A coiled-coil protein is required for coordination of karyokinesis and cytokinesis in Toxoplasma gondii

Abstract

Toxoplasma gondii is a unicellular eukaryotic pathogen that belongs to the Apicomplexa phylum, which encompasses some of the deadliest pathogens of medical and veterinary importance. The centrosome is key to the organisation and coordination of the cell cycle and division of apicomplexan parasites. The T. gondii centrosome possesses a particular bipartite structure (outer and inner cores). One of the main roles of the centrosome is to ensure proper coordination of karyokinesis. However, how these 2 events are coordinated is still unknown in T. gondii, for which the centrosome components are poorly described. To gain more insights into the biology and the composition of the T. gondii centrosome, we characterised a protein that resides at the interface of the outer and inner core centrosomes. TgCep530 is a large coiled-coil protein with an essential role in the survival of the parasite. Depletion of this protein leads to the accumulation of parasites lacking nuclei and disruption of the normal cell cycle. Lack of TgCep530 results in a discoordination between the nuclear cycle and the budding cycle that yields fully formed parasites without nuclei. TgCep530 has a crucial role in the coordination of karyokinesis and cytokinesis.

Apicomplexa Cell Cycles: Something Old, Borrowed, Lost, and New

“…The inner and outer cores of the tachyzoite centrosome function and duplicate independently and may have distinct evolutionary history. The inner core is copied after the outer core in S phase ( Figure 2 ), and contains orthologs of the coiled-coiled centrosomal proteins of higher eukaryotes, while lacking centrin [ 13 , 27 ]. Functionally, the inner core is required for chromosome replication in the tachyzoite [ 13 , 28 ], and in genetic mutants that over-duplicate the inner core the centrocone is also over duplicated [ 13 ].…”

TgCep250 is dynamically processed through the division cycle and essential for structural integrity of the Toxoplasma centrosome

“…Overduplication of outer-cores has been reported in parasites expressing a temperature sensitive allele of PCM component MAPK-L1 7 , whereas outer-core fragmentation was observed in TgCep530 depleted parasites 8 . In TgCep250 depleted cells we observed multiple outer-cores, which could either be the result of overduplication or fragmentation (Fig.…”

“…Orthologs of many key components in the mammalian centrosome cannot be found in the Toxoplasma genome 6 . Even without canonical protein orthologs, recent studies have shown that a group of coiled-coil proteins localize to the centrosome and support proper karyokinesis and cytokinesis 7–8 . This work identified a distinctive architecture of two centrosome cores: the outer-core (distal to the nucleus) and the inner-core (proximal to the nucleus).…”

A single master regulator controls asexual cell cycle division patterns inToxoplasma gondii

“…Although expression of the SFA fibers or other known centrosome markers were unaffected in the mutant, we noticed that the expression of a key centrosomal protein, TgCep530, was directly under the control of TgAP2IX-5 (downregulated in RNA-seq and its promoter bound in ChIP-seq). This protein was shown to be targeted to a centrosomal region situated between the inner and outer core [29]. It is essential for the coordination of the nuclear and budding cycle although budding seemed to occur [29].…”

“…This protein was shown to be targeted to a centrosomal region situated between the inner and outer core [29]. It is essential for the coordination of the nuclear and budding cycle although budding seemed to occur [29]. However, its depletion leads to the accumulation of outer core centrosome [29], a phenotype that is not observed with TgAP2IX-5 expression.…”