Transcriptome of axenic liver stages of Plasmodium yoelii.

Plasmodium liver stages or early exo-eythrocytic forms (EEFs) contain antigens that are essential for achieving sterile, protective immunity against malaria. Yet, attempts at identifying these antigens have been hampered by the challenge of obtaining large numbers of purified EEFs, uncontaminated with hepatocyte material. Using a recently described system for producing axenically cultured EEFs from Plasmodium yoelii, we have constructed a cDNA library and generated 1453 expressed sequence tags (ESTs) resulting in 652 unique transcripts. Analysis of the library provides insight into processes required for the initiation and development of Plasmodium liver stages, such as protein degradation, cell cycle progression and nutrient transport. Analysis of the gene expression profile of liver stages, as revealed by this library, suggests that liver stages represent a shift from "sporozoite-like" to "blood-stage-like". This is the first study of the transcriptional repertoire of Plasmodium liver stages.