Abstract
BackgroundPlasmodium falciparum sexual development plays a fundamental role in the transmission and spread of malaria. The ability to generate gametocytes can be lost during culture in vitro, often associated with the loss of a subtelomeric region of chromosome 9. Gametocytogenesis starts with erythrocyte invasion by a sexually committed merozoite, but the first available specific marker of sexual differentiation appears only from 24 h post invasion.MethodsSpecific antibodies and gene fusions were produced to study the timing of expression and the sub-cellular localization of the P. falciparum Gametocyte EXported Protein-5 (PfGEXP5), encoded in the subtelomeric region of chromosome 9. Expression patterns were examined in wild-type parasites and in parasite lines mutated in the Apetala2-G (AP2-G) transcription factor, governing a cascade of early sexual stage specific genes.ResultsPfGEXP5 is highly expressed in early sexual stages and it is actively exported to the infected erythrocyte cytoplasm from as early as 14 h post-invasion in haemozoin-free, ring stage-like parasites. The pattern of PfGEXP5 expression and export is similar in wild-type parasites and in independent AP2-G defective parasite lines unable to produce gametocytes.ConclusionsPfGEXP5 represents the earliest post-invasion sexual stage marker described to date. This provides a tool that can be used to identify sexually committed ring stage parasites in natural infections. This early gametocyte marker would enable the identification and mapping of malaria transmission reservoirs in human populations and the study of gametocyte sequestration dynamics in infected individuals. The fact that regulation of PfGEXP5 does not depend on the AP2-G master regulator of parasite sexual development suggests that, after sexual commitment, differentiation progresses through multiple checkpoints in the early phase of gametocytogenesis.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-015-0853-6) contains supplementary material, which is available to authorized users.
Highlights
Plasmodium falciparum sexual development plays a fundamental role in the transmission and spread of malaria
P. falciparum Gametocyte EXported Protein-5 (PfGEXP5) is expressed in early stage gametocytes and exported to the host cell cytoplasm The two-exon gene pfgexp5 (PF3D7_0936600) encodes a protein with a predicted molecular mass of 34,909 Da
The mouse antiserum was used to probe a Western blot of a sample of stage III gametocytes that had been treated with Equinatoxin-II (EqtII) [38] to selectively permeabilize the red blood cell (RBC) membrane (Fig. 1a)
Summary
Plasmodium falciparum sexual development plays a fundamental role in the transmission and spread of malaria. Malaria is a vector-borne disease caused by the genus Plasmodium. Parasite sexual commitment occurs in the asexual generation preceding gametocytogenesis, where each individual schizont produces a progeny of merozoites that uniformly develop into either asexual parasites or sexual parasites of the same sex [5,6,7]. It is currently debated whether in natural infections a constant fraction of parasites converts to sexual development during each asexual cycle or whether commitment is an environment-sensitive, triggered event [8]
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