Investigating the relationship between two unique apicomplexan parasite organelles: the Eimeria refractile body and Plasmodium crystalloid

Apicomplexan parasites are widespread protozoan parasites of animals. The phylum Apicomplexa contains thousands of species and includes major pathogens of humans, domestic animals and livestock. For example, malaria (caused by Plasmodium spp.) causes nearly half a million human deaths per annum globally, while chicken coccidiosis (caused by Eimeria spp.) has an estimated global economic cost of >10 billion US$ per annum through losses in poultry production and treatment.

Plasmodium and Eimeria have evolved very different life cycles, nonetheless, their monophyletic ancestry has conserved many Apicomplexa-specific cellular structures and molecular processes involved in cell division, invasion, and motility, as well as two unique parasite structures: the 'crystalloid' of Plasmodium and the 'refractile body' (RB) of Eimeria. The crystalloid and RB share similar features such as their size and number: two crystalloids and RBs are found, which merge into a single organelle during transition into oocyst and schizont, respectively.

In recent years, studies in P. berghei have provided strong evidence for a spatial and functional link between the crystalloids and a family of LCCL domain-containing proteins (LAPs) that are essential for sporogony. The RBs are found exclusively in the sporozoite and young primary schizont life cycle stages of Eimeria and their roles in parasite development remain unresolved. Eimeria spp. encode several LAP orthologues and this project will test the hypothesis that Eimeria LAPs localise in the RB and are involved in the function of this organelle.