Originally published as Genetics Published Articles Ahead of Print on February 1, 2008.

Genetics, Vol. 178, 839-850, February 2008, Copyright © 2008
doi:10.1534/genetics.107.081778

Drosophila Importin 1 Performs Paralog-Specific Functions Essential For Gametogenesis

R. Ratan^*,1, D. A. Mason^,1,2, B. Sinnot^*, D. S. Goldfarb^,3 and R. J. Fleming^*

^* Biology Department, Trinity College, Hartford, Connecticut 06106 and Department of Biology, University of Rochester, Rochester, New York 14627

³ Corresponding author: Department of Biology, 436 Hutchison Hall, University of Rochester, Rochester, NY 14627.
E-mail: dasg{at}mail.rochester.edu

Importin 's mediate nuclear transport by linking nuclear localization signal (NLS)-containing proteins to importin β1. Animal genomes encode three conserved groups of importin 's, 1's, 2's, and 3's, each of which are competent to bind classical NLS sequences. Using Drosophila melanogaster we describe the isolation and phenotypic characterization of the first animal importin 1 mutant. Animal 1's are more similar to ancestral plant and fungal 1-like genes than to animal 2 and 3 genes. Male and female importin 1 (D1) null flies developed normally to adulthood (with a minor wing defect) but were sterile with defects in gametogenesis. The D1 mutant phenotypes were rescued by D1 transgenes, but not by D2 or D3 transgenes. Genetic interactions between the ectopic expression of D1 and the karyopherins CAS and importin β1 suggest that high nuclear levels of D1 are deleterious. We conclude that D1 performs paralog-specific activities that are essential for gametogenesis and that regulation of subcellular D1 localization may affect cell fate decisions. The initial expansion and specialization of the animal importin -gene family may have been driven by the specialized needs of gametogenesis. These results provide a framework for studies of the more complex mammalian importin -gene family.

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