title: Inner nuclear membrane protein Ima1 is dispensable for intranuclear positioning of centromeres.
abstract: Inner nuclear membrane (INM) proteins play a role in spatial organization of chromosomes within the nucleus. In the fission yeast Schizosaccharomyces pombe, Sad1, an INM protein of the conserved SUN-domain family, plays an active role in moving chromosomes along the nuclear membranes during meiotic prophase. Ima1 is another conserved INM protein recently identified. A previous study claimed that Ima1 is essential for mitotic cell growth, linking centromeric heterochromatin to the spindle-pole body. However, we obtained results contradictory to the previously proposed role for Ima1: Ima1 was dispensable for mitotic cell growth or centromere positioning. This discrepancy was attributed to incorrect ima1 deletion mutants used in the previous study. Our results show that Ima1 collaborates with two other conserved INM proteins of the LEM-domain family that are homologous to human Man1 and Lem2. Loss of any one of three INM proteins has no effect on mitotic cell growth; however, loss of all these proteins causes severe defects in mitotic cell growth and nuclear membrane morphology. Considering that all three INM proteins interact with Sad1, these results suggest that Ima1, Lem2 and Man1 play at least partially redundant roles for nuclear membrane organization.
authors: Graduate School of Frontier Biosciences, Osaka University, Yamadaoka, Suita, Japan. hiraoka@fbs.osaka-u.ac.jp
authors: Yasushi
authors: Y
authors: Hiraoka
authors: Hiromi
authors: H
authors: Maekawa
authors: Haruhiko
authors: H
authors: Asakawa
authors: Yuji
authors: Y
authors: Chikashige
authors: Tomoko
authors: T
authors: Kojidani
authors: Hiroko
authors: H
authors: Osakada
authors: Atsushi
authors: A
authors: Matsuda
authors: Tokuko
authors: T
authors: Haraguchi
mesh_terms: D002503:Centromere / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D008938:Mitosis; D009685:Nuclear Envelope / Q000378:metabolism / Q000648:ultrastructure; D034881:Nuclear Lamina / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D021381:Protein Transport; D012568:Schizosaccharomyces / Q000378:metabolism / Q000648:ultrastructure; D029702:Schizosaccharomyces pombe Proteins / Q000378:metabolism*; D008941:Spindle Apparatus / Q000378:metabolism
chemical_list: C569257:Ima1 protein, S pombe; D008565:Membrane Proteins; D009687:Nuclear Proteins; D029702:Schizosaccharomyces pombe Proteins