Microtubule nucleation at non-spindle pole body microtubule-organizing centers requires fission yeast centrosomin-related protein mod20p.
BACKGROUND
Many types of differentiated eukaryotic cells display microtubule distributions consistent with nucleation from noncentrosomal intracellular microtubule organizing centers (MTOCs), although such structures remain poorly characterized. In fission yeast, two types of MTOCs exist in addition to the spindle pole body, the yeast centrosome equivalent. These are the equatorial MTOC, which nucleates microtubules from the cell division site at the end of mitosis, and interphase MTOCs, which nucleate microtubules from multiple sites near the cell nucleus during interphase.


RESULTS
From an insertional mutagenesis screen we identified a novel gene, mod20+, which is required for microtubule nucleation from non-spindle pole body MTOCs in fission yeast. Mod20p is not required for intranuclear mitotic spindle assembly, although it is required for cytoplasmic astral microtubule growth during mitosis. Mod20p localizes to MTOCs throughout the cell cycle and is also dynamically distributed along microtubules themselves. We find that mod20p is required for the localization of components of the gamma-tubulin complex to non-spindle pole body MTOCs and physically interacts with the gamma-tubulin complex in vivo. Database searches reveal a family of eukaryotic proteins distantly related to mod20p; these are found in organisms ranging from fungi to mammals and include Drosophila centrosomin.


CONCLUSIONS
Mod20p appears to act by recruiting components of the gamma-tubulin complex to non-spindle pole body MTOCs. The identification of mod20p-related proteins in higher eukaryotes suggests that this may represent a general mechanism for the organization of noncentrosomal MTOCs in eukaryotic cells.
Sawin
Kenneth E
KE
Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, EH9 3JR, United Kingdom. ken.sawin@ed.ac.uk
Lourenco
Paula C C
PC
Snaith
Hilary A
HA
D000595:Amino Acid Sequence; D003080:Cold Temperature; D003593:Cytoplasm / Q000502:physiology; D005455:Fluorescent Antibody Technique; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism*; D017353:Gene Deletion; D018613:Microscopy, Confocal; D022101:Microtubule-Organizing Center / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism* / Q000502:physiology; D008969:Molecular Sequence Data; D011233:Precipitin Tests; D012568:Schizosaccharomyces; D016415:Sequence Alignment; D014404:Tubulin / Q000378:metabolism
D005656:Fungal Proteins; D014404:Tubulin