Biology subjects

Chelaghma, S.

Publications and source records attributed to Chelaghma, S..

3 recordsLinked to original sources

bioRxiv2024

Characterisation of cell cycle checkpoint kinases in Toxoplasma gondii

Toxoplasma gondii is a protozoan parasite in the apicomplexan phylum. Apicomplexan parasites replicate using a variety of non-canonical cell division modes, distinct from binary fission, whose molecular regulation is incompletely understood. T. gondii replicates by endodyogeny in its intermediate hosts, and by endopolygeny in its definitive host. To improve our understanding of how these unusual, flexible cell division modes are regulated, we characterised the T. gondii homologues of the cell-cycle checkpoint kinases ATM and ATR. These phosphoinositol-3-kinase-like kinases are entirely absent in some related parasites including Plasmodium; in T. gondii they are present but their putative checkpoint roles were previously uncharacterised. Both TgATM and TgATR were found to be dispersed throughout the parasite, rather than restricted to the nucleus, and they did not detectably relocate to the nucleus after DNA damage. Nevertheless, they were both required for checkpoint responses to DNA damage, including acute replication slowing and phosphorylation of the DNA damage marker histone H2AX. Unusually, the two kinases seemed to cooperate in the checkpoint response, with the loss of either one largely ablating the response, regardless of the type of DNA damage. Thus, T. gondii clearly retains a DNA-damage-responsive checkpoint, but some of its key features differ from the well-studied checkpoint in human cells. AUTHOR SUMMARYToxoplasma is one of the most widespread parasites of humans, with a large proportion of the global population being infected. Infection usually causes no symptoms, but can have severe consequences in pregnant women and immunocompromised people. The Toxoplasma parasite is a single-celled organism, related to other parasites that cause important human diseases like malaria. All these parasites are distinctive in having unusual modes of replication: unlike human cells, they do not replicate by simply splitting in two. Furthermore, drugs to treat toxoplasmosis usually act to suppress the parasites replication. Therefore, it is important to understand how this unusual replication is controlled, both for our fundamental understanding of cell division modes, and to ensure effective drug treatment of toxoplasmosis. Here, we characterised for the first time the proteins that control the Toxoplasma cell cycle by responding to DNA damage. We report that a damage-responsive checkpoint exists, but has some unusual features.

microbiology↗

bioRxiv2023

Apical annuli are specialised sites of post-invasion secretion of dense granules in Toxoplasma

Apicomplexans are ubiquitous intracellular parasites of animals. These parasites use a programmed sequence of secretory events to find, invade, and then reengineer their host cells to enable parasite growth and proliferation. The secretory organelles micronemes and rhoptries mediate the first steps of invasion. Both secrete their contents through the apical complex which provides an apical opening in the parasites elaborate inner membrane complex (IMC) -- an extensive subpellicular system of flattened membrane cisternae and proteinaceous meshwork that otherwise limits access of the cytoplasm to the plasma membrane for material exchange with the cell exterior. After invasion, a second secretion programme drives host cell remodelling and occurs from dense granules. The site(s) of dense granule exocytosis, however, has been unknown. In Toxoplasma gondii, small subapical annular structures that are embedded in the IMC have been observed, but the role or significance of these apical annuli to plasma membrane function has also been unknown. Here, we determined that integral membrane proteins of the plasma membrane occur specifically at these apical annular sites, that these proteins include SNARE proteins, and that the apical annuli are sites of vesicle fusion and exocytosis. Specifically, we show that dense granules require these structures for the secretion of their cargo proteins. When secretion is perturbed at the apical annuli, parasite growth is strongly impaired. The apical annuli, therefore, represent a second type of IMC-embedded structure to the apical complex that is specialised for protein secretion, and reveal that in Toxoplasma there is a physical separation of the processes of pre- and post-invasion secretion that mediate host-parasite interactions.

cell biology↗

bioRxiv2023

Early infection response of the first trimester human placenta at single-cell scale

Placental infections are a major worldwide burden, particularly in developing countries. The placenta is a transient tissue located at the interface between the mother and the fetus. Some pathogens can access the placental barrier resulting in pathological transmission from mother to fetus, which may have a profound impact on the health of the developing fetus. Limited tissue accessibility, critical differences between humans and mice, and, until recently, lack of proper in vitro models, have hampered our understanding of the early placental response to pathogens. Here we use single-cell transcriptomics to describe the placental primary defence mechanisms against three pathogens that are known to cause fetal and maternal complications during pregnancy - Plasmodium falciparum, Listeria monocytogenes and Toxoplasma gondii. We optimise ex vivo placental explants of the first-trimester human placenta and show that trophoblasts (the epithelial-like cells of the placenta), and Hofbauer cells (placental macrophages) orchestrate a coordinated inflammatory response after 24 hours of infection. We show that hormone biosynthesis and transport are downregulated in the trophoblasts, suggesting that protective responses are promoted at the expense of decreasing other critical functions of the placenta, such as the endocrine production and the nourishment of the fetus. In addition, we pinpoint pathogen-specific effects in some placental lineages, including a strong mitochondrial alteration in the Hofbauer cells in response to T. gondii. Finally, we identify adaptive strategies and validate nutrient acquisition employed by the P. falciparum during placental malaria infection. This study provides the first detailed cellular map of the first-trimester placenta upon infection and describes the early events that may lead to fetal and placental disorders if left unchecked.

genomics↗