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General Comment |
Geles KG, et al reported a Role for Caenorhabditis elegans Importin IMA-2 in Germ Line
and Embryonic Mitosis.
The importin alpha family of nuclear-cytoplasmic transport factors mediates the
nuclear localization of proteins containing classical nuclear localization signals.
Metazoan animals express multiple importin alpha proteins, suggesting their possible
roles in cell differentiation and development. Adult Caenorhabditis elegans
hermaphrodites express three importin alpha 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.
Thus, 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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