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Molecular and Cellular Biology, September 2001, p. 6280-6291, Vol. 21, No. 18
DBMS-CNRS UMR 50921
and DBMS-IFR 27 INSERM,2 CEA-Grenoble,
Grenoble, and CNRS UMR 7592, University of Paris VII, Jussieu,
Paris,4 France, and Biology
Department, University of California at San Diego, San Diego,
California3
Received 12 January 2001/Returned for modification 27 February
2001/Accepted 21 June 2001
Our analysis of rotund (rn) null
mutations in Drosophila melanogaster revealed that
deletion of the rn locus affects both spermatid and
retinal differentiation. In the male reproductive system, the absence
of RnRacGAP induced small testes, empty seminal vesicles, short
testicular cysts, reduced amounts of interspermatid membrane, the absence of individualization complexes, and
incomplete mitochondrial condensation. Flagellar growth
continued within the short rn null cysts to produce
large bulbous terminations of intertwined mature flagella.
Organization of the retina was also severely perturbed as evidenced
by grossly misshapen ommatidia containing reduced numbers of
photoreceptor and pigment cells. These morphological phenotypes were
rescued by genomic rnRacGAP transgenes, demonstrating that RnRacGAP function is critical to spermatid and retinal differentiation. The testicular
phenotypes were suppressed by heterozygous hypomorphic mutations in the
Dras1 and drk genes, indicating
cross talk between RacGAP-regulated signaling and that of the Ras
pathway. The observed genetic interactions are consistent
with a model in which Rac signaling is activated by Ras and
negatively regulated by RnRacGAP during spermatid differentiation. RnRacGAP and Ras cross talk also operated during retinal
differentiation; however, while the heterozygous hypomorphic
drk mutation continued to act as a
suppressor of the rn null mutation, the
heterozygous hypomorphic Dras1 mutation induced novel
retinal phenotypes.
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.18.6280-6291.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
RotundRacGAP Functions with Ras during Spermatogenesis and
Retinal Differentiation in Drosophila
melanogaster

and
*
Corresponding author. Mailing address: DBMS-CNRS
UMR 5092, CEA-Grenoble, 17 Rue des Martyrs, F-38054 Grenoble Cedex
9, France. Phone: 33-4-38-78-30-90. Fax: 33-4-38-78-51-85. E-mail: ruth.griffin-shea{at}cea.fr.
Present address: CNRS-CERMAV, 38041 Grenoble Cedex 9, France.
Present address: ENSAR-INRA, Laboratoire Ecologie et Sciences
Phytosanitaires, CS 84215, F-35042 Rennes Cedex, France.
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