Mutant/mutation
The mutant lacks expression of SERA4 and expresses GFP under the constitutive eef1a promoter

Protein (function)
The Plasmodium berghei PbSERA4 (PBANKA_0304800) gene encodes a cysteine-type SERA and is conserved and syntenic across the primate and rodent Plasmodium species. The predicted orthologue of PbSERA4 in Plasmodium falciparum is PfSERA7 (PF3D7_0207400), and the proteins encoded by these genes are 44% identical and 57% similar. Within the signature papain family cysteine protease domain (PFAM: PF00112), PbSERA4 and PfSERA7 share 66% amino acid identity and include the strictly conserved catalytic residues, i.e. an amino-terminal glutamine, the catalytic cysteine residue, a central histidine, and a carboxy-terminal asparagine.

Phenotype
Normal blood stage and mosquito stage development

Prolonged prepatent period (2 days) of blood stage infection after intravenous infection of mice with 10(5) sporozoites. 
Pbsera4(-) parasites reached levels equivalent to wildtype parasites in livers of infected animals 48 hours after infection. The parasite burden in livers infected by wildtype parasites drops by 72 hours after infection due to egress and merozoite release. Although the appearance of Pbsera4(-) parasites in the blood of sporozoite-infected animals is delayed, the Pbsera4(-) parasites do not appear to be retained in the liver at 72 hours after infection.
When Huh7 cells were infected, Pbsera4(-) sporozoites developed into exo-erythrocytic forms (EEF) in numbers similar to those formed by wildtype sporozoites. Pbsera4(-)-infected cultures generated approximately half the numbers of merosomes produced by wildtype-infected cultures. When equal numbers of wildtype or Pbsera4(-) merosomes produced by cultured cells were injected into mice, all mice developed a blood-stage infection, indicating that the Pbsera4(-) liver-stage merozoites that are generated are as capable of infecting red blood cells and establishing a blood-stage infection as wildtype merozoites.
Together, these data indicate that liver-stage Pbsera4(-) parasites are released inefficiently from infected cells, but that they are infectious to red blood cells.

Additional information
To examine protein expression and assess the localization of PbSERA4, we generated a transgenic P. berghei ANKA line that expresses fluorescently tagged PbSERA4 from the native PbSERA4 promoter (RMgm-4872). We detected PbSERA4-mCherry signal in late asexual blood stages and gametocytes, and we could observe red fluorescence throughout exflagellation of male gametes. We failed to detect a red fluorescent signal in PbSERA4-mCherry sporozoites isolated from mosquito midguts or salivary glands despite the presence of PbSERA4 transcripts. No mCherry signal could be detected in early liver-stage P. berghei. However fluorescent protein expression in both lines is evident later in the liver stage. PbSERA4-mCherry could be detected 48 hours after infection of cultured cells with PbSERA4-mCherry sporozoites. The PbSERA4-mCherry signal progressively increased, and late liver schizonts and liver merozoites exhibited bright fluorescence.

Other mutants