Sonic hedgehog (Shh), produced by the notochord and floor plate, is proposed to function as an inductive and trophic signal that controls somite and neural tube patterning and differentiation. To investigate Shh functions during somite myogenesis in the mouse embryo, we have analyzed the expression of the myogenic determination genes, Myf5 and MyoD, and other regulatory genes in somites of Shh null embryos and in explants of presomitic mesoderm from wild-type and Myf5 null embryos. Our findings establish that Shh has an essential inductive function in the early activation of the myogenic determination genes, Myf5 and MyoD, in the epaxial somite cells that give rise to the progenitors of the deep back muscles. Shh is not required for the activation of Myf5 and MyoD at any of the other sites of myogenesis in the mouse embryo, including the hypaxial dermomyotomal cells that give rise to the abdominal and body wall muscles, or the myogenic progenitor cells that form the limb and head muscles. Shh also functions in somites to establish and maintain the medio-lateral boundaries of epaxial and hypaxial gene expression. Myf5, and not MyoD, is the target of Shh signaling in the epaxial dermomyotome, as MyoD activation by recombinant Shh protein in presomitic mesoderm explants is defective in Myf5 null embryos. In further support of the inductive function of Shh in epaxial myogenesis, we show that Shh is not essential for the survival or the proliferation of epaxial myogenic progenitors. However, Shh is required specifically for the survival of sclerotomal cells in the ventral somite as well as for the survival of ventral and dorsal neural tube cells. We conclude, therefore, that Shh has multiple functions in the somite, including inductive functions in the activation of Myf5, leading to the determination of epaxial dermomyotomal cells to myogenesis, as well as trophic functions in the maintenance of cell survival in the sclerotome and adjacent neural tube.
Reference
Amthor
H.
, Christ
B.
, Patel
K.
(1999
) A molecular mechanism enabling continuous embryonic muscle growth—a balance between proliferation and differentiation.
Development
126
, 1041
–1053
Asakura
A.
, Tapscott
S. J.
(1998
) Apoptosis of epaxial myotome in Danforth's short-tail (Sd) mice in somites that form following notochord degeneration.
Dev. Biol
203
, 276
–289
Blagden
C. S.
, Currie
P. D.
, Ingham
P. W.
, Hughes
S. M.
(1997
) Notochord induction of zebrafish slow muscle mediated by Sonic hedgehog.
Genes Dev
11
, 2163
–2175
Borycki
A.-G.
, Mendham
L.
, Emerson
C. P.
Jr (1998
) Control of somite patterning by Sonic hedgehog and its downstream signal response genes.
Development
125
, 777
–790
Borycki
A. G.
, Li
J.
, Jin
F.
, Emerson
C. P.
, Epstein
J.
(1999
) Pax3 functions in cell survival and in Pax7 regulation.
Development
126
, 1665
–1674
Braun
T.
, Bober
E.
, Rudnicki
M. A.
, Jaenisch
R.
, Arnold
H. H.
(1994
) MyoD expression marks the onset of skeletal myogenesis in Myf-5 mutant mice.
Development
120
, 3083
–3092
Buckingham
M.
(1992
) Making muscle in mammals.
Trends Genet
8
, 144
–148
Chiang
C.
, Litingtung
Y.
, Lee
E.
, Young
K. E.
, Corden
J. L.
, Westphal
H.
, Beachy
P. A.
(1996
) Cyclopia and defective axial patterning in mice lacking sonic hedgehog gene function.
Nature
383
, 407
–413
Cossu
G.
, Kelly
R.
, Tajbakhsh
S.
, Di Donna
S.
, Vivarelli
E.
, Buckingham
M.
(1996
) Activation of different myogenic pathways: myf-5 is induced by the neural tube and MyoD by the dorsal ectoderm in mouse paraxial mesoderm.
Development
122
, 429
–437
Dietrich
S.
, Schubert
F. R.
, Lumsden
A.
(1997
) Control of dorsoventral pattern in the chick paraxial mesoderm.
Development
124
, 3895
–3908
Ding
Q.
, Motoyama
J.
, Gasca
S.
, Mo
R.
, Sasaki
H.
, Rossant
J.
, Hui
C. C.
(1998
) Diminished Sonic hedgehog signaling and lack of floor plate differentiation in Gli2 mutant mice.
Development
125
, 2533
–2543
Duprez
D.
, Fournier-Thibault
C.
, Le Douarin
N.
(1998
) Sonic Hedgehog induces proliferation of committed skeletal muscle cells in the chick limb.
Development
125
, 495
–505
Ericson
J.
, Morton
S.
, Kawakami
A.
, Roelink
H.
, Jessell
T. M.
(1996
) Two critical periods of Sonic Hedgehog signaling required for the specification of motor neuron identity.
Cell
87
, 661
–673
Fan
C. M.
, Kuwana
E.
, Bulfone
A.
, Fletcher
C. F.
, Copeland
N. G.
, Jenkins
N. A.
, Crews
S.
, Martinez
S.
, Puelles
L.
, Rubenstein
J. L.
, Tessier-Lavigne
M.
(1996
) Expression patterns of two murine homologs of Drosophila single-minded suggest possible roles in embryonic patterning and in the pathogenesis of Down syndrome.
Mol. Cell. Neurosc
7
, 1
–16
Fan
C. M.
, Porter
J. A.
, Chiang
C.
, Chang
D. T.
, Beachy
P. A.
, Tessier-Lavigne
M.
(1995
) Long-range sclerotome induction by sonic hedgehog: direct role of the amino-terminal cleavage product and modulation by the cyclic AMP signaling pathway.
Cell
81
, 457
–465
Fan
C. M.
, Tessier-Lavigne
M.
(1994
) Patterning of mammalian somites by surface ectoderm and notochord: evidence for sclerotome induction by a hedgehog homolog.
Cell
79
, 1175
–1186
Fontaine-Perus
J. C.
, Chanconie
M.
, Le Douarin
N. M.
, Gershon
M. D.
, Rothman
T. P.
(1989
) Mitogenic effect of muscle on the neuroepithelium of the developing spinal cord.
Development
107
, 413
–422
Goldhamer
D. J.
, Faerman
A.
, Shani
M.
, Emerson
C. P.
Jr (1992
) Regulatory elements that control the lineage-specific expression of myoD.
Science
256
, 538
–542
Goodrich
L. V.
, Milenkovic
L.
, Higgins
K. M.
, Scott
M. P.
(1997
) Altered neural cell fates and medulloblastoma in mouse patched mutants.
Science
277
, 1109
–1113
Goulding
M. D.
, Chalepakis
G.
, Deutsch
U.
, Erselius
J. R.
, Gruss
P.
(1991
) Pax-3, a novel murine DNA binding protein expressed during early neurogenesis.
EMBO J
10
, 1135
–47
Goulding
M. D.
, Lumsden
A.
, Gruss
P.
(1993
) Signals from the notochord and floor plate regulate the region-specific expression of two Pax genes in the developing spinal cord.
Development
117
, 1001
–1016
Goulding
M. D.
, Lumsden
A.
, Paquette
A. J.
(1994
) Regulation of Pax-3 expression in the dermomyotome and its role in muscle development.
Development
120
, 957
–971
Hahn
H.
, Wojnowski
L.
, Zimmer
A. M.
, Hall
J.
, Miller
G.
, Zimmer
A.
(1998
) Rhabdomyosarcomas and radiation hypersensitivity in a mouse model of Gorlin syndrome [see comments].
Nat. Med
4
, 619
–622
Henrique
D.
, Adam
J.
, Myat
A.
, Chitnis
A.
, Lewis
J.
, Ish-Horowicz
D.
(1995
) Expression of a Delta homologue in prospective neurons in the chick.
Nature
375
, 787
–790
Hirsinger
E.
, Duprez
D.
, Jouve
C.
, Malapert
P.
, Cooke
J.
, Pourquie
O.
(1997
) Noggin acts downstream of Wnt and Sonic Hedgehog to antagonize BMP4 in avian somite patterning.
Development
124
, 4605
–4614
i Altaba
A. R.
(1998
) Combinatorial Gli gene function in floor plate and neuronal inductions by Sonic hedgehog.
Development
125
, 2203
–12
Ikeya
M.
, Takada
S.
(1998
) Wnt signaling from the dorsal neural tube is required for the formation of the medial dermomyotome.
Development
125
, 4969
–4976
Johnson
R. L.
, Laufer
E.
, Riddle
R. D.
, Tabin
C.
(1994
) Ectopic expression of Sonic hedgehog alters dorsal-ventral patterning of somites.
Cell
79
, 1165
–1173
Le Douarin
N. M.
, Teillet
M. A.
, Catala
M.
(1998
) Neurulation in amniote vertebrates: a novel view deduced from the use of quail-chick chimeras.
Int J Dev Biol
42
, 909
–916
Marcelle
C.
, Stark
M. R.
, Bronner-Fraser
M.
(1997
) Coordinate actions of BMPs, Shh and Noggin mediate patterning of the dorsal somite.
Development
124
, 3955
–3963
Maroto
M.
, Reshef
R.
, Munsterberg
A. E.
, Koester
S.
, Goulding
M.
, Lassar
A. B.
(1997
) Ectopic Pax-3 activates MyoD and Myf-5 expression in embryonic mesoderm and neural tissue.
Cell
89
, 139
–148
Matise
M. A.
, Epstein
D. J.
, Park
H. L.
, Platt
K. A.
, Joyner
A. L.
(1998
) Gli2 is required for induction of floor plate and adjacent cells, but not most ventral neurons in the mouse central nervous system.
Development
125
, 2759
–2770
Munsterberg
A. E.
, Kitajewski
J.
, Bumcrot
D. A.
, McMahon
A. P.
, Lassar
A. B.
(1995
) Combinatorial signaling by sonic hedgehog and wnt family members induces myogenic bHLH gene expression in the somite.
Genes Dev
9
, 2911
–2922
Ott
M. O.
, Bober
E.
, Lyons
G.
, Arnold
H.
, Buckingham
M.
(1991
) Early expression of the myogenic regulatory gene, myf-5, in precursor cells of skeletal muscle in the mouse embryo.
Development
111
, 1097
–1107
Pituello
F.
, Medevielle
F.
, Foulquier
F.
, Duprat
A. M.
(1999
) Activation of Pax6 depends on somitogenesis in the chick embryo cervical spinal cord.
Development
126
, 587
–596
Pourquie
O.
, Fan
C. M.
, Coltey
M.
, Hirsinger
E.
, Watanabe
Y.
, Breant
C.
, Francis-West
P.
, Brickell
P.
, Tessier-Lavigne
M.
, Le Douarin
N. M.
(1996
) Lateral and axial signals involved in avian somite patterning: a role for BMP4.
Cell
84
, 461
–471
Roelink
H.
, Augsburger
A.
, Heemskerk
J.
, Korzh
V.
, Norlin
S.
, Ruiz i Altaba
A.
, Tanabe
Y.
, Placzek
M.
, Edlund
T.
, Jessell
T. M.
(1994
) Floor plate and motor neuron induction by vhh-1, a vertebrate homolog of hedgehog expressed by the notochord.
Cell
76
, 761
–775
Rudnicki
M. A.
, Braun
T.
, Hinuma
S.
, Jaenisch
R.
(1992
) Inactivation of MyoD in mice leads to up-regulation of the myogenic HLH gene Myf-5 and results in apparently normal muscle development.
Cell
71
, 383
–390
Rudnicki
M. A.
, Schnegelsberg
P. N.
, Stead
R. H.
, Braun
T.
, Arnold
H. H.
, Jaenisch
R.
(1993
) MyoD or Myf-5 is required for the formation of skeletal muscle.
Cell
75
, 1351
–1359
Sassoon
D.
, Lyons
G.
, Wright
W. E.
, Lin
V.
, Lassar
A.
, Weintraub
H.
, Buckingham
M.
(1989
) Expression of two myogenic regulatory factors myogenin and MyoD1 during mouse embryogenesis.
Nature
341
, 303
–307
Sporle
R.
, Gunther
T.
, Struwe
M.
, Schughart
K.
(1996
) Severe defects in the formation of epaxial musculature in open brain (opb) mutant mouse embryos.
Development
122
, 79
–86
Tajbakhsh
S.
, Bober
E.
, Babinet
C.
, Pournin
S.
, Arnold
H.
, Buckingham
M.
(1996
) Gene targeting the myf-5 locus with nlacZ reveals expression of this myogenic factor in mature skeletal muscle fibres as well as early embryonic muscle.
Dev. Dyn
206
, 291
–300
Tajbakhsh
S.
, Borello
U.
, Vivarelli
E.
, Kelly
R.
, Papkoff
J.
, Duprez
D.
, Buckingham
M.
, Cossu
G.
(1998
) Differential activation of Myf5 and MyoD by different Wnts in explants of mouse paraxial mesoderm and the later activation of myogenesis in the absence of Myf5.
Development
125
, 4155
–4162
Tajbakhsh
S.
, Rocancourt
D.
, Buckingham
M.
(1996
) Muscle progenitor cells failing to respond to positional cues adopt non-myogenic fates in myf5 null mice.
Nature
384
, 266
–270
Tajbakhsh
S.
, Rocancourt
D.
, Cossu
G.
, Buckingham
M.
(1997
) Redefining the genetic hierarchies controlling skeletal myogenesis: Pax-3 and Myf-5 act upstream of MyoD.
Cell
89
, 127
–138
Teillet
M.-A.
, Watanabe
Y.
, Jeffs
P.
, Duprez
D.
, Lapointe
F.
, Le Dourain
N. M.
(1998
) Sonic hedgehog is required for survival of both myogenic and chondrogenic somitic lineages.
Development
125
, 2019
–2030
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
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1999
