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J. Cell Biol., Volume 146, Number 2, July 26, 1999 361-372
Copyright © 1999 by The Rockefeller University Press.

The Drosophila Ral GTPase Regulates Developmental Cell Shape Changes through the Jun NH2-terminal Kinase Pathway

Kazunobu Sawamotoa, Per Wingeb, Shinya Koyamac, Yuki Hirotaa, Chiharu Yamadaa, Sachiyo Miyaoa, Shingo Yoshikawad, Ming-hao Jina,e, Akira Kikuchic, and Hideyuki Okanoa,e
a Division of Neuroanatomy, Department of Neuroscience, Biomedical Research Center, Osaka University Graduate School of Medicine, Osaka 565-0871, Japan
b Unigen Center for Molecular Biology, Norwegian University of Science and Technology, Trondheim N-7005, Norway
c Department of Biochemistry, University of Hiroshima School of Medicine, Hiroshima 734-8551, Japan
d Department of Molecular Neurobiology, Institute of Basic Medical Sciences, University of Tsukuba, Ibaraki 305-0006, Japan
e CREST, Japan Science and Technology Corporation at Division of Neuroanatomy, Department of Neuroscience, Biomedical Research Center, Osaka University Graduate School of Medicine, Osaka 565-0871, Japan

Correspondence to: Hideyuki Okano, Division of Neuroanatomy (D12), Department of Neuroscience, Biomedical Research Center, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan., okano{at}nana.med.osaka-u.ac.jp (E-mail), 81-6-6879-3581 (phone), 81-6-6879-3589 (fax)

The Ral GTPase is activated by RalGDS, which is one of the effector proteins for Ras. Previous studies have suggested that Ral might function to regulate the cytoskeleton; however, its in vivo function is unknown. We have identified a Drosophila homologue of Ral that is widely expressed during embryogenesis and imaginal disc development. Two mutant Drosophila Ral (DRal) proteins, DRalG20V and DRalS25N, were generated and analyzed for nucleotide binding and GTPase activity. The biochemical analyses demonstrated that DRalG20V and DRalS25N act as constitutively active and dominant negative mutants, respectively. Overexpression of the wild-type DRal did not cause any visible phenotype, whereas DRalG20V and DRalS25N mutants caused defects in the development of various tissues including the cuticular surface, which is covered by parallel arrays of polarized structures such as hairs and sensory bristles. The dominant negative DRal protein caused defects in the development of hairs and bristles. These phenotypes were genetically suppressed by loss of function mutations of hemipterous and basket, encoding Drosophila Jun NH2-terminal kinase kinase (JNKK) and Jun NH2-terminal kinase (JNK), respectively. Expression of the constitutively active DRal protein caused defects in the process of dorsal closure during embryogenesis and inhibited the phosphorylation of JNK in cultured S2 cells. These results indicate that DRal regulates developmental cell shape changes through the JNK pathway.

Key Words: bristle, dorsal closure, hair, Jun NH2-terminal kinase, Ral


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