Abstract
BackgroundPlasmodium sporozoites are the highly motile forms of malaria-causing parasites that are transmitted by the mosquito to the vertebrate host. Sporozoites need to enter and cross several cellular and tissue barriers for which they employ a set of surface proteins. Three of these proteins are members of the thrombospondin related anonymous protein (TRAP) family. Here, potential additive, synergistic or antagonistic roles of these adhesion proteins were investigated.MethodsFour transgenic Plasmodium berghei parasite lines that lacked two or all three of the TRAP family adhesins TRAP, TLP and TREP were generated using positive–negative selection. The parasite lines were investigated for their capacity to attach to and move on glass, their ability to egress from oocysts and their capacity to enter mosquito salivary glands. One strain was in addition interrogated for its capacity to infect mice.ResultsThe major phenotype of the TRAP single gene deletion dominates additional gene deletion phenotypes. All parasite lines including the one lacking all three proteins were able to conduct some form of active, if unproductive movement.ConclusionsThe individual TRAP-family adhesins appear to play functionally distinct roles during motility and infection. Other proteins must contribute to substrate adhesion and gliding motility.Graphical
Highlights
Plasmodium sporozoites are the highly motile forms of malaria-causing parasites that are transmitted by the mosquito to the vertebrate host
Generation of Plasmodium berghei parasite lines lacking two and three thrombospondin related anonymous protein (TRAP) family adhesins In order to generate parasite lines lacking more than one TRAP family gene, a strategy based on sequential positive and negative selection [51] was employed (Fig. 1B)
Vectors for deletion of trep and tlp were engineered to replace the endogenous gene with the gene encoding for the red fluorescent protein mCherry controlled by the circumsporozoite protein promoter, which is strongly expressed throughout the life of sporozoites (Additional file 1: Fig. S1)
Summary
Plasmodium sporozoites are the highly motile forms of malaria-causing parasites that are transmitted by the mosquito to the vertebrate host. Sporozoites need to enter and cross several cellular and tissue barriers for which they employ a set of surface proteins. Sporozoites of avian parasites can already enter host cells and differentiate [22]. Sporozoites migrate through cells in the dermis, a capacity that is essential for entering the circulatory system [24, 25]. Sporozoites can enter both blood or lymph vessels [18] and those entering the blood are transported throughout the body to reach the liver [26, 27]. In the liver sporozoites enter and differentiate within hepatocytes into red cell infecting merozoites [25, 28, 29]
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