Biology subjects

Gubbels, M.-J.

Publications and source records attributed to Gubbels, M.-J..

3 recordsLinked to original sources

bioRxiv2018

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

The Toxoplasma centrosome is a unique bipartite structure comprising an inner- and outer-core responsible for the nuclear cycle (mitosis) and budding cycles (cytokinesis), respectively. These two cores remain associated during the cell cycle but have been proposed to function independently. Here, we describe the function of a large coiled-coil protein, TgCep250, in connecting the two centrosomal cores and promoting their structural integrity. Throughout the cell cycle TgCep250 localizes to the centrosome inner-core but resides on both inner- and outer-cores during the onset of cell division. This dynamic localization pattern is associated with proteolysis: the processed version residing on the inner-core. In the absence of TgCep250, stray centrosome inner- and outer-core foci were observed; detachment of the inner-outer-core connection resulted in nuclear partitioning defects. The detachment between centrosome inner- and outer-core was found in only one of the centrosomes during cell division, indicating distinct states of mother and daughter centrosomes. We further dissected the hierarchical organization of centrosome and kinetochore complex through depletion of kinetochore component TgNuf2, which resulted in dissociation of the intact bipolar centrosome from the nuclear periphery. Together, these data suggest that TgCep250 bridges the interaction between the centrosome cores but not between the inner-core and kinetochore.\n\nShort SummaryThe opportunistic apicomplexan parasite Toxoplasma gondii uses a bipartite centrosome to independently regulate mitosis and cytokinesis. Here we report a large coiled-coil protein that functions to integrate the two centrosomal cores for faithful cell division. This study also reveals the layered structural organization of the centrosome/kinetochore complex.

microbiology↗

bioRxiv2018

A member of the ferlin calcium sensor family is essential for Toxoplasma gondii rhoptry secretion

Invasion of host cells by apicomplexan parasites such as Toxoplasma gondii is critical for their infectivity and pathogenesis. In Toxoplasma, secretion of essential egress, motility and invasion-related proteins from microneme organelles is regulated by oscillations of intracellular Ca2+. Later stages of invasion are considered Ca2+-independent, including the secretion of proteins required for host cell entry and remodeling from the parasites rhoptries. We identified a family of three Toxoplasma proteins with homology to the ferlin family of double C2 domain-containing Ca2+ sensors. In humans and model organisms such Ca2+ sensors orchestrate Ca2+-dependent exocytic membrane fusion with the plasma membrane. One ferlin that is conserved across the Apicomplexa, TgFER2, localizes to the parasites cortical membrane skeleton, apical end, and rhoptries. Unexpectedly, conditionally TgFER2-depleted parasites secreted their micronemes normally and were completely motile. However, these parasites were unable to invade host cells and were therefore not viable. Specifically, knockdown of TgFER2 prevented rhoptry secretion and these parasites failed to form the moving junction on the parasite-host interface necessary for host cell invasion. Collectively, these data demonstrate that the putative Ca2+ sensor TgFER2 is required for the secretion of rhoptries. These findings provide the first regulatory and mechanistic insights into this critical yet poorly understood aspect of apicomplexan host cell invasion.\n\nGraphical abstract\n\nO_FIG O_LINKSMALLFIG WIDTH=199 HEIGHT=200 SRC=\"FIGDIR/small/304048_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (58K):\norg.highwire.dtl.DTLVardef@505202org.highwire.dtl.DTLVardef@138400aorg.highwire.dtl.DTLVardef@1f468beorg.highwire.dtl.DTLVardef@1089d34_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2017

Two phosphoglucomutase paralogs regulate triggered secretion of the Toxoplasma micronemes

Parafusin is a phosphoglucomutase (PGM) paralog that acts as a signaling scaffold protein in calcium mediated exocytosis across many eukaryotes. In Toxoplasma gondii the parafusin related protein 1 (PRP1) has been associated in indirect and heterologous studies with the regulated exocytosis of the micronemes, which are required for successful host cell invasion and egress. Here we directly assessed the role of PRP1 by deleting the gene from the parasite. We observed a specific defect in microneme secretion in response to high Ca2+ fluxes, but not to phosphatidic acid fluxes controlling microneme release. We observed no defect in constitutive microneme secretion which was sufficient to support completion of the lytic cycle. Furthermore, deletion of the other PGM in Toxoplasma, PGM2, as well as the double PRP1/PGM2 deletion resulted in a similar phenotype. This suggests a functional interaction between these two genes. Strikingly, tachyzoites without both paralogs are completely viable in vitro and during acute mice infections. This indicates that PGM activity is neither required for glycolysis. In conclusion, the PRP1-PGM2 pair is required for a burst in microneme secretion upon high Ca2+ fluxes, but this burst is not essential to complete the lytic cycle of the parasite.\n\nPlain Language SummaryCalcium mediated control of microneme secretion is essential for host cell invasion and egress of Toxoplasma gondii. Here it is shown that the two phosphoglucomutases in Toxoplasma both function in the translation of a spike in calcium into a burst in microneme secretion.

microbiology↗