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Vol. 13, Issue 9, 3138-3147, September 2002

A Role for Caenorhabditis elegans Importin IMA-2 in Germ Line and Embryonic Mitosis

Kenneth G. Geles,^* Jeffrey J. Johnson, Sena Jong, and Stephen A. Adam

Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611

The importin  family of nuclear-cytoplasmic transport factors mediates the nuclear localization of proteins containing classical nuclear localization signals. Metazoan animals express multiple importin  proteins, suggesting their possible roles in cell differentiation and development. Adult Caenorhabditis elegans hermaphrodites express three importin  proteins, IMA-1, IMA-2, and IMA-3, each with a distinct expression and localization pattern. IMA-2 was expressed exclusively in germ line cells from the early embryonic through adult stages. The protein has a dynamic pattern of localization dependent on the stage of the cell cycle. In interphase germ cells and embryonic cells, IMA-2 is cytoplasmic and nuclear envelope associated, whereas in developing oocytes, the protein is cytoplasmic and intranuclear. During mitosis in germ line cells and embryos, IMA-2 surrounded the condensed chromosomes but was not directly associated with the mitotic spindle. The timing of IMA-2 nuclear localization suggested that the protein surrounded the chromosomes after fenestration of the nuclear envelope in prometaphase. Depletion of IMA-2 by RNA-mediated gene interference (RNAi) resulted in embryonic lethality and a terminal aneuploid phenotype. ima-2(RNAi) embryos have severe defects in nuclear envelope formation, accumulating nucleoporins and lamin in the cytoplasm. We conclude that IMA-2 is required for proper chromosome dynamics in germ line and early embryonic mitosis and is involved in nuclear envelope assembly at the conclusion of mitosis.

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Corresponding author. E-mail address: s-adam{at}northwestern.edu.

Present addresses: ^*Department of Molecular and Cell Biology, 401 Barker Hall, #3204, University of California, Berkeley, Berkeley, CA 94720-3204; Akceli, Inc., 1 Hampshire St., Cambridge, Massachusetts 02139.

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Molecular Biology of the Cell
Vol. 13, 3138-3147, September 2002
Copyright © 2002 by The American Society for Cell Biology

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