Mutant/mutation
The mutant expresses a truncated form of merozoite surface protein 8 (MSP8). The truncated gene lacks the C-terminal EGF domains and the GPP-anchor sequence.

Protein (function)
MSP8 is a glycosylphosphatidyl inositol (GPI)-anchored membrane protein. A distinctive feature of this protein is a C-terminal double epidermal growth factor (EGF)-like domain resembling that seen in the dominantly expressed merozoite surface protein, MSP1.
The exact location of the protein is not clear but evidence has been presented for a localisation in the parasitophorous vacuole membrane in the ring stage and in the food vacuole in older trophozoites.

Phenotype
The phenotype analyses indicate that the lack of expression of MSP8 does not affect in vivo blood-stage development.

Additional information
Wild-type P. berghei has a preference for invading reticulocytes, however, at low parasite burdens in mice the majority of parasites can be found inside mature erythrocytes (normocytes), which is reflective of the high normocyte:reticulocyte ratio during the early stages of infection. As the levels of parasitemia increase, there is a marked increase in circulating reticulocytes in response to the decrease in erythrocyte levels, such that reticulocytes account for up to 40% of circulating cells. With its preference for reticulocytes, therefore, the overwhelming majority of parasites can be found inside reticulocytes in the latter stages of infection. A similar finding to the wild-type parent was observed with the ΔMSP8 parasite line, in that there was no difference in the overall growth rates in Balb/c mice, nor was there a significant difference in overall reticulocyte preference at any time point, also not when only normocytes were observed

MSP8 expression has been analysed by Western analysis and IFA. A time course analysis of MSP8 expression in blood stages showed predominant expression in the trophozoite stage, substantially earlier than schizont-specific antigens such as MSP1. MSP8 was also detected in the ring-stages and by immunofluorescence assay (IFA) it was found to localise to the parasitophorous vacuole. By schizont stages, however, MSP8 was present in the food vacuole. For merozoites weak apical reactivity was observed with the anti-MSP8 antibodies in IFA but was indistinguishable in the mutant and wild-type parasites. 

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