Mutant/mutation
In the mutant the endogenous P. berghei CS is replaced by P. falciparum CS (circumsporozoite protein). The construct used to generate the mutant is the same construct used for mutant RMgm-69.

Protein (function)
The CS protein is the major protein on the surface of sporozoites and is critical for development of sporozoites within the oocysts and is involved in motility and invasion of both the salivary gland of the mosquito and the liver cells. The protein is also found on the oocyst plasma membrane and on the inner surface of the oocyst capsule. Specific motifs in CS are involved in sporozoite binding to mosquito salivary glands and in sporozoite attachment to heparan sulfate proteoglycans in the liver of the mammalian host. During substrate-dependent locomotion of sporozoites, CS is secreted at the sporozoite anterior pole, translocated along the sporozoite axis and released on the substrate at the sporozoite posterior pole. Following sporozoite invasion of hepatocytes, the CS is released in the host cell cytoplasm.

Phenotype
The phenotype analyses show that the CS protein of P. falciparum can (partly) complement the activity of the endogenous P. berghei CS protein.

Normal numbers of oocysts and oocyst-derived sporozoites are formed. However, mutant sporozoites invade less well the salivary glands (data from G.J. van Gemert,  RUNMC, Nijmegen, The Netherlands). Moreover, the mutant sporozoites appear to be less infective to the mammalian host. In a small number of experiments a lower infectivity was observed as determined  by RT-PCR, in vivo imaging of liver stages (luciferase/luminescence measurement; Ploemen et al., 2009, PloS One 18;4(11):e7881) and measurement of the prepatent period (unpublished observations C.J. Janse, LUMC, Leiden, The Netherlands and H. Kuipers, Crucell, Leiden, The Netherlands).

See also mutant RMgm-69 for an independent mutant in which the endogenous P. berghei CS is replaced by P. falciparum CS using the same construct. Sporozoites of this mutant also showed a reduced invasion rate of the salivary glands; however, it has been reported that the sporozoite infectivity was similar to that of wild type sporozoites as determined by the prepatent period after intravenous injection of sporozoites.

Additional information

Other mutants
A P. berghei ANKA 2.34 mutant has been generated in which the endogenous P. berghei CS is replaced by P. falciparum CS (RMgm-69)
A P. berghei mutant has been generated in which the endogenous P. berghei CS was replaced with P. gallinaceum CS (RMgm-74).
A P. berghei mutant has been generated in which the endogenous P. berghei CS was replaced with P. yoelii CS (RMgm-75).