Mutant/mutation
The mutant lacks expression of Actin II

Protein (function)
Actin, a cytoskeletal protein, has many diverse functions in eukaryotic cells ranging from roles in cell motility, cell division, vesicle trafficking to functions in cell signaling and regulation of transcription. A critical property of actin is its ability to form filamentous polymers (F-actin), and a plethora of proteins are involved in the highly dynamic regulation of F-actin formation . Actins are highly conserved proteins that often exist in multiple isoforms in the eukaryotic cell and their expression is regulated both spatially and temporally during development. The number of conventional actin genes varies among eukaryotic organisms. A few single cell eukaryotes, such as Saccharomyces cerevisiae, Toxoplasma gondii, and Trypanosoma brucei encode a single actin gene, which results in lethality when targeted with gene ablation approaches. Many organisms, however, have several conventional actin genes.Apicomplexan parasites all encode one major actin isoform, here termed Actin I. All apicomplexan parasites also contain a number of actin-related and actin-like proteins. Plasmodium species species stand out in that they all encode a second conventional actin, termed Actin II.

Phenotype
Phenotype analyses indicate that Actin II plays a major role during the formation of the male gametes (see also 'Additional information'). Female gametes are fertile as shown in cross-fertilisation studies with fertile male gametes.

Additional information
Evidence is presented that in activated male gametocytes of the mutant axonemes are formed but formation of active, beating flagella fails and male gametes appear to be defective in egress from the host erythrocyte.

Analyses of blood stages of a mutant expressing GFP under the control of the 1.2kb promoter region of actin II (RMgm-634) indicate 'upregulated expression the the male gametocytes' and low or absent actin II expression in asexual blood stages and female gametocytes.

Analyses of blood stages of a mutant expressing a GFP-tagged form of Actin II (RMgm-633) indicate  exclusive expression the the male gametocytes (male gamete).  Evidence is presented that the protein is located exclusively in the cytoplasm with no apparent accumulation to subcellular structures. Eight min after male activation the protein was observed in a narrow rim of cytoplasm surrounding the nucleus. In contrast Actin I was detected in both the cytoplasm and nuclei of non-activated gametocytes as shown by staining with an anti Actin I antibody. No specific localization of GFP-Actin II to the axonemes could be detected in double stainings of activated gametocytes/male gametes with an anti-tubulin antibody.
Evidence is presented that in activated males of wild type gametocytes Actin I relocalizes from the nucleus to the cytoplasm. This relocalisation was not observed in male gametes of the mutant lacking expression of Actin II.

The function of the mutant was restored by complementing the actII(-) line with the wild type actin II gene under control of it own promoter and regulated by the 3’UTR of the P. berghei dhfr-ts gene. The complementary actin II gene was inserted into the small subunit ribosomal rna gene (c-type unit) by single cross-over integration. In this complemented parasite line actIIC, actin II transcripts were readily detectable by RT-PCR. The complemented parasites were tested for exflagellation and ookinete conversion, which revealed partial complementation.

Other mutants
RMgm-633: A mutant expressing a GFP-tagged form of Actin II
RMgm-634: A mutant  expressing GFP under control of the promoter region of actin II