Mutant/mutation
The mutant lacks expression of MTRAP and expresses nanoluciferase under control of the (ookinete specific) ctrp promoter. The nanoluciferase expression cassette has been integrated into the neutral 230p locus.

Protein (function)
The thrombospondin-related anonymous protein (TRAP) family of proteins are type I transmembrane proteins that share a functionally conserved cytoplasmic tail and an ectodomain exposing various ligand-binding modules including a thrombospondin type I repeat (TSR). In Plasmodium, the sporozoite stage expresses three members of the family—TRAP; TRAP-related protein (TREP), also called S6; and TRAP-ike protein (TLP)—which all play a role in sporozoite gliding on substrates and within tissues. The ookinete stage expresses a single member, called circumsporozoite protein and thrombospondin-related anonymous protein-related protein (CTRP), which is essential for ookinete gliding motility.
Merozoite TRAP (MTRAP) is a TRAP family member that was reported as expressed in the merozoite. The mtrap gene is conserved and syntenic among Plasmodium species.

Analyses of P. berghei mutants lacking expression of MTRAP (RMgm-1493, RMgm-4056) showed a role of MTRAP in rupture of the parasitophorous membrane of gametocytes, resulting in escape of gametes resulting in absence of fertilisation and ookinete formation.

Phenotype
To verify if the increase in nanoluciferase (nLuc) activity in (ookinete) conversion assays with Ookluc (RMgm-4518) was  dependent on fertilization, we deleted the mtrap gene from the Ookluc genome. MTRAP-knockout (MTRAP-KO) gametocytes can activate, but the gametes remain trapped inside the host cell. There was no increase of nLuc activity in Ookluc-MTRAP-KO parasites after 24 hr of conversion assay – the absence of ookinetes was confirmed by blood smears – showing that gametocyte activation per se is not sufficient for activation of the ctrp promoter, hence nLuc expression and activity in Ookluc parasites depend on gamete egress and fertilization.

Additional information
From the Abstract:
'Here we demonstrate the generation of a Plasmodium model for drug screens against  gametes and fertilization. The new P. berghei line, named Ookluc, was genetically and pharmacologically validated and scalable for HTS. Screening the Pathogen Box from the Medicines for Malaria Venture (MMV) using the new model identified promising TB compounds. The use of Ookluc in different libraries of compounds may aid in the identification of transmission-blocking drugs not assessed in screens against asexual stages or gametocytes.'

Other mutants
P. berghei mutants lacking expression of MTRAP (RMgm-1493, RMgm-4056)