Suvorova ES, Francia M, Striepen B, White MW. A novel bipartite centrosome coordinates the apicomplexan cell cycle.
PLoS Biol 2015;
13:e1002093. [PMID:
25734885 PMCID:
PMC4348508 DOI:
10.1371/journal.pbio.1002093]
[Citation(s) in RCA: 88] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2014] [Accepted: 01/30/2015] [Indexed: 12/11/2022] Open
Abstract
Apicomplexan parasites can change fundamental features of cell division during their life cycles, suspending cytokinesis when needed and changing proliferative scale in different hosts and tissues. The structural and molecular basis for this remarkable cell cycle flexibility is not fully understood, although the centrosome serves a key role in determining when and how much replication will occur. Here we describe the discovery of multiple replicating core complexes with distinct protein composition and function in the centrosome of Toxoplasma gondii. An outer core complex distal from the nucleus contains the TgCentrin1/TgSfi1 protein pair, along with the cartwheel protein TgSas-6 and a novel Aurora-related kinase, while an inner core closely aligned with the unique spindle pole (centrocone) holds distant orthologs of the CEP250/C-Nap protein family. This outer/inner spatial relationship of centrosome cores is maintained throughout the cell cycle. When in metaphase, the duplicated cores align to opposite sides of the kinetochores in a linear array. As parasites transition into S phase, the cores sequentially duplicate, outer core first and inner core second, ensuring that each daughter parasite inherits one copy of each type of centrosome core. A key serine/threonine kinase distantly related to the MAPK family is localized to the centrosome, where it restricts core duplication to once per cycle and ensures the proper formation of new daughter parasites. Genetic analysis of the outer core in a temperature-sensitive mutant demonstrated this core functions primarily in cytokinesis. An inhibition of ts-TgSfi1 function at high temperature caused the loss of outer cores and a severe block to budding, while at the same time the inner core amplified along with the unique spindle pole, indicating the inner core and spindle pole are independent and co-regulated. The discovery of a novel bipartite organization in the parasite centrosome that segregates the functions of karyokinesis and cytokinesis provides an explanation for how cell cycle flexibility is achieved in apicomplexan life cycles.
The apicomplexan parasite Toxoplasma gondii has a unique centrosome with two specialized compartments, potentially explaining the remarkable flexibility in life cycle that these organisms can show in diverse host cells.
Apicomplexan parasites infect many different hosts and tissues, causing numerous human diseases, including malaria. These important pathogens have a peculiar cell cycle in which chromosomes sometimes amplify to remarkable levels, followed by concerted cell division—providing an unusual proliferative capacity. This capacity for proliferation, combined with an ability to change the scale of replication when needed, are hallmarks of the cell cycles of these parasites. Yet the molecular mechanism responsible for these peculiar cell cycles remains one of the unsolved mysteries of Apicomplexa biology. Here we show that the centrosome—an organelle that orchestrates several aspects of the cell cycle—of the apicomplexan parasite Toxoplasma gondii contains specialized structures that coordinate parasite cell division. Our findings demonstrate that a two-part centrosomal architecture, comprising an inner and an outer core with distinct protein compositions, segregates the processes of mitosis from the assembly of new daughter parasites. The modular organization of the centrosome offers an explanation for how cell division can be suspended while the parasites amplify their genome to the biotic scale required for their life cycles. It is unknown whether these distinct centrosome core complexes evolved independently in Apicompexa. Another possibility is that the foundations for these mechanisms were present in the original eukaryote, which could explain how the distinct extranuclear centrosome of animal cells and the novel yeast spindle pole body of the nuclear envelope may have evolved from a common ancestor.
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