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Grech, J.

Publications and source records attributed to Grech, J..

2 recordsLinked to original sources
bioRxiv2021

Malaria transmission relies on concavin-mediated maintenance of Plasmodium sporozoite cell shape

During transmission of malaria-causing parasites from mosquitoes to mammals, Plasmodium sporozoites migrate rapidly in the skin to search for a blood vessel. The high migratory speed and narrow passages taken by the parasites suggest considerable strain on the sporozoites to maintain their shape. Here we report on a newly identified protein, concavin, that is important for maintenance of the sporozoite shape inside salivary glands of mosquitoes and during migration in the skin. Concavin-GFP localized at the cytoplasmic periphery of sporozoites and concavin(-) sporozoites progressively rounded up upon entry of salivary glands. These rounded concavin(-) sporozoites failed to pass through the narrow salivary ducts and were hence rarely ejected by mosquitoes. However, normally shaped concavin(-) sporozoites could be transmitted and migrated in the skin or skin like environments. Strikingly, motile concavin(-) sporozoites could disintegrate while migrating through narrow strictures in the skin leading to parasite arrest or death and decreased transmission efficiency. We suggest that concavin contributes to cell shape maintenance by riveting the plasma membrane to the subtending inner membrane complex. SIGNIFICANCEMalaria parasites are transmitted by Anopheles mosquitoes and rely on rapid migration for establishing an infection. We identified and characterized a protein, named concavin, essential for maintaining the shape of the sporozoite. Concavin is a membrane associated protein facing the cytoplasm suggesting that it contributes to riveting the plasma membrane to the subtending inner membrane complex. Sporozoites lacking concavin can round up in the salivary glands, are less well transmitted to mice and disintegrate while migrating in the skin. Hence, concavin is essential for parasite transmission and infectivity. Highlights- A membrane associated protein is essential for Plasmodium shape maintenance -Migrating parasites disintegrate in the absence of concavin -First protein essential for cellular integrity of Plasmodium sporozoites -Thickened and deformed Plasmodium sporozoites fail to be transmitted by mosquitoes

microbiology↗
bioRxiv2021

A phenotypic screen using splitCas9 identifies essential genes required for actin regulation during host cell egress and invasion by Toxoplasma gondii

Apicomplexan parasites, such as Toxoplasma gondii, possess unique organelles, cytoskeletal structures, signalling cascades, replicate by internal budding within a specialised compartment and actively invade and exit the host cell, to name a few aspects of the unique biology that characterise this phylum. Due to their huge phylogenetic distance from well established model organisms, such as opisthokonts, comparative genomics has a limited capacity to infer gene functions and conserved proteins can fulfil different roles in apicomplexans. Indeed, approximately 30% of all genes are annotated as hypothetical and many had a crucial role during the asexual life cycle in genome-wide screens. While the current CRISPR/Cas9-based screens allow the identification of fitness conferring genes, only little information about the respective functions can be obtained. To overcome this limitation, and to group genes of interest into functional groups, we established a conditional Cas9-system in T. gondii that allows phenotypic screens. Using an indicator strain for F-actin dynamics and apicoplast segregation, we identified critical genes required for defined steps during the asexual life cycle. The detailed characterisation of two of these candidates revealed them to be critical for host cell egress and invasion and to act at different time points in the disassembly of the intravacuolar F-actin network. While the signalling linking factor (SLF) is an integral part of a signalling complex required for early induction of egress, a novel conoid protein (conoid gliding protein, CGP) acts late during egress and is required for the activation of gliding motility.

microbiology↗