifies anterior body regions.
Development
121
,
707
720
Piccolo
S.
,
Sasai
Y.
,
Lu
B.
,
De Robertis
E. M.
(
1996
)
Dorsoventral patterning in Xenopus: inhibition of ventral signals by direct binding of chordin to BMP-4.
Cell
86
,
589
598
Pierce
S. B.
,
Kimelman
D.
(
1995
)
Regulation of Spemann organizer function by the intracellular kinase Xgsk-3.
Development
121
,
755
765
Rosa
F. M.
(
1989
).
Mix.1, a homeobox mRNA inducible by mesoderm inducers, is expressed mostly in the presumptive endodermal cells of Xenopus embryos.
Cell
57
,
965
974
Ruiz i Altaba
A.
,
Jessell
T. M.
(
1992
)
Pintallavis, a gene expressed in the organizer and midline cells of frog embryos: involvement in the development of the neural axis.
Development
116
,
81
93
Ruiz i Altalba
A.
(
1994
)
Pattern formation in the vertebrate neural plate.
Trends in Neurosci
17
,
233
243
Sasai
Y.
,
Lu
B.
,
Steinbesser
H.
,
De Robertis
E. M.
(
1995
)
Regulation of neural induction by the Chd and BMP-4 antagonistic patterning signals in Xenopus.
Nature
376
,
333
336
Sasai
Y.
,
Lu
B.
,
Steinbesser
H.
,
Geissert
D.
,
Gont
L. K.
,
De Robertis
E. M.
(
1994
)
Xenopus chordin: a novel dorsalizing factor activated by Organizer-specific homeobox genes.
Cell
79
,
779
790
Sato
S. M.
,
Sargent
T. D.
(
1991
)
Localized and inducible expression of Xenopus-Posterior (Xpo), a novel gene active in early frog embryos, encoding a protein with a ‘CCHC’ finger domain.
Development
112
,
747
753
Schonemann
M. D.
,
Ryan
A. K.
,
McEvilly
R. J.
,
O'Connell
S. M.
,
Arias
C. A.
,
Kalla
K. A.
,
Li
P.
,
Sawchenko
P. E.
,
Rosenfeld
M. G.
(
1995
)
Develoment and survival of the endocrine hypothalamus and posterior pituitary gland requires the neuronal POU domain factor Brn-2.
Genes Dev
9
,
3122
3135
Siegfried
E.
,
Chou
T.
,
Perrimon
N.
(
1992
)
wingless signaling acts through zeste-white 3, the Drosophila homolog of glycogen synthse kinase-3, to regulate engrailed to establish cell fate.
Cell
71
,
76
80
Shawlot
W.
,
Behringer
R. R.
(
1995
)
Requirement for Lim1 in head-organizer function.
Nature
374
,
425
30
Smith
J. C.
,
Price
B. M. J.
,
Green
J. B. A.
,
Weigel
D.
,
Herrmann
B. G.
(
1991
)
Expression of a Xenopus homolog of Brachyury (T) is an immediate-early response gene to mesoderm induction.
Cell
67
,
70
87
Smith
W. C.
,
Harland
R. M.
(
1991
)
Injected Xwnt-8 RNA acts early in Xenopus embryos to promote formation of a vegetal dorsalizing center.
Cell
67
,
753
765
Smith
W. C.
,
Knecht
A. K.
,
Wu
M.
,
Harland
R. M.
(
1993
)
Secreted noggin protein mimics the Spemann Organizer in dorsalizing Xenopus mesoderm.
Nature
361
,
547
549
Smith
W. C.
,
McKendry
R.
,
Ribisi
S.
Jr
,
Harland
R. M.
(
1995
)
A nodal -related gene defines a physical and functional domain within the Spemann organizer.
Cell
82
,
37
46
Sokol
S.
,
Christian
J. L.
,
Moon
R. T.
,
Melton
D. A.
(
1991
)
Injected Wnt RNA induces a complete body axis in Xenopus embryos.
Cell
67
,
741
751
Steinbesser
H.
,
Fainsod
A.
,
Niehrs
C.
,
Sasai
Y.
,
De Robertis
E. M.
(
1995
)
The role of gsc and BMP-4 in dorsal-ventral patterning of the marginal zone in Xenopus: a loss-of-function study using antisense RNA.
EMBO J
14
,
5230
5243
Taira
M.
,
Jamrich
M.
,
Good
P. J.
,
Dawid
I. B.
(
1992
)
The LIM domain-containing homeo box gene Xlim-1 is expressed specifically in the organizer region of Xenopus gastrula embryos.
Genes Dev
6
,
356
366
Taira
M.
,
Otani
H.
,
Saint-Jeannet
J.-P.
,
Dawid
I. B.
(
1994
)
Role of the LIM class hemeodomain protein Xlim-1 in neural and muscle induction by the Spemann organizer in Xenopus.
Nature
372
,
677
679
Thomsen
G. H.
,
Melton
D. A.
(
1993
)
Processed Vg1 protein is an axial mesoderm inducer in Xenopus.
Cell
74
,
433
441
Turner
D. L.
,
Weintraub
H.
(
1994
)
Expression of achaete-scute homolog 3 in Xenopus embryos converts ectodermal cells to a neural fate.
Genes Dev
8
,
1434
1447
Vodicka
M. A.
,
Gerhart
J. C.
(
1995
)
Blastomere derivation and domains of gene expression in the Spemann organizer of Xenopuslaevis.
Development
121
,
3505
3518
Von Dassow
G.
,
Schmidt
J. E.
,
Kimelman
D.
(
1993
)
Induction of Xenopus organizer: expression and regulation of Xnot, a novel FGF and activin-regulated homeo box gene.
Genes Dev
7
,
355
366
Watabe
T.
,
Kim
S.
,
Condia
A.
,
Rothbacher
U.
,
Hashimoto
C.
,
Inoue
K.
,
Cho
K.
(
1995
)
Molecular mechanisms of Spemann's organizer formation: conserved growth factor synergy between Xenopus and mouse.
Genes Dev
9
,
3038
3050
Weinstein
D. E.
,
Burrola
P. G.
,
Lemke
G.
(
1995
)
Premature schwann cell differentiation and hypermyelination in mice expressing a targeted antagonist of the POU transcription factor SCIP.
Molec. Cell. Neurosci
6
,
212
229
Wilson
P. A.
,
Hemmati-Brivanlou
A.
(
1995
)
Induction of epidermis and inhibition of neural fate by BMP-4.
Nature
376
,
331
333
Witta
S. E.
,
Agarwal
V. R.
,
Sato
S. M.
(
1995
)
XlPOU 2, a noggin-inducible gene, has direct neuralizing activity.
Development
121
,
721
730
Yang
X.
,
Yeo
S.
,
Dick
T.
,
Chia
W.
(
1993
)
The role of a Drosophila POU homeodomain gene in the specification of neural precursor cell identity in the developing central nervous system.
Genes Dev
7
,
504
516
Zaraisky
A. G.
,
Ecochard
V.
,
Kazanskaya
O. V.
,
Lukyanov
S. A.
,
Fesenko
I. V.
,
Duprat
A.-M.
(
1995
)
The homeobox-containing gene Xanf-1 may control development of the Spemann organizer.
Development
121
,
3839
3847
Zimmerman
L. B.
,
De Jesus-Escobar
J. M.
,
Harland
R. M.
(
1996
)
The Spemann organizer signal noggin binds and inactivates bone morphogenetic protein 4.
Cell
86
,
599
606
This content is only available via PDF.