Additional remarks phenotype | Mutant/mutation
The mutant lacks expression of SAS4 and expresses GFP under the constitutive ef1a promoter
Protein (function)
Centriole/basal bodies (CBBs) are associated with the microtubule organising centre (MTOC) that nucleates cilia, flagella, and centrosomes and are conserved ancestral organelles in eukaryotes. Centrioles and basal bodies (BBs) share structural features and BBs are mainly associated with flagella or cilia organisation, and extend to produce an axoneme. The canonical view of CBB biogenesis includes centriole duplication and segregation to a daughter cell during mitosis. However, in some organisms, BB biology is more diverse, for example, where the centrioles or BBs form de novo or exhibit non- canonical biogenesis, as observed in Naegleria and in some parthenogenic insect eggs.SAS4/SAS6 are ancestral core proteins involved in BB biogenesis, as predicted by phylogenetic analysis. Clear centrioles with 9 + 1 or 9 + 2 microtubules can only be seen in flagella biogenesis during male gamete formation in Plasmodium.
The centriole/basal body (CBB) is an evolutionarily conserved organelle acting as a microtubule organising centre (MTOC) to nucleate cilia, flagella, and the centrosome. SAS4/CPAP is a conserved component associated with BB biogenesis in many model flagellated cells. Plasmodium, a divergent unicellular eukaryote and causative agent of malaria, displays an atypical, closed mitosis with an MTOC (or centriolar plaque), reminiscent of an acentriolar MTOC, embedded in the nuclear membrane. Mitosis during male gamete formation is accompanied by flagella formation. There are two MTOCs in male gametocytes: the acentriolar nuclear envelope MTOC for the mitotic spindle and an outer centriolar MTOC (the basal body) that organises flagella assembly in the cytoplasm.
Phenotype
No significant difference in male gamete formation in the Δsas4 parasite in comparison with the WT-GFP parasite. Electron micrographs of gametocytes activated for 4–5 min (early) showed no difference between Δsas4 and WT-GFP parasites. Similarly, there were no differences in electron micrographs of exflagellating gametocytes activated for 15 min (late). Zygote formation, ookinete, oocyst and sporozoite production and infectivity comparable to WT-GFP parasites.
Additional information
From the Abstract:
'We show the coordinated location, association and assembly of SAS4 with the BB component, kinesin- 8B, but no association with the kinetochore protein, NDC80, indicating that SAS4 is part of the BB and outer centriolar MTOC in the cytoplasm. Deletion of the SAS4 gene produced no phenotype, indicating that it is not essential for either male gamete formation or parasite transmission'.
See also mutant RMgm-5153 for another mutant lacking expression of SAS4 that showed a different phenotype (Deletion of sas4 led to a 90% decrease in the formation of active exflagellation centres).
Other mutants |