beta-Thymosins are polypeptides that bind monomeric actin and thereby function as actin buffers in many cells. We show that during zebrafish development, β-thymosin expression is tightly correlated with neuronal growth and differentiation. It is transiently expressed in a subset of axon-extending neurons, essentially primary neurons that extend long axons, glia and muscle. Non-neuronal expression in the brain is restricted to a subset of glia surrounding newly forming axonal tracts. Skeletal muscle cells in somites, jaw and fin express beta-thymosin during differentiation, coinciding with the time of innervation. Injection of beta-thymosin antisense RNA into zebrafish embryos results in brain defects and impairment of the development of beta-thymosin-associated axon tracts. Furthermore, irregularities in somite formation can be seen in a subset of embryos. Compared to wild-type, antisense-injected embryos show slightly weaker and more diffuse engrailed staining at the midbrain-hindbrain boundary and a strong reduction of Isl-1 labeling in Rohon Beard and trigeminal neurons. The decreased expression is not based on a loss of neurons indicating that beta-thymosin may be involved in the maintenance of the expression of molecules necessary for neuronal differentiation. Taken together, our results strongly indicate that beta-thymosin is an important regulator of development.

Reference

Alexandre
D.
,
Clarke
J. D.
,
Oxtoby
E.
,
Yan
Y. L.
,
Jowett
T.
,
Holder
N.
(
1996
)
Ectopic expression of Hoxa-1 in the zebrafish alters the fate of the mandibular arch neural crest and phenocopies a retinoic acid-induced phenotype.
Development
122
,
735
746
Arber
S.
,
Barbayannis
F. A.
,
Hanser
H.
,
Schneider
C.
,
Stanyon
C. A.
,
Bernard
O.
,
Caroni
P.
(
1998
)
Regulation of actin dynamics through phosphorylation of cofilin by LIM-kinase [see comments].
Nature
393
,
805
809
Barth
K. A.
,
Wilson
S. W.
(
1995
).
Expression of zebrafish nk2.2 is influenced by sonic hedgehog/vertebrate hedgehog-1 and demarcates a zone of neuronal differentiation in the embryonic forebrain.
Development
121
,
1755
1768
Bentley
D.
,
O'Connor
T. P.
(
1994
)
Cytoskeletal events in growth cone steering.
Curr. Opin. Neurobiol
4
,
43
48
Bentley
D.
,
Toroian-Raymond
A.
(
1986
)
Disoriented pathfinding by pioneer neurone growth cones deprived of filopodia by cytochalasin treatment.
Nature
323
,
712
715
Bernhardt
R. R.
,
Tongiorgi
E.
,
Anzini
P.
,
Schachner
M.
,
Bernhardt
R. R.
,
Tongiorgi
E.
,
Anzini
P.
,
Schachner
M.
(
1996
)
Increased expression of specific recognition molecules by retinal ganglion cells and by optic pathway glia accompanies the successful regeneration of retinal axons in adult zebrafish.
J. Comp. Neurol
376
,
253
264
Cantiello
H. F.
,
Patenaude
C.
,
Zaner
K.
(
1991
)
Osmotically induced electrical signals from actin filaments.
Biophys. J
59
,
1284
1289
Chien
C. B.
,
Rosenthal
D. E.
,
Harris
W. A.
,
Holt
C. E.
(
1993
)
Navigational errors made by growth cones without filopodia in the embryonic Xenopus brain.
Neuron
11
,
237
251
Chitnis
A. B.
,
Kuwada
J. Y.
(
1990
)
Axonogenesis in the brain of zebrafish embryos.
J. Neurosci
10
,
1892
1905
Condon
M. R.
,
Hall
A. K.
(
1992
)
Expression of thymosin beta-4 andrelated genes in developing human brain.
J. Mol. Neurosci
3
,
165
170
de la Brousse
F. C.
,
Emerson
C. P.
Jr
(
1990
)
Localized expression of a myogenic regulatory gene, qmf1, in the somite dermatome of avian embryos.
Genes Dev
4
,
567
581
Dlugosz
A. A.
,
Antin
P. B.
,
Nachmias
V. T.
,
Holtzer
H.
(
1984
)
The relationship between stress fiber-like structures and nascent myofibrils in cultured cardiac myocytes.
J. Cell. Biol
99
,
2268
2278
Erickson-Viitanen
S.
,
Ruggieri
S.
,
Natalini
P.
,
Horecker
B. L.
(
1983
)
Thymosin beta 10, a new analog of thymosin beta 4 in mammalian tissues.
Arch. Biochem. Biophys
225
,
407
413
Ericson
J.
,
Thor
S.
,
Edlund
T.
,
Jessell
T. M.
,
Yamada
T.
(
1992
)
Early stages of motor neuron differentiation revealed by expression of homeobox gene Islet-1.
Science
256
,
1555
1560
Felsenfeld
A. L.
,
Curry
M.
,
Kimmel
C. B.
(
1991
)
The fub-1 mutation blocks initial myofibril formation in zebrafish muscle pioneer cells.
Dev. Biol
148
,
23
30
Fernandez-Valle
C.
,
Gorman
D.
,
Gomez
A. M.
,
Bunge
M. B.
(
1997
)
Actin plays a role in both changes in cell shape and gene-expression associated with Schwann cell myelination.
J. Neurosci
17
,
241
250
Golla
R.
,
Philp
N.
,
Safer
D.
,
Chintapalli
J.
,
Hoffman
R.
,
Collins
L.
,
Nachmias
V. T.
(
1997
)
Co-ordinate regulation of the cytoskeleton in 3T3 cells overexpressing thymosin-beta4.
Cell Motil. Cytoskeleton
38
,
187
200
Gottlieb
T. A.
,
Ivanov
I. E.
,
Adesnik
M.
,
Sabatini
D. D.
(
1993
)
Actin microfilaments play a critical role in endocytosis at the apical but not the basolateral surface of polarized epithelial cells.
J. Cell Biol
120
,
695
710
Granato
M.
,
van Eeden
F. J.
,
Schach
U.
,
Trowe
T.
,
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.
,
Nusslein-Volhard
C.
(
1996
)
Genes controlling and mediating locomotion behavior of the zebrafish embryo and larva.
Development
123
,
399
413
Grant
D. S.
,
Kinsella
J. L.
,
Kibbey
M. C.
,
LaFlamme
S.
,
Burbelo
P. D.
,
Goldstein
A. L.
,
Kleinman
H. K.
(
1995
)
Matrigel induces thymosin beta 4 gene in differentiating endothelial cells.
J. Cell. Sci
108
,
3685
3694
Hall
A. K.
(
1995
)
Thymosin beta-10 accelerates apoptosis.
Cell. Mol. Biol. Res
41
,
167
180
Hannappel
E.
,
Xu
G. J.
,
Morgan
J.
,
Hempstead
J.
,
Horecker
B. L.
(
1982
)
Thymosin beta 4: a ubiquitous peptide in rat and mouse tissues.
Proc. Natl. Acad. Sci. USA
79
,
2172
2175
Hansson
A.
,
Skoglund
G.
,
Lassing
I.
,
Lindberg
U.
,
Ingelman-Sundberg
M.
(
1988
)
Protein kinase C-dependent phosphorylation of profilin is specifically stimulated by phosphatidylinositol bisphosphate (PIP2).
Biochem. Biophys. Res. Commun
150
,
526
531
Hatta
K.
,
Bremiller
R.
,
Westerfield
M.
,
Kimmel
C. B.
(
1991
)
Diversity of expression of engrailed-like antigens in zebrafish.
Development
112
,
821
832
Hauptmann
G.
,
Gerster
T.
(
1994
)
Two-color whole-mount in situ hybridization to vertebrate and Drosophila embryos.
Trends Genet
10
,
266
–.
Kamiguchi
H.
,
Long
K. E.
,
Pendergast
M.
,
Schaefer
A. W.
,
Rapoport
I.
,
Kirchhausen
T.
,
Lemmon
V.
(
1998
)
The neural cell adhesion molecule L1 interacts with the AP-2 adaptor and is endocytosed via the clathrin-mediated pathway.
J. Neurosci
18
,
5311
5321
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
Lamaze
C.
,
Fujimoto
L. M.
,
Yin
H. L.
,
Schmid
S. L.
(
1997
)
The actin cytoskeleton is required for receptor-mediated endocytosis in mammalian cells.
J. Biol. Chem
272
,
20332
20335
Leonard
D. G.
,
Ziff
E. B.
,
Greene
L. A.
(
1987
)
Identification and characterization of mRNAs regulated by nerve growth factor in PC12 cells.
Mol. Cell. Biol
7
,
3156
3167
Lugo
D. I.
,
Chen
S. C.
,
Hall
A. K.
,
Ziai
R.
,
Hempstead
J. L.
,
Morgan
J. I.
(
1991
)
Developmental regulation of beta-thymosins in the rat central nervous system.
J. Neurochem
56
,
457
461
Martini
R.
(
1994
)
Expression and functional roles of neural cell surface molecules and extracellular matrix components during development and regeneration of peripheral nerves.
J. Neurocytol
23
,
1
28
Matsudaira
P.
,
Janmey
P.
(
1988
)
Pieces in the actin-severing protein puzzle.
Cell
54
,
139
140
Mays
R. W.
,
Beck
K. A.
,
Nelson
W. J.
(
1994
)
Organization and function of the cytoskeleton in polarized epithelial cells: a component of the protein sorting machinery.
Curr. Opin. Cell Biol
6
,
16
24
Mohun
T. J.
,
Brennan
S.
,
Dathan
N.
,
Fairman
S.
,
Gurdon
J. B.
(
1984
)
Cell type-specific activation of actin genes in the early amphibian embryo.
Nature
311
,
716
721
Muallem
S.
,
Kwiatkowska
K.
,
Xu
X.
,
Yin
H. L.
(
1995
)
Actin filamentdisassembly is a sufficient final trigger for exocytosis in nonexcitable cells.
J. Cell Biol
128
,
589
598
Mundigl
O.
,
Ochoa
G. C.
,
David
C.
,
Slepnev
V. I.
,
Kabanov
A.
,
De Camilli
P.
(
1998
)
Amphiphysin I antisense oligonucleotides inhibit neurite outgrowth in cultured hippocampal neurons.
J. Neurosci
18
,
93
103
Myers
P. Z.
,
Eisen
J. S.
,
Westerfield
M.
(
1986
)
Development and axonal outgrowth of identified motoneurons in the zebrafish.
J. Neurosci
6
,
2278
2289
Nachmias
V. T.
(
1993
)
Small actin-binding proteins: the beta-thymosin family.
Curr. Opin. Cell Biol
5
,
56
62
Patel
N. H.
,
Martin-Blanco
E.
,
Coleman
K. G.
,
Poole
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
Prat
A. G.
,
Cantiello
H. F.
(
1996
)
Nuclear ion channel activity is regulated by actin filaments.
Am. J. Physiol
270
,
1532
1543
Roth
M. B.
,
Zahler
A. M.
,
Stolk
J. A.
(
1991
)
A conserved family of nuclear phosphoproteins localized to sites of polymerase II transcription.
J. Cell. Biol
115
,
587
596
Rupp
R. A.
,
Snider
L.
,
Weintraub
H.
(
1994
)
Xenopus embryos regulate the nuclear localization of XMyoD.
Genes Dev
8
,
1311
1323
Sohn
R. H.
,
Goldschmidt-Clermont
P. J.
(
1994
)
Profilin: at the crossroads of signal transduction and the actin cytoskeleton.
BioEssays
16
,
465
472
Sun
H. Q.
,
Kwiatkowska
K.
,
Yin
H. L.
(
1995
)
Actin monomer binding proteins.
Curr. Opin. Cell Biol
7
,
102
110
Tear
G.
,
Harris
R.
,
Sutaria
S.
,
Kilomanski
K.
,
Goodman
C. S.
,
Seeger
M. A.
(
1996
)
commissureless controls growth cone guidance across the Cns midline in Drosophila and encodes a novel membrane protein.
Neuron
16
,
501
514
Theriot
J. A.
(
1994
)
Regulation of the actin cytoskeleton in living cells.
Semin. Cell Biol
5
,
193
199
Thisse
C.
,
Thisse
B.
,
Schilling
T. F.
,
Postlethwait
J. H.
(
1993
)
Structure of the zebrafish snail1 gene and its expression in wild-type, spadetail and no tail mutant embryos.
Development
119
,
1203
1215
Turner
D. L.
,
Weintraub
H.
(
1994
)
Expression of achaete-scute homolog 3 in Xenopus embryos converts ectodermal cells to a neural fate.
Genes Dev
8
,
1434
1447
Williams
B. A.
,
Ordahl
C. P.
(
1994
)
Pax-3 expression in segmental mesoderm marks early stages in myogenic cell specification.
Development
120
,
785
796
Wu
W.
,
Toma
J. G.
,
Chan
H.
,
Smith
R.
,
Miller
F. D.
(
1994
)
Disruption of fast axonal transport in vivo leads to alterations in Schwann cell gene expression.
Dev. Biol
163
,
423
439
Yamamoto
T.
,
Gotoh
M.
,
Kitajima
M.
,
Hirohashi
S.
(
1993
)
Thymosin beta-4 expression is correlated with metastatic capacity of colorectal carcinomas.
Biochem. Biophys. Res. Commun
193
,
706
710
Yamamoto
M.
,
Yamagishi
T.
,
Yaginuma
H.
,
Murakami
K.
,
Ueno
N.
(
1994
)
Localization of thymosin beta 4 to the neural tissues during the development of Xenopus laevis, as studied by in situ hybridization and immunohistochemistry.
Brain Res. Dev. Brain. Res
79
,
177
185
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