Mosquito Tissue Ultrastructure-Expansion Microscopy (MoTissU-ExM) enables ultrastructural and anatomical analysis of malaria parasites and their mosquito

Study of malaria parasite cell biology is challenged by their small size, which can make visualisation of individual organelles difficult or impossible using conventional light microscopy. In recent years, the field has attempted to overcome this challenge through the application of ultrastructure expansion microscopy (U-ExM), which physically expands a biological sample approximately 4.5-fold. To date, U-ExM has mostly been used to visualise blood-stage parasites and used exclusively on parasites in vitro.

Here we develop Mosquito Tissue U-ExM (MoTissU-ExM), a method for preparing dissected mosquito salivary glands and midguts by U-ExM. MoTissU-ExM preserves both host and parasite ultrastructure, enabling visualisation of oocysts and sporozoites in situ. We also provide a point-by-point protocol for how to perform MoTissU-ExM.

We validate that MoTissU-ExM samples expand as expected, provide a direct comparison of the same dissected tissues before and after MoTissU-ExM, and highlight some of the key host and parasite structures that can be visualised following MoTissU-ExM.

We discuss potential use cases for MoTissU-ExM for study of malaria parasite biology, and more broadly. We detail drawbacks or challenges MoTissU-ExM and imaging these expanded tissues, along with information troubleshooting this technique. Finally, we discuss how MoTissU-ExM could be applied and adapted in future to increase its utility.