Mutant/mutation
The mutant expresses the ookinete surface protein P25 of P. falciparum (Pfs25). Pfs25 is under the control of the 5'-UTR and 3'-UTR regulatory regions p25 of P. berghei. The pfs25 gene is introduced in the p25-p28 locus of P. berghei, thereby disrupting both p25 and p28 which encode two major ookinete surface proteins of P. berghei.

Protein (function)
P25 is one of two major surface proteins (P25 and P28) of the plasma membrane of ookinetes. The proteins are conserved between different Plasmodium species. The proteins are characterized by a secretory N-terminal signal sequence followed by three or four epidermal growth factor (EGF) domains and a glycosylphosphatidylinositol (GPI) anchor. Synthesis of both proteins begins between 0.5 and 2 h after the formation of the female gametes, and the proteins are still present in young oocysts. The paralogous genes encoding P25 and P28 are located next to each other in the genome in a head to tail organization. Antibodies against P25 prevent the formation of oocysts in the mosquito and thereby block transmission of the parasite.

Phenotype
The phentype analyses of oocyst production indicate  that Pfs25 was able to functionally complement the combined functions of Pb25 and Pb28 without compromising parasite growth and infectivity to A. stephensi mosquitoes (see also RMgm-1, RMgm-2 and RMgm-3 for the phenotype of P. berghei mutants lacking expression of either P25 and P28 alone or lacking both proteins). Analysis of expression by IFA shows expression of Pfs25 in the  ookinete stage. The protein is located on the surface of ookinetes.

Additional information
Experiments described in the paper show that immune sera from nonhuman primates immunized with a Pfs25-based vaccine when passively transferred to mice blocked transmission of TrPfs25Pb to Anopheles stephensi mosquitoes Furthermore, mice immunized with Pfs25 DNA vaccine and challenged with TrPfs25Pb displayed reduced malaria transmission compared to mice immunized with wild-type plasmid. These results show that the P. berghei mutant TrPfs25Pb can be used as a model for assessment of P. falciparum transmission-blocking vaccine.

Other mutants
RMgm-222, RMgm-223: P. berghei transgenic mutants expressing P25 of P. vivax.