Abstract
The SAS6-like (SAS6L) protein, a truncated paralogue of the ubiquitous basal body/centriole protein SAS6, has been characterised recently as a flagellum protein in trypanosomatids, but associated with the conoid in apicomplexan Toxoplasma. The conoid has been suggested to derive from flagella parts, but is thought to have been lost from some apicomplexans including the malaria-causing genus Plasmodium. Presence of SAS6L in Plasmodium, therefore, suggested a possible role in flagella assembly in male gametes, the only flagellated stage. Here, we have studied the expression and role of SAS6L throughout the Plasmodium life cycle using the rodent malaria model P. berghei. Contrary to a hypothesised role in flagella, SAS6L was absent during gamete flagellum formation. Instead, SAS6L was restricted to the apical complex in ookinetes and sporozoites, the extracellular invasive stages that develop within the mosquito vector. In these stages SAS6L forms an apical ring, as we show is also the case in Toxoplasma tachyzoites. The SAS6L ring was not apparent in blood-stage invasive merozoites, indicating that the apical complex is differentiated between the different invasive forms. Overall this study indicates that a conoid-associated apical complex protein and ring structure is persistent in Plasmodium in a stage-specific manner.
Highlights
The SAS6-like (SAS6L) protein, a truncated paralogue of the ubiquitous basal body/centriole protein SAS6, has been characterised recently as a flagellum protein in trypanosomatids, but associated with the conoid in apicomplexan Toxoplasma
To investigate the transcription of sas6l during the Plasmodium life cycle, we used qRT-PCR and showed sas6l RNA is transcribed throughout all parasite stages tested, with strongest expression seen in activated gametocytes (Fig. 1a)
The SAS6 paralogue, SAS6L, has been more intriguing with respect to its location and function in diverse eukaryotes[3]. While it is associated with the flagellum in trypanosomatids, it is associated with the conoid of the apical complex in T. gondii, adding weight to the hypothesis that this divergent structure in apicomplexans has some evolutionary link to flagellar structures[3,26]
Summary
The SAS6-like (SAS6L) protein, a truncated paralogue of the ubiquitous basal body/centriole protein SAS6, has been characterised recently as a flagellum protein in trypanosomatids, but associated with the conoid in apicomplexan Toxoplasma. SAS6L is widespread in eukaryotes absent from metazoans[3] This SAS6 paralogue lacks the coiled-coil domains that form the long radial spokes of the SAS6 complex, instead consisting primarily of the protein globular domain that, for SAS6, forms the oligomeric ring of nine dimers. It is not known what conformation or structures SAS6L is capable of forming, its location has been determined in both the trypanosomatid Trypanosoma brucei, that is permanently flagellate, and the apicomplexan Toxoplasma gondii. Not known: 1) what the functional contributions of these conoid-associated proteins are; 2) what other proteins contribute to conoid structure and function; and 3) how well conserved conoid composition and function is throughout Apicomplexa
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
