Segmentation of a vertebrate embryo begins with the subdivision of the paraxial mesoderm into somites through a not-well-understood process. Recent studies provided evidence that the Notch-Delta and the FGFR (fibroblast growth factor receptor) signalling pathways are required for segmentation. In addition, the Mesp family of bHLH transcription factors have been implicated in establishing a segmental prepattern in the presomitic mesoderm. In this study, we have characterized zebrafish mesp-a and mesp-b genes that are closely related to Mesp family genes in other vertebrates. During gastrulation, only mesp-a is expressed in the paraxial mesoderm at the blastoderm margin. During the segmentation period, both genes are segmentally expressed in one to three stripes in the anterior parts of somite primordia. In fused somites (fss) embryos, in which all early somite boundary formation is blocked, initial mesp-a expression at the gastrula stage remains intact, but the expression of mesp-a and mesp-b is not detected during the segmentation period. This suggests that these genes are downstream targets of fss at the segmentation stage. Comparison with her1 expression (Muller, M., von Weizsacker, E. and Campos-Ortega, J. A. (1996) Development 122, 2071–2078) suggests that, like her1, mesp genes are not expressed in primordia of the first several somites. Furthermore, we found that zebrafish her1 expression oscillates in the presomitic mesoderm. The her1 stripe, which first appears in the tailbud region, moves in a caudal to rostral direction, and it finally overlaps the most rostral mesp stripe. Thus, in the trunk region, both her1 and mesp transcripts are detected in every somite primordium posterior to the forming somites. Ectopic expression of Mesp-b in embryos causes a loss of the posterior identity within the somite primordium, leading to a segmentation defect. These embryos show a reduction in expression of the posterior genes, myoD and notch5, with uniform expression of the anterior genes, FGFR1, papc and notch6. These observations suggest that zebrafish mesp genes are involved in anteroposterior specification within the presumptive somites, by regulating the essential signalling pathways mediated by Notch-Delta and FGFR.
REFERENCES
REFERENCES
Amacher
S. L.
, Kimmel
C. B.
(1998
) Promoting notochord fate and repressing muscle development in zebrafish axial mesoderm.
Development
125
, 1397
–1406
Aoyama
H.
, Asamoto
K.
(1988
) Determination of somite cells: independence of cell differentiation and morphogenesis.
Development
104
, 15
–28
Aulehla
A.
, Johnson
R. L.
(1999
) Dynamic expression of lunatic fringe suggests a link between notch signaling and an autonomous cellular oscillator driving somitic segmentation.
Dev. Biol
207
, 49
–61
del Barco Barrantes
I.
, Elia
A. J.
, Wunsch
K.
, Hrabe De Angelis
M.
, Mak
T. W.
, Rossant
J.
, Conlon
R. A.
, Grossler
A.
, de la Pompa
J. L.
(1999
) Interaction between Notch singalling and Lunatic fringe during somite boundary formation in the mouse.
Curr. Biol
9
, 470
–480
Blader
P.
, Fischer
N.
, Gradwohl
G.
, Guillemont
F.
, Strähle
U.
(1997
) The activity of Neurogenin1 is controlled by local cues in the zebrafish embryo.
Development
124
, 4557
–4569
Buchberger
A.
, Seidl
K.
, Klein
C.
, Eberhardt
H.
, Arnold
H. H.
(1998
) cMeso-1, a novel bHLH transcription factor, is involved in somite formation in chicken embryos.
Dev. Biol
199
, 201
–215
Chomczynski
P.
, Sacchi
N.
(1987
) Single-step method of RNA isolation by acid guanidinium thiocyanate-phenol-chloroform extraction.
Analyt. Biochem
162
, 156
–159
Conlon
R. A.
, Reaume
A. G.
, Rossant
J.
(1995
) Notch1 is required for the coordinate segmentation of somites.
Development
121
, 1533
–1545
Cooke
J.
(1978
) Somite abnormalities caused by short heat shocks to pre-neurula stages of Xenopuslaevis.
J. Embryol. Exp. Morphol
45
, 283
–294
Currie
P. D.
, Ingham
P. W.
(1998
) The generation and interpretation of positional information within the vertebrate myotome.
Mech. Dev
73
, 3
–21
Deng
C. X.
, Wynshaw-Boris
A.
, Shen
M. M.
, Daugherty
C.
, Ornitz
D. M.
, Leder
P.
(1994
) Murine FGFR-1 is required for early postimplantation growth and axial organization.
Genes Dev
8
, 3045
–3057
Durbin
L.
, Brennan
C.
, Shiomi
K.
, Cooke
J.
, Barrios
A.
, Shanmugalingam
S.
, Guthrie
B.
, Lindberg
R.
, Holder
N.
(1998
) Eph signaling is required for segmentation and differentiation of the somites.
Genes Dev
12
, 3096
–3109
Elsdale
T.
, Pearson
M.
, Whitehead
M.
(1976
) Abnormalities in somite segmentation following heat shock to Xenopus embryos.
J. Embryol. Exp. Morphol
35
, 625
–635
Evrard
Y.
, Lun
Y.
, Aulehla
A.
, Gan
L.
, Johnson
R. L.
(1998
) Lunatic fringe is an essential mediator of somite segmentation and patterning.
Nature
394
, 377
–381
Forsberg
H.
, Crozet
F.
, Brown
N. A.
(1998
) Waves of mouse Lunatic fringe expression, in four-hour cycles at two-hour interavals, precede somite boundary formation.
Curr. Biol
8
, 1027
–1030
Gilland
E.
, Baker
R.
(1993
) Conservation of neuroepithelial and mesodermal segments in the embryonic vertebrate head.
Acta Anat
148
, 110
–123
Halpern
M. E.
, Hatta
K.
, Amacher
S. L.
, Talbot
W. S.
, Yan
Y. L.
, Thisse
B.
, Thisse
C.
, Postlethwait
J. H.
, Kimmel
C. B.
(1997
) Genetic interactions in zebrafish midline development.
Dev. Biol
187
, 154
–170
Holland
L. Z.
, Kene
M.
, Williams
N. A.
, Holland
N. D.
(1997
) Sequence and embryonic expression of the amphioxus engrailed gene (AmphiEn): the metameric pattern of transcription resembles that of its segment-polarity homolog in Drosophila.
Development
124
, 1723
–1732
Hrabe de Angelis
M.
, McIntyre
J.
II, Gossler
A.
(1997
) Maintenance of somite borders in mice requires the Delta homologue DII1.
Nature
386
, 717
–721
Jen
W.-C.
, Gawantka
V.
, Pollet
N.
, Niehrs
C.
, Kintner
C.
(1999
) Periodic repression of Notch pathway genes governs the segmentation of Xenopus embryos.
Genes Dev
13
, 1486
–1499
Jen
W. C.
, Wettstein
D.
, Turner
D.
, Chitnis
A.
, Kintner
C.
(1997
) The Notch ligand, X-Delta-2, mediates segmentation of the paraxial mesoderm in Xenopus embryos.
Development
124
, 1169
–1178
Jiang
Y. J.
, Smithers
L.
, Lewis
J.
(1998
) The clock is linked to notch signalling.
Curr. Biol
8
, 868
–871
Joseph
E. M.
, Cassetta
L. A.
(1999
) Mespo: a novel basic helix-loop-helix gene expressed in the presomitic mesoderm and posterior tailbud of Xenopus embryo.
Mech. Dev
82
, 191
–194
Jowett
T.
, Yan
Y.-L.
(1996
) Double fluorescent in situ hybridization to zebrafish embryo.
Trends Genet
12
, 387
–389
Keynes
R. J.
, Stern
C. D.
(1984
) Segmentation in the vertebrate nervous system.
Nature
310
, 786
–9
Keynes
R. J.
, Stern
C. D.
(1988
) Mechanisms of vertebrate segmentation.
Development
103
, 413
–429
Kimmel
C. B.
, Ballard
W. W.
, Kimmel
S. R.
, Ullmann
B.
, Schilling
T. F.
(1995
) Stages of embryonic development of the zebrafish.
Dev. Dyn
203
, 253
–310
Kimmel
C. B.
, Sepich
D. S.
, Trevarrow
B.
(1988
) Development of segmentation in zebrafish.
Development
104
, 197
–207
Korzh
V.
, Sleptsova
I.
, Liao
J.
, He
J.
, Gong
Z.
(1998
) Expression of zebrafish bHLH genes ngn1 and nrd defines distinct stages of neural differentiation.
Dev. Dyn
213
, 92
–104
Koshida
S.
, Shinya
M.
, Mizuno
T.
, Kuroiwa
A.
, Takeda
H.
(1998
) Initial anteroposterior pattern of the zebrafish central nervous system is determined by differential competence of the epiblast.
Development
125
, 1957
–1966
Kozak
M.
(1987
) An analysis of 5-noncoding sequences from 699 vertebrate messenger RNAs.
Nucl. Acids Res
15
, 8125
–8148
McGrew
M. J.
, Dale
J. K.
, Fraboulet
S.
, Pourquie
O.
(1998
) The lunatic fringe gene is a target of the molecular clock linked to somite segmentation in avian embryos.
Curr. Biol
8
, 979
–982
Makita
R.
, Mizuno
T.
, Koshida
S.
, Kuroiwa
A.
, Takeda
H.
(1998
) Zebrafish wnt11: pattern and regulation of the expression by the yolk cell and No tail activity.
Mech. Dev
71
, 165
–176
Muller
M.
, von Weizsäcker
E.
, Campos-Ortega
J. A.
(1996
) Expression domains of a zebrafish homologue of the Drosophila pair-rule gene hairy correspond to primordia of alternating somites.
Development
122
, 2071
–2078
Oka
C.
, Nakano
T.
, Wakeham
A.
, de la Pompa
J. L.
, Mori
C.
, Sakai
T.
, Okazaki
S.
, Kawaichi
M.
, Shiota
K.
, Mak
T. W.
, Honjo
T.
(1995
) Disruption of the mouse RBP-J kappa gene results in early embryonic death.
Development
121
, 3291
–301
Orr-Urtreger
A.
, Givol
D.
, Yayon
A.
, Yarden
Y.
, Lonai
P.
(1991
) Developmental expression of two murine fibroblast growth factor receptors, flg and bek.
Development
113
, 1419
–1434
Primmett
D. R.
, Stern
C. D.
, Keynes
R. J.
(1988
) Heat shock causes repeated segmental anomalies in the chick embryo.
Development
104
, 331
–339
Palmeirim
I.
, Henrique
D.
, Ish-Horowicz
D.
, Pourquie
O.
(1997
) Avian hairy gene expression identifies a molecular clock linked to vertebrate segmentation and somitogenesis.
Cell
91
, 639
–648
Roy
M. N.
, Prince
V. E.
, Ho
R. K.
(1999
) Heat shock produces periodic somitic disturbances in the zebrafish embryo.
Mech. Dev
85
, 27
–34
Saga
Y.
(1998
) Genetic rescue of segmentation defect in MesP2-deficient mice by MesP1 gene replacement.
Mech. Dev
75
, 53
–66
Saga
Y.
, Hata
N.
, Kobayashi
S.
, Magnuson
T.
, Seldin
M. F.
, Taketo
M. M.
(1996
) MesP1: a novel basic helix-loop-helix protein expressed in the nascent mesodermal cells during mouse gastrulation.
Development
122
, 2769
–2778
Saga
Y.
, Hata
N.
, Koseki
H.
, Taketo
M. M.
(1997
) Mesp2: a novel mouse gene expressed in the presegmented mesoderm and essential for segmentation initiation.
Genes Dev
11
, 1827
–1839
Saitou
N.
, Nei
M.
(1987
) The neighbor-joining method: a new method for reconstructing phylogenetic trees.
Mol. Biol. Evol
4
, 406
–425
Sparrow
D. B.
, Jen
W. C.
, Kotecha
S.
, Towers
N.
, Kintner
C.
, Mohun
T. J.
(1998
) Thylacine 1 is expressed segmentally within the paraxial mesoderm of the Xenopus embryo and interacts with the Notch pathway.
Development
125
, 2041
–2051
Stachel
S. E.
, Grunwald
D. J.
, Myers
P. Z.
(1993
) Lithium perturbation and goosecoid expression identify a dorsal specification pathway in the pregastrula zebrafish.
Development
117
, 1261
–1274
Stern
C. D.
, Keynes
R. J.
(1987
) Interactions between somite cells: the formation and maintenance of segment boundaries in the chick embryo.
Development
99
, 261
–272
Talbot
W. S.
, Trevarrow
B.
, Halpern
M. E.
, Melby
A. E.
, Farr
G.
, Postlethwait
J. H.
, Jowett
T.
, Kimmel
C. B.
, Kimelman
D.
(1995
) A homeobox gene essential for zebrafish notochord development.
Nature
378
, 150
–157
Takada
S.
, Stark
K. L.
, Vassileva
G.
, McMahon
J. A.
(1994
) Wnt-3a regulates somite and taibud formation in the mouse embryo.
Gene Dev
8
, 174
–189
van Eeden
F. J.
, Granato
M.
, Schach
U.
, Brand
M.
, Furutani-Seiki
M.
, Haffter
P.
, Hammerschmidt
M.
, Heisenberg
C. P.
, Jiang
Y. J.
, Kane
D. A.
, Kelsh
R. N.
, Mullins
M. C.
, Odenthal
J.
, Warga
R. M.
, Allende
M. L.
, Weinberg
E. S.
, Nusslein-Volhard
C.
(1996
) Mutations affecting somite formation and patterning in the zebrafish, Danio rerio.
Development
123
, 153
–164
van Eeden
F. J.
, Holley
S. A.
, Haffter
P.
, Nusslein-Volhard
C.
(1998
) Zebrafish segmentation and pair-rule patterning.
Dev. Genet
23
, 65
–76
Weinberg
E. S.
, Allende
M. L.
, Kelly
C. S.
, Abdelhamid
A.
, Murakami
T.
, Andermann
P.
, Doerre
O. G.
, Grunwald
D. J.
, Riggleman
B.
(1996
) Developmental regulation of zebrafish MyoD in wild-type, no tail and spadetail embryos.
Development
122
, 271
–280
Yamaguchi
T. P.
, Conlon
R. A.
, Rossant
J.
(1992
) Expression of the fibroblast growth factor receptor FGFR-1/flg during gastrulation and segmentation in the mouse embryo.
Dev. Biol
152
, 75
–88
Yamaguchi
T. P.
, Harpal
K.
, Henkemeyer
M.
, Rossant
J.
(1994
) fgfr-1 is required for embryonic growth and mesodermal patterning during mouse gastrulation.
Genes Dev
8
, 3032
–3044
Yamamoto
A.
, Amacher
S. L.
, Kim
S. H.
, Geissert
D.
, Kimmel
C. B.
, De Robertis
E. M.
(1998
) Zebrafish paraxial protocadherin is a downstream target of spadetail involved in morphogenesis of gastrula mesoderm.
Development
125
, 3389
–97
Zhang
N.
, Gridley
T.
(1998
) Defects in somite formation in lunatic fringe -deficient mice.
Nature
394
, 374
–377
This content is only available via PDF.
© 2000 by Company of Biologists
2000
