ApiLoc - A database of published protein sub-cellular localisation in Apicomplexa

version 3 (curated until May 28, 2011)

Disruption of microtubules uncouples budding and nuclear division in Toxoplasma gondii.

Morrissette, N. S., Sibley, L. D. (2002 Mar 1, J Cell Sci)

The tachyzoite stage of the protozoan parasite Toxoplasma gondii has two populations of microtubules: spindle microtubules and subpellicular microtubules. To determine how these two microtubule populations are regulated, we investigated microtubule behavior during the cell cycle following treatment with microtubule-disrupting drugs. Previous work had established that the microtubule populations are individually nucleated by two distinct microtubule-organizing centers (MTOCs): the apical polar ring for the subpellicular microtubules and spindle pole plaques/centrioles for the spindle microtubules. When replicating tachyzoites were treated with 0.5 microM oryzalin or 1.0 mM colchicine they retained the capacity to form a spindle and undergo nuclear division. Although these parasites could complete budding, they lost the bulk of their subpellicular microtubules and the ability to reinvade host cells. Both nascent spindle and subpellicular microtubules were disrupted in 2.5 microM oryzalin or 5.0 mM colchicine. Under these conditions, parasites grew in size and replicated their genome but were incapable of nuclear division. After removal from 0.5 microM oryzalin, Toxoplasma tachyzoites were able to restore normal subpellicular microtubules and a fully invasive phenotype. When oryzalin was removed from Toxoplasma tachyzoites treated with 2.5 microM drug, the parasites attempted to bud as crescent-shaped tachyzoites. Because the polyploid nuclear mass could not be correctly segregated, many daughter parasites lacked nuclei altogether although budding and scission from the maternal mass was able to be completed. Multiple MTOCs permit Toxoplasma tachyzoites to control nuclear division independently from cell polarity and cytokinesis. This unusual situation grants greater cell cycle flexibility to these parasites but abolishes the checks for coregulation of nuclear division and cytokinesis found in other eukaryotes.

PubMed: 11870220, full text

Localisation information

TGME49_031640 (IMC1, ALV1, IMC, NET1) membrane skeletal protein IMC1

Experimental localisation: inner membrane complex during intracellular tachyzoite, not residual body during intracellular tachyzoite
  • Species: Toxoplasma gondii
  • Quote inferring localisation: "In order to distinguish daughter parasites from the residual body, we used an antibody (45.15, anti-IMC-1) that recognizes an intermediate-filament-like component of a network that is associated with the inner membrane complex (IMC). In untreated tachyzoites, IMC-1 labeling was localized directly below the plasma membrane and ran from a region directly under the extreme apex of the parasite to a region close to the posterior of the tachyzoite (Fig. 4A, top row). It began in a region coincident with the subpellicular microtubules but extended significantly beyond them. The residual body was not labeled with the IMC-1 antibody."
  • Microscopy type: Light, EM
  • Microscopy method: Monoclonal antibody directly to protein
  • Strain: RH
  • Gene model mapping comments: inferred from another publication
  • Localisation record: IMC and not residual body during intracellular tachyzoite

TGME49_047230 (centrin) caltractin (centrin), putative

Experimental localisation: centriole during intracellular tachyzoite
  • Species: Toxoplasma gondii
  • Quote inferring localisation: "Toxoplasma centrioles were separated within G1/S phase transition (at the time of thymidine release, not shown). In replicating parasites (from 1 to 4 hours after release), the spindle microtubules (labeled with tubulin) are found in close proximity to the centrioles (labeled with centrin; Fig. 2B)."
  • Microscopy type: Light
  • Microscopy method: Monoclonal antibody directly to protein
  • Strain: RH
  • Gene model mapping comments: inferred from another publication
  • Localisation record: centriole during intracellular tachyzoite