Mutant/mutation
A mutant with the endogenous csp gene replaced by a chimeric csp gene: the C-terminal region of P. galinaceum csp and the N-terminal and repeat regions of P. berghei csp.

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
Normal numbers of salivary gland sporozoites are produced and sporozoites show normal infectivity to mice. Mutants in which the complete P. berghei csp gene is replaced by the complete P gallinaceum csp gene show strongly reduced numbers of salivary gland sporozoites and sporozoites are not infective to mice. 
These observations suggest that the N-terminal region plays an important role in salivary gland infection. In addition, it indicates that  the N-terminal sequence is important for vertebrate infectivity.

Additional information
Staining of midgut sporozoites with anti-CSP antibodies showed normal expression, location. processing and release of the mutated CSP

Figure 1



Figure 1.
Schematic representation of the CS proteins present in each of the four transgenic P. berghei parasite lines generated.
PbCS^DHFR parasites carry the wildtype PbCS coding sequence (white boxes, RI and RII indicated with light and dark green respectively)
PgCS^SX parasites carry the full PgCS coding sequence (grey boxes, RI and RII indicated with light and dark blue respectively), but with the SpeI (S) and XhoI (X) restriction endonuclease sites inserted on either side of the repeat region.
PgCS/Pb^RR parasites contain the PgCS N-terminal and C-terminal regions (grey boxes) and the PbCS repeat region (white box).
PbCS/Pg^CT parasites carry the PbCS N-terminal and repeat regions (white boxes) and the PgCS C-terminal region (grey box).

Other mutants
RMgm-769: A mutant with endogenous P. berghei csp gene is replaced by the P. gallinaceum csp with introduced SpeI and XhoI sites flanking the repeat region.
RMgm-770: A mutant with the endogenous CSP replaced by a chimeric CSP: N- and C-terminal regions of P. galinaceum CSP and the repeat region of P. berghei CSP