Honors & Awards

  • ChEM-H Postdoc at the Interface Seed Grant, Stanford University (2020)
  • Maternal and Child Health Research Institute Postdoctoral Support, Stanford University (2019)
  • School of Medicine Dean’s Postdoctoral Fellowship, Stanford University (2018)
  • Vaadia-BARD Postdoctoral Fellowship, Vaadia-BARD (2018)

Education & Certifications

  • Master of Science, The Weizmann Institute of Science (2012)
  • Doctor of Philosophy, The Weizmann Institute of Science (2017)

All Publications

  • Cryo-electron tomography with mixed-scale dense neural networks reveals key steps in deployment of Toxoplasma invasion machinery. PNAS nexus Segev-Zarko, L. A., Dahlberg, P. D., Sun, S. Y., Pelt, D. M., Kim, C. Y., Egan, E. S., Sethian, J. A., Chiu, W., Boothroyd, J. C. 2022; 1 (4): pgac183


    Host cell invasion by intracellular, eukaryotic parasites within the phylum Apicomplexa is a remarkable and active process involving the coordinated action of apical organelles and other structures. To date, capturing how these structures interact during invasion has been difficult to observe in detail. Here, we used cryogenic electron tomography to image the apical complex of Toxoplasma gondii tachyzoites under conditions that mimic resting parasites and those primed to invade through stimulation with calcium ionophore. Through the application of mixed-scale dense networks for image processing, we developed a highly efficient pipeline for annotation of tomograms, enabling us to identify and extract densities of relevant subcellular organelles and accurately analyze features in 3-D. The results reveal a dramatic change in the shape of the anteriorly located apical vesicle upon its apparent fusion with a rhoptry that occurs only in the stimulated parasites. We also present information indicating that this vesicle originates from the vesicles that parallel the intraconoidal microtubules and that the latter two structures are linked by a novel tether. We show that a rosette structure previously proposed to be involved in rhoptry secretion is associated with apical vesicles beyond just the most anterior one. This result, suggesting multiple vesicles are primed to enable rhoptry secretion, may shed light on the mechanisms Toxoplasma employs to enable repeated invasion attempts. Using the same approach, we examine Plasmodium falciparum merozoites and show that they too possess an apical vesicle just beneath a rosette, demonstrating evolutionary conservation of this overall subcellular organization.

    View details for DOI 10.1093/pnasnexus/pgac183

    View details for PubMedID 36329726

    View details for PubMedCentralID PMC9615128

  • Cryo-ET of Toxoplasma parasites gives subnanometer insight into tubulin-based structures. Proceedings of the National Academy of Sciences of the United States of America Sun, S. Y., Segev-Zarko, L., Chen, M., Pintilie, G. D., Schmid, M. F., Ludtke, S. J., Boothroyd, J. C., Chiu, W. 2022; 119 (6)


    Tubulin is a conserved protein that polymerizes into different forms of filamentous structures in Toxoplasma gondii, an obligate intracellular parasite in the phylum Apicomplexa. Two key tubulin-containing cytoskeletal components are subpellicular microtubules (SPMTs) and conoid fibrils (CFs). The SPMTs help maintain shape and gliding motility, while the CFs are implicated in invasion. Here, we use cryogenic electron tomography to determine the molecular structures of the SPMTs and CFs in vitrified intact and detergent-extracted parasites. Subvolume densities from detergent-extracted parasites yielded averaged density maps at subnanometer resolutions, and these were related back to their architecture in situ. An intralumenal spiral lines the interior of the 13-protofilament SPMTs, revealing a preferred orientation of these microtubules relative to the parasite's long axis. Each CF is composed of nine tubulin protofilaments that display a comma-shaped cross-section, plus additional associated components. Conoid protrusion, a crucial step in invasion, is associated with an altered pitch of each CF. The use of basic building blocks of protofilaments and different accessory proteins in one organism illustrates the versatility of tubulin to form two distinct types of assemblies, SPMTs and CFs.

    View details for DOI 10.1073/pnas.2111661119

    View details for PubMedID 35121661

  • Cryogenic electron tomography reveals novel structures in the apical complex of Plasmodium falciparum. mBio Sun, S. Y., Segev-Zarko, L., Pintilie, G. D., Kim, C. Y., Staggers, S. R., Schmid, M. F., Egan, E. S., Chiu, W., Boothroyd, J. C. 2024: e0286423


    Intracellular infectious agents, like the malaria parasite, Plasmodium falciparum, face the daunting challenge of how to invade a host cell. This problem may be even harder when the host cell in question is the enucleated red blood cell, which lacks the host machinery co-opted by many pathogens for internalization. Evolution has provided P. falciparum and related single-celled parasites within the phylum Apicomplexa with a collection of organelles at their apical end that mediate invasion. This apical complex includes at least two sets of secretory organelles, micronemes and rhoptries, and several structural features like apical rings and a putative pore through which proteins may be introduced into the host cell during invasion. We perform cryogenic electron tomography (cryo-ET) equipped with Volta Phase Plate on isolated and vitrified merozoites to visualize the apical machinery. Through tomographic reconstruction of cellular compartments, we see new details of known structures like the rhoptry tip interacting directly with a rosette resembling the recently described rhoptry secretory apparatus (RSA), or with an apical vesicle docked beneath the RSA. Subtomogram averaging reveals that the apical rings have a fixed number of repeating units, each of which is similar in overall size and shape to the units in the apical rings of tachyzoites of Toxoplasma gondii. Comparison of these polar rings in Plasmodium and Toxoplasma parasites also reveals them to have a structurally conserved assembly pattern. These results provide new insight into the essential and structurally conserved features of this remarkable machinery used by apicomplexan parasites to invade their respective host cells.Malaria is an infectious disease caused by parasites of the genus Plasmodium and is a leading cause of morbidity and mortality globally. Upon infection, Plasmodium parasites invade and replicate in red blood cells, where they are largely protected from the immune system. To enter host cells, the parasites employ a specialized apparatus at their anterior end. In this study, advanced imaging techniques like cryogenic electron tomography (cryo-ET) and Volta Phase Plate enable unprecedented visualization of whole Plasmodium falciparum merozoites, revealing previously unknown structural details of their invasion machinery. Key findings include new insights into the structural conservation of apical rings shared between Plasmodium and its apicomplexan cousin, Toxoplasma. These discoveries shed light on the essential and conserved elements of the invasion machinery used by these pathogens. Moreover, the research provides a foundation for understanding the molecular mechanisms underlying parasite-host interactions, potentially informing strategies for combating diseases caused by apicomplexan parasites.

    View details for DOI 10.1128/mbio.02864-23

    View details for PubMedID 38456679

  • Actin self-organization in gliding parasitic cells Hueschen, C. L., Zarko, L., Chen, J., LeGros, M., Larabell, C. A., Boothroyd, J. C., Phillips, R., Dunn, A. R. CELL PRESS. 2023: 5A
  • Actin self-organization in gliding parasitic cells. Biophysical journal Hueschen, C. L., Segev Zarko, L., Chen, J., LeGros, M., Larabell, C. A., Boothroyd, J. C., Phillips, R., Dunn, A. R. 2023; 122 (3S1): 5a

    View details for DOI 10.1016/j.bpj.2022.11.263

    View details for PubMedID 36784911

  • Characterizing the distribution of myosin H in the apical complex of conoid protruded and conoid retracted Toxoplasma gondii Balaji, A., Dahlberg, P. D., Segev-Zarko, L., Sun, S., Chiu, W., Boothroyd, J., Moerner, W. E. CELL PRESS. 2022: 409A
  • NANOSCALE ELUCIDATION OF THE INVASION APPARATUS OF APICOMPLEXAN PARASITES Segev-Zarko, L., Sun, S. Y., Dahlberg, P. D., Pelt, D., Chen, J., Schmid, M. F., Galaz-Montoya, J., Moerner, W. E., Larabell, C., Sethian, J., Chiu, W., Boothroyd, J. AMER SOC TROP MED & HYGIENE. 2019: 620