Basal body structure and composition in the apicomplexans Toxoplasma and Plasmodium

Maria E Francia,Naomi S Morrissette,Jean-Francois Dubremetz

doi:10.1186/s13630-016-0025-5

Abstract

The phylum Apicomplexa encompasses numerous important human and animal disease-causing parasites, including the Plasmodium species, and Toxoplasma gondii, causative agents of malaria and toxoplasmosis, respectively. Apicomplexans proliferate by asexual replication and can also undergo sexual recombination. Most life cycle stages of the parasite lack flagella; these structures only appear on male gametes. Although male gametes (microgametes) assemble a typical 9+2 axoneme, the structure of the templating basal body is poorly defined. Moreover, the relationship between asexual stage centrioles and microgamete basal bodies remains unclear. While asexual stages of Plasmodium lack defined centriole structures, the asexual stages of Toxoplasma and closely related coccidian apicomplexans contain centrioles that consist of nine singlet microtubules and a central tubule. There are relatively few ultra-structural images of Toxoplasma microgametes, which only develop in cat intestinal epithelium. Only a subset of these include sections through the basal body: to date, none have unambiguously captured organization of the basal body structure. Moreover, it is unclear whether this basal body is derived from pre-existing asexual stage centrioles or is synthesized de novo. Basal bodies in Plasmodium microgametes are thought to be synthesized de novo, and their assembly remains ill-defined. Apicomplexan genomes harbor genes encoding δ- and ε-tubulin homologs, potentially enabling these parasites to assemble a typical triplet basal body structure. Moreover, the UNIMOD components (SAS6, SAS4/CPAP, and BLD10/CEP135) are conserved in these organisms. However, other widely conserved basal body and flagellar biogenesis elements are missing from apicomplexan genomes. These differences may indicate variations in flagellar biogenesis pathways and in basal body arrangement within the phylum. As apicomplexan basal bodies are distinct from their metazoan counterparts, it may be possible to selectively target parasite structures in order to inhibit microgamete motility which drives generation of genetic diversity in Toxoplasma and transmission for Plasmodium.

Highlights

The phylum Apicomplexa encompasses numerous important human and animal disease-causing parasites, includ‐ ing the Plasmodium species, and Toxoplasma gondii, causative agents of malaria and toxoplasmosis, respectively
The phylum Apicomplexa encompasses numerous important disease-causing pathogens including the agents of malaria, toxoplasmosis, cryptosporidiosis, Texas and East Coast fever, and coccidiosis
Apicomplexa use distinct cell division schemes of fascinating complexity and variability to adapt to different hosts and suit specific intracellular niches [7]

Summary

Introduction

The phylum Apicomplexa encompasses numerous important human and animal disease-causing parasites, includ‐ ing the Plasmodium species, and Toxoplasma gondii, causative agents of malaria and toxoplasmosis, respectively. The invasive asexual stages of apicomplexans are not flagellated, and neither of these MTOCs functions as a basal body. In both Toxoplasma and Plasmodium, only the male gamete, known as the microgamete, assembles basal bodies and flagella (Fig. 1d, e).

Results

Conclusion