Authors

J Valli¹; E Johnson¹; E Gluenz¹;  ¹ University of Oxford, Sir William Dunn School of Pathology

Discussion

Parasites of the Leishmania mexicana complex reside within large, communal parasitophorous vacuoles (PVs), with parasites typically aligned along the PV membrane. Ultrastructural studies have reported close contact between amastigotes and the PV, either involving the posterior pole or flagellar tip, but how parasite positioning changes over time remains unexplored. We used 3D electron microscopy techniques to follow orientation of L. mexicana amastigotes within the PV at different time points after infection, and to explore the connectivity at contact sites. Models produced from serial block face scanning electron microscopy data suggest a progression in amastigote orientation over an infection time-course. Amastigote-PV contact was initially maintained at both the posterior end and flagellar tip, with the main vacuole volume bulging laterally away from the amastigote. Electron tomography showed infiltration of flagellar membrane tubules into invaginations of the PV membrane, and provided evidence of vesicular activity at the flagellar tip and PV membranes at contact sites. As PV size increased, flagellar contact was lost, leaving amastigotes with only their posterior ends embedded. PV enlargement has been shown to facilitate amastigote survival. Further work will be required to determine whether the membrane activity observed at regions of initial PV-flagellum contact could be involved in regulation of PV enlargement or modulation of other host cell functions.