The Xenopus nodal related-1 (Xnr1) gene has a complex expression pattern in embryos, with two temporal phases. In the first phase, transcripts are first detected in perinuclear sites in the vegetal region of the blastula. During gastrulation, this expression disappears and transcripts become localised to the dorsal marginal zone. Expression stops and then restarts in a second phase at neurula and tailbud stages, firstly in two symmetric patches near the posterior end of the notochord, and then asymmetrically in a large domain in the left lateral plate mesoderm. In this study, we have investigated the regulation of the early phase of expression of Xnr1. We show that the T-box transcription factor VegT can induce Xnr1. It had previously been shown that Xnr1 can induce VegT in ectoderm cells and we show that the early expression of Xnr1 is regulated by an autoregulatory loop. By inspection of the Xnr1 promoter sequence, we have identified two non-palindromic T-box-binding sites, which are 10 bp apart. Using mutational analysis, we have shown that these elements are required for the VegT induction of Xnr1. The Xnr1 promoter shows striking homologies with the Xnr3 promoter. In particular, two elements that are required for Wnt signaling are conserved between these two promoters, but the two T-box sites are not conserved, and Xnr3 is not induced by VegT. A region of the promoter containing the T-box sites and the Wnt sites is sufficient to drive expression of a reporter gene in a dorsal domain in transgenic Xenopus at the gastrula stage. We show that this pattern of expression of the transgene in gastrulae is not dependent on the T-box sites.

REFERENCES

REFERENCES
Adachi
H.
,
Saijoh
Y.
,
Mochida
K.
,
Ohishi
S.
,
Hashiguchi
H.
,
Hirao
A.
,
Hamada
H.
(
1999
)
Determination of left/right asymmetric expression of nodal by a left side-specific enhancer with sequence similarity to a lefty-2 enhancer.
Genes Dev
13
,
1589
1600
Barnett
M. W.
,
Old
R. W.
,
Jones
E. A.
(
1998
)
Neural induction and patterning by fibroblast growth factor, notochord and somite tissue in Xenopus.
Develop. Growth Differ
40
,
47
57
Bouwmeester
T.
,
Kim
S.-H.
,
Sasai
Y.
,
Lu
B.
,
De Robertis
E. M.
(
1996
)
Cerberus is a head-inducing secreted factor expressed in the anterior endoderm of Spemann's organizer.
Nature
382
,
595
601
Carreira
S.
,
Dexter
T. J.
,
Yavuzer
U.
,
Easty
D. J.
,
Goding
C. R.
(
1998
)
Brachyury-related transcription factor Tbx2 and repression of the melanocyte-specific TRP-1 promoter.
Mol. Cell Biol
18
,
5099
5108
Casey
E. S.
,
O'Reilly
M.-A. J.
,
Conlon
F. L.
,
Smith
J. C.
(
1998
)
The T-box transciption factor Brachyury regulates expression of eFGF through binding to a non-palindromic response element.
Development
125
,
3887
3894
Casey
E. S.
,
Tada
M.
,
Faiclough
L.
,
Wylie
C. C.
,
Heasman
J.
,
Smith
J. C.
(
1999
)
Bix4 is directly activated by VegT and mediates endoderm formation in Xenopus development.
Development
126
,
4193
4200
Christian
J. L.
,
McMahon
J. A.
,
McMahon
A. P.
,
Moon
R. T.
(
1991
)
Xwnt8, a Xenopus Wnt-1/int-1 related gene responsive to mesoderm inducing growth factors, may play a role in ventral mesoderm patterning during embryogenesis.
Development
111
,
1045
1055
Clements
D.
,
Friday
R. V.
,
Woodland
H. R.
(
1999
)
Mode of action of VegT in mesoderm and endoderm formation.
Development
126
,
4903
4911
Collignon
J.
,
Varlet
I.
,
Robertson
E. J.
(
1996
)
Relationship between asymmetric nodal expression and the direction of embryonic turning.
Nature
381
,
155
158
Cook
J. P.
,
Savage
P. M.
,
Lord
J. M.
,
Roberts
L. M.
(
1993
)
Biologically active interleukin 2-ricin-A chain fusion proteins may require intracellular proteolytic cleavage to exhibit a cytotoxic effect.
Bioconj. Chem
4
,
440
447
Darras
S.
,
Marikawa
Y.P.
,
Elinson
R.
,
Lemaire
P.
(
1997
)
Animal and vegetal pole cells of early Xenopus embryos respond differently to maternal dorsal determinants: implications for the patterning of the organiser.
Development
124
,
4275
4286
Ecochard
V.
,
Cayrol
C.
,
Rey
S.
,
Foulquier
F.
,
Caillol
D.
,
Lemaire
P.
,
Duprat
A. M.
(
1998
)
A novel XenopusMi x-like gene milk involved in the control of endomesodermal fates.
Development
125
,
2577
2585
Henry
G. L.
,
Brivanlou
I. H.
,
Kessler
D. S.
,
Hemmati-Brivanlou
A.
,
Melton
D. A.
(
1996
)
TGF-signals and a prepattern in Xenopus laevis endodermal development.
Development
122
,
1007
1015
Henry
G. L.
,
Melton
D. A.
(
1998
)
Mixer, a homeobox gene required for endoderm development.
Science
281
,
91
96
Horb
M. E.
,
Thomsen
G. H.
(
1997
)
A vegetally localized T-box transcription factor in Xenopus eggs specifies mesoderm and endoderm and is essential for embryonic mesoderm formation.
Development
124
,
1689
1698
Hudson
C.
,
Clements
D.
,
Friday
R. V.
,
Stott
D.
,
Woodland
H. R.
(
1997
)
Xsox17and- mediate endoderm formation in Xenopus.
Cell
91
,
397
405
Isaacs
H. V.
,
Pownall
M. E.
,
Slack
J. M.
(
1994
)
eFGF regulates Xbra expression during Xenopus gastrulation.
EMBO J
13
,
4469
4481
Jones
C. M.
,
Kuehn
M. R.
,
Hogan
B. L. M.
,
Smith
J. C.
,
Wright
C. V. E.
(
1995
)
Nodal-related signals induce axial mesoderm and dorsalize mesoderm during gastrulation.
Development
121
,
3651
3662
Jones
C. M.
,
Armes
N.
,
Smith
J. C.
(
1996
)
Signalling by TGF-family members: short-range effects of Xnr-2 and BMP-4 contrast with the long-range effects of activin.
Curr. Biol
6
,
1468
1475
Joseph
E. M.
,
Melton
D. A.
(
1997
)
Xnr4: a Xenopus nodal-related gene expressed in the Spemann organizer.
Dev. Biol
184
,
367
372
Joseph
E. M.
,
Melton
D. A.
(
1998
)
Mutant Vg1 ligands disrupt endoderm and mesoderm formation in Xenopus embryos.
Development
125
,
2677
2685
Kispert
A.
,
Herrmann
B. G.
(
1993
)
The Brachyury gene encodes a novel DNA binding protein.
EMBO J
12
,
3211
3220
Kofron
M.
,
Demel
T.
,
Xanthos
J.
,
Lohr
J.
,
Sun
B.
,
Sive
H.
,
Osada
S.-I.
,
Wright
C.
,
Wylie
C.
,
Heasman
J.
(
1999
)
Mesoderm induction in Xenopus is a zygotic event regulated by maternal VegT via TGFgrowth factors.
Development
126
,
5759
5770
Kroll
K. L.
,
Amaya
E.
(
1996
)
Transgenic Xenopus embryos from sperm nuclear transplantations reveal FGF signaling requirements during gastrulation.
Development
122
,
3173
3183
Larabell
C. A.
,
Torres
M.
,
Rowning
B. A.
,
Yost
C.
,
Miller
J. R.
,
Wu
M.
,
Kimelman
D.
,
Moon
R. T.
(
1997
)
Establishment of the dorso-ventral axis in Xenopus embryos is presaged by early asymmetries in-catenin that are modulated by the Wnt signaling pathway.
J. Cell Biol
136
,
1123
1136
Lemaire
P.
,
Darras
S.
,
Caillol
D.
,
Kodjabachian
L.
(
1998
).
A role for the vegetally expressed Xenopus gene Mix.1 in endoderm formation and in the restriction of mesoderm to the marginal zone.
Development
125
,
2371
2380
Levin
M.
,
Johnson
R. L.
,
Stern
C. D.
,
Kuehn
M.
,
Tabin
C.
(
1995
)
A molecular pathway determining left-right asymmetry in chick embryogenesis.
Cell
82
,
803
814
Lustig
K. D.
,
Kroll
K.
,
Sun
E.
,
Ramos
R.
,
Elmendorf
H.
,
Kirschner
M. W.
(
1996
)
A Xenopus nodal-related gene that acts in synergy with noggin to induce complete secondary axis and notochord formation.
Development
122
,
3275
3282
Lustig
K. D.
,
Kroll
K. L.
,
Sun
E. E.
,
Kirschner
M. W.
(
1996
)
Expression cloning of a Xenopus T-related gene (Xombi) involved in mesodermal patterning and blastopore lip formation.
Development
122
,
4001
4012
McKendry
R.
,
Hsu
S.-C.
,
Harland
R. M.
,
Grosschedl
R.
(
1997
)
LEF1/TCF proteins mediate wnt-inducible transcription from the Xenopus nodal-related-3promoter.
Dev. Biol
192
,
420
431
Muller
C. W.
,
Herrmann
B. G.
(
1997
)
Crystallographic structure of the T domain-DNA complex of the Brachyury transcription factor.
Nature
389
,
884
888
Newman
C. S.
,
Chia
F.
,
Krieg
P. A.
(
1997
)
The Xhex homeobox gene is expressed during development of the vascular endothelium: overexpression leads to an increase in vascular endothelial cell number.
Mech. Dev
66
,
88
93
Norris
D. P.
,
Robertson
E. J.
(
1999
)
Asymmetric and node-specific nodal expression patterns are controlled by two cis -acting regulatory elements.
Genes Dev
13
,
1575
1588
Osada
S.-I.
,
Wright
C. V. E.
(
1999
)
Xenopus nodal -related signaling is essential for mesendodermal patterning during early embryogenesis.
Development
126
,
3229
3240
Piccolo
S.
,
Agius
E.
,
Leyns
L.
,
Bhattacharyya
S.
,
Grunz
H.
,
Bouwmeester
T.
,
De Robertis
E. M.
(
1999
)
Thehead inducer Cerberus is a multifunctional antagonist of Nodal, BMP and Wnt signals.
Nature
397
,
707
710
Ramsdell
A. F.
,
Yost
H. J.
(
1998
)
Molecular mechanisms of vertebrate left-right development.
Trends Genet
14
,
459
465
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
Ryan
K.
,
Garrett
N.
,
Mitchell
A.
,
Gurdon
J. B.
(
1996
)
Eomesodermin, a key early gene in Xenopus mesoderm differentiation.
Cell
87
,
989
1000
Sampath
K.
,
Cheng
A. M. S.
,
Frisch
A.
,
Wright
C. V. E.
(
1997
)
Functional differences among Xenopus nodal-related genes in left-right axis determination.
Development
124
,
3293
3302
Schulte-Merker
S.
,
Smith
J. C.
(
1995
)
Mesoderm formation in response to Brachyury requires FGF signalling.
Curr. Biol
5
,
62
67
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 to mesoderm induction.
Cell
67
,
79
87
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
Stennard
F.
,
Carnac
G.
,
Gurdon
J. B.
(
1996
)
The Xenopus T-box gene, Antipodean, encodes a vegetally localised maternal mRNA and can trigger mesoderm formation.
Development
122
,
4179
4188
Tada
M.
,
Casey
E. S.
,
Fairclough
L.
,
Smith
J. C.
(
1998
)
Bix1, a direct target of Xenopus T-box genes, causes formation of ventral mesoderm and endoderm.
Development
125
,
3997
4006
Vodicka
M. A.
,
Gerhart
J. C.
(
1995
)
Blastomere derivation and domains of gene expression in the Spemann organizer of Xenopus laevis.
Development
121
,
3505
3518
Yasuo
H.
,
Lemaire
P.
(
1999
)
A two-step model for the fate of presumptive endodermal blastomeres in Xenopus embryos.
Current Biol
9
,
869
879
Zakany
J.
,
Tuggle
C. K.
,
Patel
M. D.
,
Nguyen-Huu
M. C.
(
1988
)
Spatial regulation of homeobox gene fusions in the embryonic central nervous system of transgenic mice.
Neuron
1
,
679
691
Zhang
J.
,
King
M. L.
(
1996
)
Xenopus VegT RNA is localized to the vegetal cortex during oogenesis and encodes a novel T-box transcription factor involved in mesodermal patterning.
Development
122
,
4119
4129
Zhang
J.
,
Houston
D. W.
,
King
M. L.
,
Payne
C.
,
Wylie
C.
,
Heasman
J.
(
1998
)
The role of maternal VegT in establishing the primary germ layers in Xenopus embryos.
Cell
94
,
515
524
Zorn
A. M.
,
Butler
K.
,
Gurdon
J. B.
(
1999
)
Anterior endomesoderm specification in Xenopus by Wnt/-catenin and TGF- signalling pathways.
Dev. Biol
209
,
282
297
This content is only available via PDF.