Mutant/mutation
The mutant lacks expression of PbSR-MG (similar mutants were made in the following background parent lines: a reporter P. berghei ANKA line expressing mCherry in female gametocytes and GFP in male gametocytes (RMgm-164) and in a reporter line expressing tdTomato in all blood stages (RMgm-4178).

Protein (function)
Serine-arginine–rich (SR) proteins are major regulators of alternative splicing, with regular expression levels necessary for maintaining normal alternative splicing and viability. One SR protein, PBANKA_0921600, is specifically upregulated in male gametocytes of P. berghei and downregulated in female gametocytes, and phylogenetic analysis identifies this gene as an orthologue of a known splicing factor in T. gondii. We named PBANKA_0921600 PbSR-MG (P. berghei SR protein male gametocytes).

Localizing an integrated, hemagglutinin-tagged (HA-tagged) PbSR-MG confirmed its expected nuclear localization (see mutant RMgm-4658)

Phenotype
Normal gametocyte production. Activation of female gametocytes normal. Male exflagellation, however, strongly reduced. Flagella stained with an anti-tubulin antibody remain curled within the gametocyte body. Motility of male free gametes strongly impaired.
Ablation of PbSR-MG also resulted in fewer oocysts per mosquito host. To test if this difference solely reflected the defect in exflagellation, we repeated the mosquito infection using equal numbers of in vitro generated ookinetes. Despite exposing mosquitoes to equal infective load, we still observed a significant difference in oocyst numbers in PbSR-MG KO compared to wild-type parental parasites.

Additional information
Localizing an integrated, hemagglutinin-tagged (HA-tagged) PbSR-MG confirmed its expected nuclear localization (see mutant RMgm-4658).

Evidence is presented for the following: 
- RNA-seq analysis revealed differences in alternative splicing to be heavily skewed by sex in the mutant lacking PbSR-MG. Ten percent of genes had modified alternative splicing in male gametocytes, while only 3.9% of female-specific and 0.90% of asexual-stage genes were affected. Loss of PbSR-MG had minimal impact on transcription, altering the overall expression of only 0.5% of genes. 
- There were 247 genes that had both male-specific changes in alternative splicing and were male genes regulated by PbSR-MG. Hence, 79% (247/314) of the genes regulated by PbSR-MG were originally identified as having alternative splicing changes specific tomale gametocytes. Fromthe opposing perspective, only 20% (247/1238) of all male-specific alternative splicing changes are regulated by PbSR-MG. This contrasts with female gametocytes, where only 5.4% (73/1340) of the female-specific alternative splicing changes are affected by the deletion of PbSR-MG. Presumably, there are other unidentified factors regulating female-specific alternative splicing. 
- When PbSRMGwas ablated, the number of alternatively spliced genes detected was relatively unchanged for asexual parasites  modestly increased for female gametocytes, and most increased for male gametocytes. Many genes were alternatively spliced in both wild-type and mutant parasites, suggesting that much alternative splicing is regulated by factors additional to PbSR-MG in all three stages. 

Other mutants