Mutant/mutation
The mutant expresses a C-terminal GFP-tagged version of SAS6L

Protein (function)
The spindle assembly abnormal 6 homolog (SAS6) protein is required for early centriole assembly and coordinated basal body formation in a multitude of eukaryotes including humans. Flagella initiate from this centriole/ basal body and typically consist of a 9+2 formation of microtubules. SAS6 is ubiquitous in flagellated eukaryotes including apicomplexan parasites. See also the P. berghei mutant RMgm-1109 that lacks expression of SAS6. Gene deletion shows that SAS6 has a role in the formation of viable and motile flagella in P. berghei male gametes.

Recently a paralogue of SAS6, SAS6-like (SAS6L), has been investigated in two disparate eukaryotes, Toxoplasma and Trypanosoma. SAS6L is widespread in eukaryotes although absent from metazoans. in T. gondii, SAS6L is not located near SAS6 at the centriole, but instead at the apical end of the cell, specifically at the distal region of the conoid within the apical complex. The conoid is a conspicuous feature of many apicomplexans and is found at the centre of the apical complex—the defining feature of Apicomplexa and major instrument for host cell invasion.
The conoid is a collar-shaped structure that sits within the apical polar ring, although separate from it, just beneath the apical portion of the plasma membrane. In taxa such as T. gondii it is highly mobile, retracted posterior to the apical polar ring when growing within host cells, but dynamically relocated through and anterior to the apical polar ring during invasion events. Plasmodium has been traditionally considered to lack the conoid (it is classified in the Aconoidasida) based on ultrastructural data, particularly for the blood-stage merozoite. In this paper evidence is presented that SAS6L is not associated with the basal body of microgamete flagella, but instead, like in Toxoplasma, is associated with the apical complex where it forms a ring. Furthermore, this ring is absent in merozoites found in the mammalian host (liver and blood), but present in both ookinetes and sporozoites during the stages that form within the mosquito vector. These data suggest that there are distinct compositions of the apical complex that occur between the different zoite stages of Plasmodium, and that conoid-associated proteins are present in Plasmodium despite the apparent loss of the tubulin component of this structure.

Phenotype
Phenotype analyses of a mutant lacking expression of SAS6L (RMgm-1477) showed the following: Normal progression throughout the complete life cycle (in vertebrate and mosquito host, blood stages and liver stages).

Phenotype analyses of the mutant expressing GFP-tagged SAS6L showed the following: No expression in blood stages, merozoites and male gametocyets/gametes. A strong cytosolic localisation was seen in female gametocytes/gametes. After fertilization, this cytosolic staining was retained in zygotes along with the appearance of a dot at the periphery of the zygote. The cytosolic staining was progressively lost during later stages of ookinete development however this dot remains localised to the ookinete apical end. During sporozoite formation in oocysts at 14 days post-infection (dpi), the SAS6L-GFP signal is, again, faintly cytosolic, with small GFP dots observable corresponding to the ends of individual sporozoites. Isolated individual salivary gland sporozoites confirmed these dots to be present at the cell extremity.

Additional information
In this paper evidence is presented that SAS6L is not associated with the basal body of microgamete flagella, but instead, like in Toxoplasma, is associated with the apical complex where it forms a ring. Furthermore, this ring is absent in merozoites found in the mammalian host (liver and blood), but present in both ookinetes and sporozoites during the stages that form within the mosquito vector. These data suggest that there are distinct compositions of the apical complex that occur between the different zoite stages of Plasmodium, and that conoid-associated proteins are present in Plasmodium despite the apparent loss of the tubulin component of this structure.

Other mutants
RMgm-1477: A mutant lacking expression of SAS6L