Description
Title: "The mystery of rhoptry secretion in Toxoplasma gondii ”
Speaker: 
Maryse Lebrun, PhD
Director of Research, CNRS, University of Montpellier, France
Abstract:
To invade and replicate within their hosts, apicomplexan parasites secrete and inject the content of an organelle called rhoptry into the host cell. The mechanism by which rhoptries are discharged is unclear and appears distinct from those in bacteria, yeast, animals and plants. We first combined decades-old pioneering ultrastructural observations in Apicomplexa, with data on regulated secretion from their free-living relatives belonging to the Ciliata group, and uncovered proteins implicated in rhoptry exocytosis in Toxoplasma gondii and Plasmodium falciparum. Exocytosis of rhoptries depends on intramembranous particles arranged in the shape of a rosette embedded into the plasma membrane at the parasite apex, and visible by freeze-fracture. In situ cryo-electron tomography (cryo-ET) showed that the rosette is part of an elaborate structure named the Rhoptry Secretory Apparatus, which represents a unique eukaryotic secretory machinery. In addition, we further extended the use of ciliate models, and performed a Tetrahymena-based transcriptomic screen to uncover novel exocytic factors in Ciliata, with conserved functions in Apicomplexa. Our results showed a common ancestry for the exocytosis of regulated-secretory organelles in two groups of protists that diverged hundreds of millions of years ago and have adopted radically different lifestyles
Bio:
I have experience (over 20 years) in parasite molecular and cellular biology. I have studied microbiology and cell biology in Rennes (France). I was trained in microbiology at the “Institut de la Recherche Agronomique” (INRA) in Tours, and learned bacteriology, cellular microbiology and genetics from Pascale Cossart at the Institut Pasteur in Paris. I then moved on parasitology motivated by the fascinating and unique invasion process of Apicomplexa. In the past 20 years I have pursued studies to understand the cell biology of apicomplexan parasites (mostlyToxoplasma and more recently Plasmodium). Most of these studies were rooted in genetic, molecular and cellular approaches. I contributed to the understanding of the functions of secretory organelles in Toxoplasma, in particular in the formation of the “moving junction” (MJ), a key structure devoted for invasion. I also contributed in our understanding of the mechanisms of targeting proteins to secretory organelles and of the molecular mechanisms to build secretory organelles. My laboratory has recently started a new project to solve the mechanism of exocytosis of the secretory organelles called rhoptry, which was a long-standing conundrum of the cell biology of apicomplexan parasites. Based on comparative observations between Apicomplexa and Ciliates we demonstrated the existence of a common ancestry for the fusion machinery of secretory. In summary, my group has contributed to the knowledge of unique parasite secretory organelles, their biogenesis, and exocytosis, and function of secreted proteins. This was possible through strategic collaborations with others.
Date: Monday, February 20, 2023
Time: 12-1 pm
Location: Hill 132 or Virtually Via Zoom
Questions? Please contact Michael Black if you have questions.