The mechanisms underlying neuronal specification and axonogenesis in the vertebrate hindbrain are poorly understood. To address these questions, we have employed anatomical methods and mutational analysis to characterize the branchiomotor neurons in the zebrafish embryo. The zebrafish branchiomotor system is similar to those in the chick and mouse, except for the location of the nVII and nIX branchiomotor neurons. Developmental analyses of genes expressed by branchiomotor neurons suggest that the different location of the nVII neurons in the zebrafish may result from cell migration. To gain insight into the mechanisms underlying the organization and axonogenesis of these neurons, we examined the development of the branchiomotor pathways in neuronal mutants. The valentino b337 mutation blocks the formation of rhombomeres 5 and 6, and severely affects the development of the nVII and nIX motor nuclei. The cyclops b16 mutation deletes ventral midline cells in the neural tube, and leads to a severe disruption of most branchiomotor nuclei and axon pathways. These results demonstrate that rhombomere-specific cues and ventral midline cells play important roles in the development of the branchiomotor pathways.

REFERENCES

REFERENCES
Akimenko
M. A.
,
Ekker
M.
,
Wegner
J.
,
Lin
W.
,
Westerfield
M.
(
1994
)
Combinatorial expression of three zebrafish genes related to distal-less: part of a homeobox gene code for the head.
J. Neurosci
14
,
3475
3486
Appel
B.
,
Korzh
V.
,
Glasgow
E.
,
Thor
S.
,
Edlund
T.
,
Dawid
I. B.
,
Eisen
J. S.
(
1995
)
Motoneuron fate specification revealed by patterned LIM homeobox gene expression in embryonic zebrafish.
Development
121
,
4117
4125
Bernhardt
R. R.
,
Nguyen
N.
,
Kuwada
J. Y.
(
1992
)
Growth cone guidance by floor plate cells in the spinal cord of zebrafish embryos.
Neuron
8
,
869
882
Bernhardt
R. R.
,
Patel
C. K.
,
Wilson
S. W.
,
Kuwada
J. Y.
(
1992
)
Axonal trajectories and distribution of GABAergic spinal neurons in wildtype and mutant zebrafish lacking floor plate cells.
J. Comp. Neurol
326
,
263
272
Birgbauer
E.
,
Fraser
S. E.
(
1994
)
Violation of cell lineage restriction compartments in the chick hindbrain.
Development
120
,
1347
1356
Book
K. J.
,
Morest
D. K.
(
1990
)
Migration of neuroblasts by perikaryal translocation: Role of cellular elongation and axonal outgrowth in the acoustic nuclei of the chick embryo medulla.
J. Comp. Neurol
297
,
55
76
Burrill
J. D.
,
Easter
S. S.
Jr
(
1994
)
Development of the retinofugal projections in the embryonic and larval zebrafish (Brachydanio rerio).
J. Comp. Neurol
346
,
583
600
Carpenter
E. M.
,
Goddard
J. M.
,
Chisaka
O.
,
Manley
N. R.
,
Capecchi
M. R.
(
1993
).
Loss of Hox-a1 (Hox-1.6) function results in the reorganization of the murine hindbrain.
Development
118
,
1063
1075
Chisaka
O.
,
Musci
T. S.
,
Capecchi
M. R.
(
1992
).
Developmental defects of the ear, cranial nerves and hindbrain resulting from targeted disruption of the mouse homeobox gene Hox-1.6.
Nature
355
,
516
520
Chitnis
A. B.
,
Kuwada
J. Y.
(
1990
)
Axonogenesis in the brain of zebrafish embryos.
J. Neurosci
10
,
1892
1905
Colamarino
S. A.
,
Tessier-Lavigne
M.
(
1995
)
The role of the floor plate in axon guidance.
Annu. Rev. Neurosci
18
,
497
529
Cordes
S. P.
,
Barsh
G. S.
(
1994
)
The mouse segmentation gene kr encodes a novel basic domain-leucine zipper transcription factor.
Cell
79
,
1025
1034
Driever
W.
,
Stemple
D.
,
Schier
A.
,
Solnica-Krezel
L.
(
1994
)
Zebrafish: genetic tools for studying vertebrate development.
Trends Genet
10
,
152
159
Fraser
S.
,
Keynes
R.
,
Lumsden
A.
(
1990
)
Segmentation in the chick embryo hindbrain is defined by cell lineage restrictions.
Nature
344
,
431
435
Fritzsch
B.
,
Christensen
M. A.
,
Nichols
D. H.
(
1993
).
Fiber pathways and positional changes in efferent perikarya of 2.5-to 7-day chick embryos as revealed with DiI and dextran amines.
J. Neurobiol
24
,
1481
1499
Fritzsch
B.
(
1996
)
Development of the labyrinthine efferent system.
Ann. N.Y. Acad. Sci
781
,
21
33
Frohman
M. A.
,
Martin
G. R.
,
Cordes
S. P.
,
Halamek
L. P.
,
Barsh
G. S.
(
1993
)
Altered rhombomere-specific gene expression and hyoid bone differentiation in the mouse segmentation mutant, kreisler (kr).
Development
117
,
925
936
Furley
A. J.
,
Morton
S. B.
,
Manalo
D.
,
Karagogeos
D.
,
Dodd
J.
,
Jessell
T. M.
(
1990
)
The axonal glycoprotein TAG-1 is an immunoglobulin superfamily member with neurite outgrowth-promoting activity.
Cell
61
,
157
170
Gilland
E.
,
Baker
R.
(
1992
)
Longitudinal and tangential migration ofcranial nerve efferent neurons in the developing hindbrain of Squalus acanthias.
Biol. Bull
183
,
356
358
Gilland
E.
,
Baker
R.
(
1993
)
Conservation of neuroepithelial and mesodermal segments in the embryonic vertebrate head.
Acta Anat
148
,
110
123
Goddard
J. M.
,
Rossel
M.
,
Manley
N. R.
,
Capecchi
M. R.
(
1996
)
Mice with targeted disruption of Hoxb-1 fail to form the motor nucleus of the VIIth nerve.
Development
122
,
3217
3228
Goodman
C. S.
,
Shatz
C. J.
(
1993
)
Developmental mechanisms that generate precise patterns of neuronal connectivity.
Neuron
10
,
77
98
Greenspoon
S.
,
Patel
C. K.
,
Hashmi
S.
,
Bernhardt
R. R.
,
Kuwada
J. Y.
(
1995
)
The notochord and floor plate guide growth cones in the zebrafish spinal cord.
J. Neurosci
15
,
5956
5965
Guthrie
S.
,
Pini
A.
(
1995
)
Chemorepulsion of developing motor axons by the floor plate.
Neuron
14
,
1117
1130
Hatta
K.
,
Schilling
T. F.
,
BreMiller
R. A.
,
Kimmel
C. B.
(
1990
)
Specification of jaw muscle identity in zebrafish: correlation with engrailed-homeoprotein expression.
Science
250
,
802
805
Hatta
K.
,
Kimmel
C. B.
,
Ho
R. K.
,
Walker
C.
(
1991
)
The cyclops mutation blocks specification of the floor plate of the zebrafish central nervous system.
Nature
350
,
339
341
Hatta
K.
(
1992
)
Role of the floor plate in axonal patterning in the zebrafish CNS.
Neuron
9
,
629
642
Inoue
A.
,
Takahashi
M.
,
Hatta
K.
,
Hotta
Y.
,
Okamoto
H.
(
1994
)
Developmental regulation of islet-1 mRNA expression during neuronal differentiation in embryonic zebrafish.
Dev. Dyn
199
,
1
11
Kanki
J. P.
,
Chang
S.
,
Kuwada
J. Y.
(
1994
)
The molecular cloning and characterization of potential chick DM-GRASP homologs in zebrafish and mouse.
J. Neurobiol
25
,
831
845
Kimmel
C. B.
,
Metcalfe
W. K.
,
Schabtach
E.
(
1985
)
T reticular interneurons: a class of serially repeating cells in the zebrafish hindbrain.
J. Comp. Neurol
233
,
365
376
Kimmel
C. B.
(
1993
)
Patterning the brain of the zebrafish embryo.
Annu. Rev. Neurosci
16
,
707
732
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
Korzh
V.
,
Edlund
T.
,
Thor
S.
(
1993
)
Zebrafish primary neurons initiate expression of the LIM homeodomain protein Isl-1 at the end of gastrulation.
Development
118
,
417
425
Kuwada
J. Y.
,
Bernhardt
R. R.
,
Chitnis
A. B.
(
1990
)
Pathfinding by identified growth cones in the spinal cord of zebrafish embryos.
J. Neurosci
10
,
1299
1308
Kuwada
J. Y.
(
1995
)
Development of the zebrafish nervous system: genetic analysis and manipulation.
Curr. Opin. Neurobiol
5
,
50
54
Lubke
J.
(
1993
)
Photoconversion of diaminobenzidine with different fluorescent neuronal markers into a light and electron microscopic dense reaction product.
Micro. Res. Tech
24
,
2
14
Lufkin
T.
,
Dierich
A.
,
LeMeur
M.
,
Mark
M.
,
Chambon
P.
(
1991
).
Disruption of the Hox-1.6 homeobox gene results in defects in a region corresponding to its rostral domain of expression.
Cell
66
,
1105
1119
Lumsden
A.
,
Keynes
R.
(
1989
)
Segmental patterns of neuronal development in the chick hindbrain.
Nature
337
,
424
428
Lumsden
A.
,
Krumlauf
R.
(
1996
)
Patterning the vertebrate neuraxis.
Science
274
,
1109
1115
Lumsden
A.
,
Sprawson
N.
,
Graham
A.
(
1991
)
Segmental origin and migration of neural crest cells in the hindbrain region of the chick embryo.
Development
113
,
1281
1291
Marin
F.
,
Puelles
L.
(
1995
)
Morphological fate of rhombomeres in quail/chick chimeras: A segmental analysis of hindbrain nuclei.
Eur. Jour. Neurosci
7
,
1714
1738
Marshall
H.
,
Nonchev
S.
,
Sham
M. H.
,
Muchamore
I.
,
Lumsden
A.
,
Krumlauf
R.
(
1992
)
Retinoic acid alters hindbrain Hox code and induces transformation of rhombomeres 2/3 into a 4/5 identity.
Nature
360
,
737
741
McConnell
S. K.
(
1995
)
Strategies for the generation of neuronal diversity in the developing central nervous system.
J. Neurosci
15
,
6987
6998
McKay
I. J.
,
Muchamore
I.
,
Krumlauf
R.
,
Maden
M.
,
Lumsden
A.
,
Lewis
J.
(
1994
)
The kreisler mouse: a hindbrain segmentation mutant that lacks two rhombomeres.
Development
120
,
2199
2211
Moens
C. B.
,
Yan
Y.-L.
,
Appel
B.
,
Force
A.
,
Kimmel
C. B.
(
1996
)
valentino: a zebrafish gene required for normal hindbrain segmentation.
Development
122
,
3981
3990
Moody
S. A.
,
Heaton
M. B.
(
1983
)
Developmental relationships between trigeminal ganglia and trigeminal motoneurons in chick embryos. II. Ganglion axon ingrowth guides motoneuron migration.
J. Comp. Neurol
213
,
344
349
Noden
D. M.
(
1983
)
The role of the neural crest in patterning of avian cranial skeletal, connective and muscle tissues.
Dev. Biol
96
,
144
165
Nusslein-Volhard
C.
(
1994
)
Of flies and fishes.
Science
266
,
572
574
Panganiban
G.
,
Sebring
A.
,
Nagy
L.
,
Carroll
S.
(
1995
)
The development of crustacean limbs and the evolution of arthropods.
Science
270
,
1363
1367
Pfaff
S. L.
,
Mendelsohn
M.
,
Stewart
C. L.
,
Edlund
T.
,
Jessell
T. M.
(
1996
)
Requirement for LIM homeobox gene Isl1 in motor neuron generation reveals a motor neuron-dependent step in interneuron differentiation.
Cell
84
,
309
320
Piperno
G.
,
Fuller
M. T.
(
1985
)
Monoclonal antibodies specific for an acetylated form of alpha-tubulin recognize the antigen in cilia and flagella from a variety of organisms.
J. Cell Biol
101
,
2085
2094
Schilling
T. F.
,
Kimmel
C. B.
(
1994
)
Segment and cell type lineage restrictions during pharyngeal arch development in the zebrafish embryo.
Development
120
,
483
494
Schneider-Maunoury
S.
,
Topilko
P.
,
Seitandou
T.
,
Levi
G.
,
Cohen-Tannoudji
M.
,
Pournin
S.
,
Babinet
C.
,
Charnay
P.
(
1993
)
Disruption of Krox-20 results in alteration of rhombomeres 3 and 5 in the developing hindbrain.
Cell
75
,
1199
1214
Stoeckli
E. T.
,
Landmesser
L. T.
(
1995
)
Axonin-1, Nr-CAM, and Ng-CAM play different roles in the in vivo guidance of chick commissural neurons.
Neuron
14
,
1165
1179
Studer
M.
,
Lumsden
A.
,
Ariza-McNaughton
L.
,
Bradley
A.
,
Krumlauf
R.
(
1996
)
Altered segmental identity and abnormal migration of motor neurons in mice lacking Hoxb-1.
Nature
384
,
630
634
Swiatek
P. J.
,
Gridley
T.
(
1993
)
Perinatal lethality and defects in hindbrain development in mice homozygous for a targeted mutation of the zinc finger gene Krox20.
Genes Dev
7
,
2071
2084
Tanabe
Y.
,
Jessell
T. M.
(
1996
)
Diversity and pattern in the developing spinal cord.
Science
274
,
1115
1123
Trevarrow
B.
,
Marks
D. L.
,
Kimmel
C. B.
(
1990
)
Organization of hindbrain segments in the zebrafish embryo.
Neuron
4
,
669
679
Wake
D. B.
(
1993
)
Brainstem organization and branchiomeric nerves.
Acta Anat
148
,
124
131
This content is only available via PDF.