Disruption of Plasmodium berghei merozoite surface protein 7 gene modulates parasite growth in vivo.

Merozoite invasion of red blood cells is crucial to the development of the parasite that causes malaria. Merozoite surface proteins (MSPs) mediate the first interaction between parasite and erythrocyte. In Plasmodium falciparum, they include a complex of products from at least 3 genes (msp1, msp6, and msp7), one of which, msp7, is part of a gene family containing 3 and 6 adjacent members in Plasmodium yoelii and Plasmodium falciparum, respectively. We have identified and disrupted msp7 in the Plasmodium berghei gene family. The protein is expressed in schizonts and colocalizes with MSP1. The synthesis and processing of MSP1 was unaffected in the parasite with the disrupted gene (MSP7ko). Disruption of msp7 was not lethal but affected blood-stage parasite growth. MSP7ko parasites initially grew more slowly than wild-type parasites. However, when reticulocytes were prevalent, the rate of increase in parasitemia was similar, suggesting that MSP7ko parasites prefer to invade and grow within reticulocytes.