The developing vertebrate mesencephalon shows a rostrocaudal gradient in the expression of a number of molecular markers and in the cytoarchitectonic differentiation of the tectum, where cells cease proliferating and differentiate in a rostral to caudal progression. Tissue grafting experiments have implicated cell signalling by the mesencephalic-metencephalic (mid-hindbrain) junction (or isthmus) in orchestrating these events. We have explored the role of Wnt-1 and FGF8 signalling in the regulation of mesencephalic polarity. Wnt-1 is expressed in the caudal mesencephalon and Fgf8 in the most rostral metencephalon. Wnt-1 regulates Fgf8 expression in the adjacent metencephalon, most likely via a secondary mesencephalic signal. Ectopic expression of Fgf8 in the mesencephalon is sufficient to activate expression of Engrailed-2 (En-2) and ELF-1, two genes normally expressed in a decreasing caudal to rostral gradient in the posterior mesencephalon. Ectopic expression of Engrailed-1 (En-1), a functionally equivalent homologue of En-2 is sufficient to activate ELF-1 expression by itself. These results indicate the existence of a molecular hierarchy in which FGF8 signalling establishes the graded expression of En-2 within the tectum. This in turn may act to specify other aspects of A-P polarity such as graded ELF-1 expression. Our studies also reveal that FGF8 is a potent mitogen within the mesencephalon: when ectopically expressed, neural precursors continue to proliferate and neurogenesis is prevented. Taken together our results suggest that FGF8 signalling from the isthmus has a key role in coordinately regulating growth and polarity in the developing mesencephalon.
REFERENCES
Adams
B.
, Dorfler
P.
, Aguzzi
A.
, Kozmik
Z.
, Urbanek
P.
, Maurer-Fogy
I.
, Busslinger
M.
(1992
) Pax-5 encodes the transcription factor BSAP and is expressed in B lymphocytes, the developing CNS, and adult testis.
Genes Dev
6
, 1589
–1607
Altman
J.
, Bayer
S. A.
(1981
) Time of origin of neurons of the rat inferior colliculus and the relations between cytogenesis and tonotopic order in the auditory pathway.
Exp. Brain Res
42
, 411
–423
Altman
J.
, Bayer
S. A.
(1981
) Time of origin of neurons of the rat superior colliculus in relation to other components of the visual and visuomotor pathways.
Exp. Brain Res
42
, 424
–434
Alvarado-Mallart
R.-M.
, Martinez
S.
, Lance-Jones
C. C.
(1990
) Pluripotentiality of the 2-day-old avian germinative neuroepithelium.
Dev. Biol
139
, 75
–88
Asano
M.
, Gruss
P.
(1992
) Pax-5 is expressed at the midbrain-hindbrain boundary during mouse development.
Mech. Dev
39
, 29
–39
Bally-Cuif
L.
, Alvarado-Mallart
R.-M.
, Darnell
D. K.
, Wassef
M.
(1992
) Relationship between Wnt-1 and En-2 expression domains during early development of normal and ectopic met-mesencephalon.
Development
115
, 999
–1009
Bally-Cuif
L.
, Wassef
M.
(1994
) Ectopic induction and reorganization of Wnt-1 expression in quail/chick chimeras.
Development
120
, 3379
–3394
Bally-Cuif
L.
, Wassef
M.
(1995
) Determination events in the nervous system of the vertebrate embryo.
Curr. Opin. Genet. Dev
5
, 450
–458
Cheng
H.
, Flanagan
J. G.
(1994
) Identification and cloning of ELF-1, a developmentally expressed ligand for the Mek4 and Sek receptor tyrosine kinases.
Cell
79
, 157
–168
Cheng
H.
, Nakamoto
M.
, Bergemann
A. D.
, Flanagan
J. G.
(1995
) Complementary gradients in expression and binding of ELF-1 and Mek-4 in development of the topographic retinotectal projection map.
Cell
82
, 371
–381
Cohn
M. J.
, Izpisua-Belmonte
J.-C.
, Abud
H.
, Heath
J. K.
, Tickle
C.
(1995
) Fibroblast growth factors induce additional limb development from the flank of chick embryos.
Cell
80
, 739
–746
Crossland
W. J.
, Cowan
W. M.
, Rogers
L. A.
, Kelly
J. P.
(1974
) Specification of the retino-tectal projection in the chick.
J. Comp. Neurol
155
, 127
–164
Crossley
P. H.
, Martin
G. R.
(1995
) The mouse Fgf8 gene encodes a family of polypeptides and is expressed in regions that direct outgrowth and patterning in the developing embryo.
Development
121
, 439
–451
Crossley
P. H.
, Martinez
S.
, Martin
G. R.
(1996
) Midbrain development induced by FGF8 in the chick embryo.
Nature
380
, 66
–68
Crossley
P. H.
, Minowada
G.
, MacArthur
C. A.
, Martin
G. R.
(1996
) Roles for FGF8 in the induction, initiation, and maintenance of chick limb development.
Cell
84
, 127
–136
Danielian
P. S.
, McMahon
A. P.
(1996
) Engrailed-1 as a target of the Wnt-1 signalling pathway in vertebrate midbrain development.
Nature
383
, 332
–334
Davis
C. A.
, Joyner
A. L.
(1988
) Expression patterns of the homeobox-containing genes En-1 and En-2 and the proto-oncogene int-1 diverge during mouse development.
Genes Dev
2
, 1736
–1744
Davis
C. A.
, Noble-Topham
S. E.
, Rossant
J.
, Joyner
A. L.
(1988
) Expression patterns of the homeobox containing gene En-2 delineates a specific region in the developing mouse brain.
Genes Dev
2
, 361
–371
DeLong
G. R.
, Coulombre
A. J.
(1965
) Development of the retinotectal projection in the chick embyro.
Exp. Neurol
13
, 351
–363
Dickinson
M. E.
, Krumlauf
R.
, McMahon
A. P.
(1994
) Evidence for a mitogenic effect of Wnt-1 in the developing mammalian central nervous system.
Development
120
, 1453
–1471
Drescher
U.
, Kremoser
C.
, Handwerker
C.
, Loschinger
J.
, Noda
M.
, Bonhoeferr
F.
(1995
) In vitro guidance of retinal ganglion cell axons by RAGS, a 25 kDa tectal protein related to ligands for eph receptor tyrosine kinases.
Cell
82
, 359
–370
Echelard
Y.
, Epstein
D. J.
, St-Jacques
B.
, Shen
L.
, Mohler
J.
, McMahon
J. A.
, McMahon
A. P.
(1993
) Sonic hedgehog, a member of a family of putative signalling molecules, is implicated in the regulation of CNS polarity.
Cell
75
, 1417
–1430
Echelard
Y.
, Vassileva
G.
, McMahon
A. P.
(1994
) Cis -acting regulatory sequences governing Wnt-1 expression in the developing mouse CNS.
Development
120
, 2213
–2224
Friedman
G. C.
, O'Leary
D. D. M.
(1996
) Retroviral misexpression of engrailed genes in the chick optic tectum perturbs the topographic targeting of retinal axons.
J. Neurosci
16
, 5498
–5509
Gardner
C. A.
, Barald
K.
(1992
) Expression patterns of Engrailed-like proteins in the chick embryo.
Dev. Dyn
193
, 370
–388
Gardner
C. A.
, Barald
K. F.
(1991
) The cellular environment controls the expression of engrailed-like protein in the cranial neuroepithelium of quail-chick chimeric embryos.
Development
113
, 1037
–1048
Gardner
C. A.
, Darnell
D. K.
, Poole
S. J.
, Ordahl
C. P.
, Barald
K. F.
(1988
) Expression of an engrailed-like gene during development of the early embryonic chick nervous system.
J. Neurosci. Res
21
, 426
–437
Gensburger
C.
, Labourdette
G.
, Sensenbrenner
M.
(1987
) Brain basic fibroblast growth factor stimulates the proliferation of rat neuronal precursor cells in vitro.
FEBS Lett
217
, 1
–5
Hanks
M.
, Wurst
W.
, Anson-Cartwright
L.
, Auerbach
A. B.
, Joyner
A. L.
(1995
) Rescue of the En-1 mutant phenotype by replacement of En-1 with En-2.
Science
269
, 679
–682
Heikinheimo
M.
, Lawshe
A.
, Shackleford
G. M.
, Wilson
D. B.
, MacArthur
C. A.
(1994
) Fgf-8 expression in the post-gastrulation mouse suggests roles in the development of the face, limbs, and central nervous system.
Mech. Dev
48
, 129
–138
Itasaki
N.
, Ichijo
H.
, Hama
C.
, Matsuno
T.
, Nakamura
H.
(1991
) Establishment of rostrocaudal polarity in tectal primordium: engrailed expression and subsequent tectal polarity.
Development
113
, 1133
–1144
Itasaki
N.
, Nakamura
H.
(1992
) Rostrocaudal polarity of the tectum in birds: correlation of en gradient and topographic order in retinotectal projection.
Neuron
8
, 787
–798
Itasaki
N.
, Nakamura
H.
(1996
) A role for gradient en expression in positional specification on the optic tectum.
Neuron
16
, 55
–62
Joyner
A. L.
(1996
) Engrailed, Wnt and Pax genes regulate midbrain-hindbrain development.
Trends Genet
12
, 15
–20
Kelly
O. G.
, Melton
D. A.
(1995
) Induction and patterning of the vertebrate nervous system.
Trends Genet
11
, 273
–278
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
LaVail
J. H.
, Cowan
W. M.
(1971
) The development of the chick optic tectum. I. Normal morphology and cytoarchitectonic development.
Brain Res
28
, 391
–419
Logan
C.
, Wizenmann
A.
, Drescher
U.
, Monschau
B.
, Bonhoeffer
F.
, Lumsden
A.
(1996
) Rostral optic tectum acquires caudal characteristics following ectopic Engrailed expression.
Curr. Biol
6
, 1006
–1014
MacArthur
C. A.
, Lawshe
A.
, Shanker
D. B.
, Heikenheimo
M.
, Shackleford
G. M.
(1995
) FGF-8 isoforms differ in NIH3T3 cell transforming potential.
Cell Growth Diff
6
, 817
–825
MacArthur
C. A.
, Lawshe
A.
, Xu
J.
, Santos-Ocampo
S.
, Heikinheimo
M.
, Chellaiah
A. T.
, Ornitz
D. M.
(1995
) FGF-8 isoforms activate receptor forms that are expressed in mesenchyme regions of mouse development.
Development
121
, 3603
–3613
Mahmood
R.
, Bresnick
J.
, Hornbruch
A.
, Mahony
C.
, Morton
N.
, Colquhoun
K.
, Martin
P.
, Lumsden
A.
, Dickson
C.
, Mason
I.
(1995
) A role for FGF-8 in the initiation and maintenance of vertebrate limb bud outgrowth.
Curr. Biol
5
, 797
–806
Marin
F.
, Puelles
L.
(1994
) Patterning of the embryonic avian midbrain after experimental inversion: a polarizing activity form the isthmus.
Dev. Biol
163
, 19
–37
Martinez
S.
, Alvarado-Mallart
R.-M.
(1990
) Expression of the homeobox chick-en gene in chick/quail chimeras with inverted mes-metencephalic grafts.
Dev. Biol
139
, 432
–436
Martinez
S.
, Marin
F.
, Nieto
M. A.
, Puelles
L.
(1995
) Induction of ectopic engrailed expression and fate change in avian rhombomeres: intersegmental boundaries as barriers.
Mech. Dev
51
, 289
–303
Martinez
S.
, Wassef
M.
, Alvarado-Mallart
R.-M.
(1991
) Induction of a mesencephalic phenotype in the 2-day-old chick prosencephalon in preceded by the early expression of the homeobox gene en.
Neuron
6
, 971
–981
Matsuno
T.
, Ichijo
H.
, Nakamura
H.
(1991
) Regulation of the rostrocaudal axis of the optic tectum: histological study after rostrocaudal rotation in quail-chick chimeras.
Dev. Brain Res
58
, 265
–270
McMahon
A. P.
, Bradley
A.
(1990
) The Wnt-1 (int-1) proto-oncogene is required for development of a large region of the mouse brain.
Cell
62
, 1073
–1085
McMahon
A. P.
, Joyner
A. L.
, Bradley
A.
, McMahon
J. A.
(1992
). The midbrain-hindbrain phenotype of Wnt-1/Wnt-1 mice results from stepwise deletion of engrailed -expressing cells by 9.5 days postcoitum.
Cell
69
, 581
–595
Millen
K. J.
, Wurst
W.
, Herrup
K.
, Joyner
A. L.
(1994
) Abnormal embryonic cerebellar development and patterning of postnatal foliation in two mouse Engrailed-2 mutants.
Development
120
, 695
–706
Millen
K. J.
, Hui
C.-C.
, Joyner
A.L.
(1995
) A role for En-2 and other murine homologues of Drosophila segment polarity genes in regulating positional information in the developing cerebellum.
Development
121
, 3935
–3945
Millet
S.
, Alvarado-Mallart
R.-M.
(1995
) Expression of the homeobox-containing gene En-2 during the development of the chick central nervous system.
Eur. J. Neurosci
7
, 777
–791
Nakamoto
M.
, Cheng
H.-J.
, Friedman
G. C.
, McLaughlin
T.
, Hansen
M. J.
, Yoon
C. H.
, O'Leary
D. D. M.
, Flanagan
J. G.
(1996
) Topographically specific effects of ELF-1 on retinal axon guidance in vitro and retinal axon mapping in vivo.
Cell
86
, 755
–766
Nornes
H. O.
, Dressler
G. R.
, Knapik
E. W.
, Deutsch
U.
, Gruss
P.
(1990
) Spatially and temporally restricted expression of Pax-2 during murine neurogenesis.
Development
109
, 797
–809
Parr
B. P.
, Shea
M. J.
, Vassileva
G.
, McMahon
A. P.
(1993
) Mouse Wnt genes exhibit discrete domains of expression in the early embryonic CNS and limb buds.
Development
119
, 247
–261
Patel
N. H.
, Martin-Blanceo
E.
, Coleman
K. G. P. S. J.
, Ellis
M.C.
, Kornberg
T. B.
, Goodman
C. S.
(1989
) Expression of engrailed proteins in arthropods, annelids, and chordates.
Cell
58
, 955
–968
Puschel
A. W.
, Westerfield
M.
, Dressler
G. R.
(1992
) Comparative analysis of Pax-2 protein distributions during neurulation in mice and zebrafish.
Mech. Dev
38
, 197
–208
Rowitch
D. H.
, McMahon
A. P.
(1995
) Pax-2 expression in the murine neural plate precedes and encompasses the expression domains of Wnt-1 and En-1.
Mech. Dev
52
, 3
–8
Rubenstein
J. L. R.
, Martinez
S.
, Shimamura
K.
, Puelles
L.
(1994
) The embryonic vertebrate forebrain: the prosomeric model.
Science
266
, 578
–580
Song
D.
, Chalepakis
G.
, Gruss
P.
, Joyner
A. L.
(1996
) Two Pax-binding sites are required for early embryonic brain expression of an Engrailed-2 transgene.
Development
122
, 627
–635
Temple
S.
, Qian
X.
(1995
) bFGF, neurotrophins, and the control of cortical neurogenesis.
Neuron
15
, 249
–252
Thomas
K. R.
, Capecchi
M. R.
(1990
) Targeted disruption of the murine int-1 proto-oncogene resulting in severe abnormalities in midbrain and cerebellar development.
Nature
346
, 847
–850
Urbanek
P.
, Wang
Z.
, Fetla
I.
, Wagner
E. F.
, Busslinger
M.
(1994
) Complete block of early B cell differentialtion and altered patterning of the posterior midbrain in mice lacking Pax5/BSAP.
Cell
79
, 901
–912
Vogel
A.
, Rodriguez
C.
, Izpisua-Belmonte
J.-C.
(1996
) Involvement of FGF-8 in initiation, outgrowth and patterning of the vertebrate limb.
Development
122
, 1737
–1750
Walther
C.
, Gruss
P.
(1991
) Pax-6, a murine paired box gene, is expressed in the developing CNS.
Development
113
, 1435
–1449
Wilkinson
D. G.
, Bailes
J. A.
, McMahon
A. P.
(1987
) Expression of the proto-oncogene int-1 is restricted to specific neural cells in the developing mouse embryo.
Cell
50
, 79
–88
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