The Rho subfamily of Ras-related small GTPases participates in a variety of cellular events including organization of the actin cytoskeleton and signalling by c-Jun N-terminal kinase and p38 kinase cascades. These functions of the Rho subfamily are likely to be required in many developmental events. We have been studying the participation of the RHO subfamily in dorsal closure of the Drosophila embryo, a process involving morphogenesis of the epidermis. We have previously shown that Drac1, a Rho subfamily protein, is required for the presence of an actomyosin contractile apparatus believed to be driving the cell shape changes essential to dorsal closure. Expression of a dominant negative Drac1 transgene causes a loss of this contractile apparatus from the leading edge of the advancing epidermis and dorsal closure fails. We now show that two other Rho subfamily proteins, Dcdc42 and RhoA, as well as Ras1 are also required for dorsal closure. Dcdc42 appears to have conflicting roles during dorsal closure: establishment and/or maintenance of the leading edge cytoskeleton versus its down regulation. Down regulation of the leading edge cytoskeleton may be controlled by the serine/threonine kinase DPAK, a potential Drac1/Dcdc42 effector. RhoA is required for the integrity of the leading edge cytoskeleton specifically in cells flanking the segment borders. We have begun to characterize the interactions of the various small GTPases in regulating dorsal closure and find no evidence for the hierarchy of Rho subfamily activity described in some mammalian cell types. Rather, our results suggest that while all Ρ subfamily p21s tested are required for dorsal closure, they act largely in parallel.

REFERENCES

Allen
W. E.
,
Jones
G. E.
,
Pollard
J. W.
,
Ridley
A. J.
(
1997
).
Rho, Rac and Cdc42 regulate actin organization and cell adhesion in macrophages.
J. Cell Sci
110
,
707
720
Barrett
K.
,
Leptin
M.
,
Settleman
J.
(
1997
).
The Rho GTPase and a putative RhoGEF mediate a signaling pathway for the cell shape changes in Drosophila gastrulation.
Cell
91
,
905
915
Brand
A. H.
,
Perrimon
N.
(
1993
).
Targeted gene expression as a means of altering cell fates and generating dominant phenotypes.
Development
118
,
401
415
Brown
N. H.
(
1993
).
Integrins hold Drosophila together.
BioEssays
15
,
383
390
Crawford
J. M.
,
Harden
N.
,
Leung
T.
,
Lim
L.
,
Kiehart
D. P.
(
1998
).
Cellularization in Drosophila melanogaster is disrupted by the inhibition of Rho activity and the activation of Cdc42 function.
Dev. Biol
204
,
151
164
Dharmawardhane
S.
,
Sanders
L. C.
,
Martin
S. S.
,
Daniels
R. H.
,
Bokoch
G. M.
(
1997
).
Localization of p21-activated kinase 1 (PAK1) to pinocytic vesicles and cortical actin structures in stimulated cells.
J. Cell Biol
138
,
1265
1278
Dickson
B.
,
Hafen
E.
(
1994
).
Genetics of signal transduction in invertebrates.
Curr. Opin. Genet. Dev
4
,
64
70
Eaton
S.
,
Auvinen
P.
,
Luo
L.
,
Jan
Y. N.
,
Simons
K.
(
1995
).
CDC42 and Rac1 control different actin-dependent processes in the Drosophila wing disc epithelium.
J. Cell Biol
131
,
151
164
Eaton
S.
,
Wepf
R.
,
Simons
K.
(
1996
).
Roles for Rac1 and Cdc42 in planar polarization and hair outgrowth in the wing of Drosophila.
J. Cell Biol
135
,
1277
1289
Glise
B.
,
Bourbon
H.
,
Noselli
S.
(
1995
).
hemipterous encodes a novel Drosophila MAP kinase kinase, required for epithelial cell sheet movement.
Cell
83
,
451
461
Glise
B.
,
Noselli
S.
(
1997
).
Coupling of Jun amino-terminal kinase and Decapentaplegic signaling pathways in Drosophila morphogenesis.
Genes Dev
11
,
1738
1747
Harden
N.
,
Loh
H. Y.
,
Chia
W.
,
Lim
L.
(
1995
).
A dominant inhibitory version of the small GTP-binding protein Rac disrupts cytoskeletalstructures and inhibits developmental cell shape changes in Drosophila.
Development
121
,
903
914
Harden
N.
,
Lee
J.
,
Loh
H.-Y.
,
Ong
Y.-M.
,
Tan
I.
,
Leung
T.
,
Manser
E.
,
Lim
L.
(
1996
).
A Drosophila homolog of the Rac-and Cdc42-activated serine/threonine kinase PAK is a potential focal adhesion and focal complex protein that colocalizes with dynamic actin structures.
Mol. Cell. Biol
16
,
1896
1908
Hariharan
I. K.
,
Hu
K.-Q.
,
Asha
H.
,
Quintanilla
A.
,
Ezzell
R. M.
,
Settleman
J.
(
1995
).
Characterization of rho GTPase family homologues in Drosophilamelanogaster: overexpressing Rho1 in retinal cells causes a late developmental defect.
EMBO J
14
,
292
302
Hinz
U.
,
Giebel
B.
,
Campos-Ortega
J. A.
(
1994
).
The basic-helix-loop-helix domain of Drosophila lethal of scute protein is sufficient for proneural function and activates neurogenic genes.
Cell
76
,
77
87
Hou
X. S.
,
Goldstein
E. S.
,
Perrimon
N.
(
1997
).
Drosophila Jun relays the Jun amino-terminal kinase signal transduction pathway to the Decapentaplegic signal transduction pathway in regulating epithelial cell sheet movement.
Genes Dev
11
,
1728
1737
Kaufmann
N.
,
Wills
Z. P.
,
Van Vactor
D.
(
1998
).
Drosophila Rac1 controls motor axon guidance.
Development
125
,
453
461
Kiehart
D. P.
,
Feghali
R.
(
1986
).
Cytoplasmic myosin from Drosophila melanogaster.
J. Cell Biol
103
,
1517
1525
Knust
E.
(
1997
).
Drosophila morphogenesis: movements behind the edge.
Curr.Biol
7
,
558
–.
Kockel
L.
,
Zeitlinger
J.
,
Staszewski
L. M.
,
Mlodzik
M.
,
Bohmann
D.
(
1997
).
Jun in Drosophila development: redundant and nonredundant functions and regulation by two MAPK signal transduction pathways.
Genes Dev
11
,
1748
1758
Kozma
R.
,
Ahmed
S.
,
Best
A.
,
Lim
L.
(
1995
).
The Ras-related protein Cdc42Hs and bradykinin promote formation of peripheral actin microspikes and filopodia in Swiss 3T3 fibroblasts.
Mol. Cell. Biol
15
,
1942
1952
Kozma
R.
,
Sarner
S.
,
Ahmed
S.
,
Lim
L.
(
1997
).
Rho family GTPases and neuronal growth cone remodelling: relationship between increased complexity induced by Cdc42Hs, Rac1, and acetylcholine and collapse induced by RhoA and lysophosphatidic acid.
Mol. Cell. Biol
17
,
1201
1211
Lee
T.
,
Feig
L.
,
Montell
D. J.
(
1996
).
Two distinct roles for Ras in a developmentally regulated cell migration.
Development
122
,
409
418
Leung
T.
,
Manser
E.
,
Tan
L.
,
Lim
L.
(
1995
).
A novel serine/threonine kinase binding the Ras-related RhoA GTPase which translocates the kinase to peripheral membranes.
J. Biol. Chem
270
,
29051
29054
Leung
T.
,
Chen
X.-Q.
,
Manser
E.
,
Lim
L.
(
1996
).
The p160 RhoA-binding kinase ROKis a member of a kinase family and is involved in the reorganization of the cytoskeleton.
Mol. Cell. Biol
16
,
5313
5327
Lim
L.
,
Manser
E.
,
Leung
T.
,
Hall
C.
(
1996
).
Regulation of phosphorylation pathways by p21 GTPases. The p21 Ras-related Rho subfamily and its role in phosphorylation signalling pathways.
Eur. J. Biochem
242
,
171
185
Lu
X.
,
Chou
T.-B.
,
Williams
N. G.
,
Roberts
T.
,
Perrimon
N.
(
1993
).
Control of cell fate determination by p21ras/Ras1, an essential component of torso signaling in Drosophila.
Genes Dev
7
,
621
632
Luo
L.
,
Liao
Y. J.
,
Jan
L. Y.
,
Jan
Y. N.
(
1994
).
Distinct morphogenetic functions of similar small GTPases: Drosophila Drac1 is involved in axonal outgrowth and myoblast fusion.
Genes Dev
8
,
1787
1802
Luo
L.
,
Hensch
T. K.
,
Ackerman
L.
,
Barbel
S.
,
Jan
L. Y.
,
Jan
Y. N.
(
1996
).
Differential effects of the Rac GTPase on Purkinje cell axons and dendritic trunks and spines.
Nature
379
,
837
840
Manser
E.
,
Huang
H.-Y.
,
Loo
T.-H.
,
Chen
X.-Q.
,
Dong
J.-M.
,
Leung
T.
,
Lim
L.
(
1997
).
Expression of constitutively active-PAK reveals effects of the kinase on actin and focal complexes.
Mol. Cell. Biol
17
,
1129
1143
Martin-Blanco
E.
(
1997
).
Regulation of cell differentiation by the Drosophila Jun kinase cascade.
Curr. Opin. Genet. Dev
7
,
666
671
Murphy
A. M.
,
Montell
D. J.
(
1996
).
Cell type-specific roles for Cdc42, Rac, and RhoL in Drosophila oogenesis.
J. Cell Biol
133
,
617
630
Nakano
Y.
,
Guerrero
I.
,
Hidalgo
A.
,
Taylor
A.
,
Whittle
J. R. S.
,
Ingham
P. W.
(
1989
).
A protein with several possible membrane-spanning domains encoded by the Drosophila segment polarity gene patched.
Nature
341
,
508
513
Narumiya
S.
,
Ishizaki
T.
,
Watanabe
N.
(
1997
).
Rho effectors and reorganization of actin cytoskeleton.
FEBS Lett
410
,
68
72
Nobes
C. D.
,
Hall
A.
(
1995
).
Rho, Rac, and Cdc42 GTPases regulate the assembly of multimolecular focal complexes associated with actin stress fibers, lamellipodia, and filopodia.
Cell
81
,
53
62
Noselli
S.
(
1998
).
JNK signaling and morphogenesis in Drosophila.
Trends Genet
14
,
33
38
Qiu
R.-G.
,
Abo
A.
,
McCormick
F.
,
Symons
M.
(
1997
).
Cdc42 regulates anchorage-independent growth and is necessary for Ras transformation.
Mol. Cell. Biol
17
,
3449
3458
Riesgo-Escovar
J. R.
,
Jenni
M.
,
Fritz
A.
,
Hafen
E.
(
1996
).
The Drosophila Jun-N-terminal kinase is required for cell morphogenesis but not for DJun-dependent cell fate specification in the eye.
Genes Dev
10
,
2759
2768
Riesgo-Escovar
J. R.
,
Hafen
E.
(
1997
).
Drosophila Jun kinase regulates expression of decapentaplegic via the ETS-domain protein Aop and the AP-1 transcription factor DJun during dorsal closure.
Genes Dev
11
,
1717
1727
Sluss
H. K.
,
Han
Z.
,
Barrett
T.
,
Davis
R. J.
,
Ip
Y. T.
(
1996
).
A JNKsignal transduction pathway that mediates morphogenesis and an immune response in Drosophila.
Genes Dev
10
,
2745
2758
Strutt
D. I.
,
Weber
U.
,
Mlodzik
M.
(
1997
).
The role of RhoA in tissue polarity and Frizzled signalling.
Nature
387
,
292
295
Symons
M.
(
1996
).
Rho family GTPases: the cytoskeleton and beyond.
Trends Biochem. Sci
21
,
178
181
Tang
Y.
,
Chen
Z.
,
Ambrose
D.
,
Liu
J.
,
Gibbs
J. R.
,
Chernoff
J.
,
Field
J.
(
1997
).
Kinase-deficient Pak1 mutants inhibit Ras transformation of Rat-1 fibroblasts.
Mol. Cell. Biol
17
,
4454
4464
Tang
Y.
,
Marwaha
S.
,
Rutkowski
J. L.
,
Tennekoon
G. I.
,
Phillips
P. C.
,
Field
J.
(
1998
).
A role for Pak protein kinases in Schwann cell transformation.
Proc. Nat. Acad. Sci. USA
95
,
5139
5144
Van Aelst
L.
,
D'Souza-Schorey
C.
(
1997
).
Rho GTPases and signaling networks.
Genes Dev
11
,
2295
2322
Wodarz
A.
,
Hinz
U.
,
Engelbert
M.
,
Knust
E.
(
1995
).
Expression of Crumbs confers apical character on plasma membrane domains of ectodermal epithelia of Drosophila.
Cell
82
,
67
76
Young
P. E.
,
Richman
A. M.
,
Ketchum
A. S.
,
Kiehart
D. P.
(
1993
).
Morphogenesis in Drosophila requires nonmuscle myosin heavy chain function.
Genes Dev
7
,
29
41
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