XRHAMM functions in ran-dependent microtubule nucleation and pole formation during anastral spindle assembly.
BACKGROUND
The regulated assembly of microtubules is essential for bipolar spindle formation. Depending on cell type, microtubules nucleate through two different pathways: centrosome-driven or chromatin-driven. The chromatin-driven pathway dominates in cells lacking centrosomes.


RESULTS
Human RHAMM (receptor for hyaluronic-acid-mediated motility) was originally implicated in hyaluronic-acid-induced motility but has since been shown to associate with centrosomes and play a role in astral spindle pole integrity in mitotic systems. We have identified the Xenopus ortholog of human RHAMM as a microtubule-associated protein that plays a role in focusing spindle poles and is essential for efficient microtubule nucleation during spindle assembly without centrosomes. XRHAMM associates both with gamma-TuRC, a complex required for microtubule nucleation and with TPX2, a protein required for microtubule nucleation and spindle pole organization.


CONCLUSIONS
XRHAMM facilitates Ran-dependent, chromatin-driven nucleation in a process that may require coordinate activation of TPX2 and gamma-TuRC.
Groen
Aaron C
AC
Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA. aaron_groen@students.hms.harvard.edu
Cameron
Lisa A
LA
Coughlin
Margaret
M
Miyamoto
David T
DT
Mitchison
Timothy J
TJ
Ohi
Ryoma
R
D000818:Animals; D001483:Base Sequence; D018797:Cell Cycle Proteins / Q000378:metabolism; D018385:Centrosome / Q000378:metabolism*; D002853:Chromatography, Liquid; D017931:DNA Primers; D005455:Fluorescent Antibody Technique; D015151:Immunoblotting; D013058:Mass Spectrometry; D008869:Microtubule-Associated Proteins / Q000235:genetics* / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism*; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D017422:Sequence Analysis, DNA; D008941:Spindle Apparatus / Q000378:metabolism*; D014981:Xenopus; D029867:Xenopus Proteins / Q000378:metabolism; D020931:ran GTP-Binding Protein / Q000378:metabolism
D018797:Cell Cycle Proteins; D017931:DNA Primers; C000623051:Hmmr protein, Xenopus; D008869:Microtubule-Associated Proteins; C489079:NUMA1 protein, Xenopus; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D010750:Phosphoproteins; C486551:TPX2 protein, Xenopus; D029867:Xenopus Proteins; D020931:ran GTP-Binding Protein