F. Delbac et al., Toxoplasma gondii myosins B/C: one gene, two tails, two localizations, anda role in parasite division, J CELL BIOL, 155(4), 2001, pp. 613-623
In apicomplexan parasites, actin-disrupting drugs and the inhibitor of myos
in heavy chain ATPase, 2,3-butanedione monoxime, have been shown to interfe
re with host cell invasion by inhibiting parasite gliding motility. We repo
rt here that the actomyosin system of Toxoplasma gondii also contributes to
the process of cell division by ensuring accurate budding of daughter cell
s. T gondii myosins B and C are encoded by alternatively spliced mRNAs and
differ only in their COOH-terminal tails. MyoB and MyoC showed distinct sub
cellular localizations and dissimilar solubilities, which were conferred by
their tails. MyoC is the first marker selectively concentrated at the ante
rior and posterior polar rings of the inner membrane complex, structures th
at play a key role in cell shape integrity during daughter cell biogenesis.
When transiently expressed, MyoB, MyoC, as well as the common motor domain
lacking the tail did not distribute evenly between daughter cells, suggest
ing some impairment in proper segregation. Stable overexpression of MyoB ca
used a significant defect in parasite cell division, leading to the formati
on of extensive residual bodies, a substantial delay in replication, and lo
ss of acute virulence in mice. Altogether, these observations suggest that
MyoB/C products play a role in proper daughter cell budding and separation.