On 2013 Sep 26, Markus Meissner commented:

Dr Clare Harding (Meissner group):

This study by Farrell and Gubbels continues this group’s work in understanding the unusual method of cell division in Toxoplasma gondii, specifically the role of the kinetochore, a complex of proteins used to attach the centromere to the spindle fibres in mitosis. In Toxoplasma, unlike in mammalian systems, there is now convincing evidence that chromosomes remain attached to the spindle core throughout the cell cycle. This suggests that the kinetochore could be dispensable in Toxoplasma replication. The authors demonstrate that two conserved kinetochore proteins, TgNuf2 and TgNdc80, remain associated with the spindle core throughout the cell cycle in Toxoplasma. Although ablation of microtubules resulted in a partial disruption of kinetochore clustering, microtubules were not absolutely required for this localisation. Interestingly, conditional knock-down of TgNuf2 resulted in a complete inability of the parasites to grow. As predicted from other organisms, a reduction of TgNuf2 resulted in chromosome miss-segregation.<br> Knock-down of TgNuf2 resulted in simultaneous depletion of TgNdc80. This suggests these proteins form a stable dimer, which has been demonstrated using human proteins however remains to be confirmed in Toxoplasma. However, depletion of both proteins complicates the picture with regards to the phenotype observed. The authors were unable to identify any other components of the kinetochore through homology to other organisms and several key components of these pathways appear to be missing in Toxoplasma. In order to fully understand the role of the kinetochore in Toxoplasma cell division, more components of the kinetochore need to be identified, potentially using a pull-down approach. The identification of a putative novel nuclear localisation signal (NLS) for apicomplexan parasites is potentially interesting and the authors have demonstrated that this sequence is important for the localisation of TgNuf2. However, as the authors mention, it is possible that this domain is required for the structural integrity of the protein; hopefully future studies will address this issue in more depth.<br> Overall, this is a very interesting paper which significantly adds to our knowledge of the molecular mechanisms of cell division in this apicomplexan parasite.

On 2013 Sep 26, Markus Meissner commented:

Dr Clare Harding (Meissner group):

This study by Farrell and Gubbels continues this group’s work in understanding the unusual method of cell division in Toxoplasma gondii, specifically the role of the kinetochore, a complex of proteins used to attach the centromere to the spindle fibres in mitosis. In Toxoplasma, unlike in mammalian systems, there is now convincing evidence that chromosomes remain attached to the spindle core throughout the cell cycle. This suggests that the kinetochore could be dispensable in Toxoplasma replication. The authors demonstrate that two conserved kinetochore proteins, TgNuf2 and TgNdc80, remain associated with the spindle core throughout the cell cycle in Toxoplasma. Although ablation of microtubules resulted in a partial disruption of kinetochore clustering, microtubules were not absolutely required for this localisation. Interestingly, conditional knock-down of TgNuf2 resulted in a complete inability of the parasites to grow. As predicted from other organisms, a reduction of TgNuf2 resulted in chromosome miss-segregation.<br> Knock-down of TgNuf2 resulted in simultaneous depletion of TgNdc80. This suggests these proteins form a stable dimer, which has been demonstrated using human proteins however remains to be confirmed in Toxoplasma. However, depletion of both proteins complicates the picture with regards to the phenotype observed. The authors were unable to identify any other components of the kinetochore through homology to other organisms and several key components of these pathways appear to be missing in Toxoplasma. In order to fully understand the role of the kinetochore in Toxoplasma cell division, more components of the kinetochore need to be identified, potentially using a pull-down approach. The identification of a putative novel nuclear localisation signal (NLS) for apicomplexan parasites is potentially interesting and the authors have demonstrated that this sequence is important for the localisation of TgNuf2. However, as the authors mention, it is possible that this domain is required for the structural integrity of the protein; hopefully future studies will address this issue in more depth.<br> Overall, this is a very interesting paper which significantly adds to our knowledge of the molecular mechanisms of cell division in this apicomplexan parasite.