Moesin controls cortical rigidity, cell rounding, and spindle morphogenesis during mitosis.
BACKGROUND
During mitosis, animal cells undergo a complex sequence of morphological changes, from retraction of the cell margin and cell rounding at the onset of mitosis to axial elongation and cytokinesis at mitotic exit. The molecular mechanisms driving the early changes in mitotic cell form and their functional significance, however, remain unknown. Here we identify Moesin as a key player. Moesin is the sole Drosophila member of the ERM proteins, which, once activated via phosphorylation, crosslink actin filaments to the cytoplasmic tails of plasma membrane proteins.


RESULTS
We find that the Moesin is activated upon entry into mitosis, is necessary for the accompanying increase in cortical rigidity and cell rounding and, when artificially activated, is sufficient to induce both processes in interphase cells, independently of Myosin II. This phospho-Moesin-induced increase in cortical rigidity plays an important role during mitotic progression, because spindle morphogenesis and chromosome alignment are compromised in Moesin RNAi cells. Significantly, however, the spindle defects observed in soft metaphase cells can be rescued by the re-establishment of cortical tension from outside the cell.


CONCLUSIONS
These data show that changes in the activity and localization of Moesin that accompany mitotic progression contribute to the establishment of a stiff, rounded cortex at metaphase and to polar relaxation at anaphase and reveal the importance of this Moesin-induced increase in cortical rigidity for spindle morphogenesis and orderly chromosome segregation. In doing so, they help to explain why dynamic changes in cortical architecture are a universal feature of mitosis in animal cells.
Kunda
Patricia
P
MRC Laboratory of Molecular Cell Biology, UCL, Gower Street, London WC1E 6BT, United Kingdom.
Pelling
Andrew E
AE
Liu
Tao
T
Baum
Buzz
B
D000199:Actins / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D048430:Cell Shape / Q000502:physiology*; D020090:Chromosome Segregation / Q000502:physiology*; D029721:Drosophila Proteins / Q000378:metabolism; D007399:Interphase / Q000502:physiology; D008840:Microfilament Proteins / Q000378:metabolism*; D008938:Mitosis / Q000502:physiology*; D024462:Myosin Type II / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D008941:Spindle Apparatus / Q000378:metabolism*; D013997:Time Factors
D000199:Actins; D029721:Drosophila Proteins; D008840:Microfilament Proteins; C071058:moesin; D017346:Protein Serine-Threonine Kinases; C492662:Slik protein, Drosophila; D024462:Myosin Type II