Identification of Tissue Cyst Wall Components by Transcriptome Analysis of In Vivo and In Vitro Toxoplasma gondii Bradyzoites

The Toxoplasma gondii bradyzoite is essential to establish persistent infection, yet little is known about what factors this developmental form secretes to establish the cyst or interact with its host cell. To identify candidate bradyzoite-secreted effectors, the transcriptomes of in vitro tachyzoites 2 days postinfection, in vitro bradyzoites 4 days postinfection, and in vivo bradyzoites 21 days postinfection were interrogated by microarray, and the program SignalP was used to identify signal peptides indicating secretion. One hundred two putative bradyzoite-secreted effectors were identified by this approach. Two candidates, bradyzoite pseudokinase 1 and microneme adhesive repeat domain-containing protein 4, were chosen for further investigation and confirmed to be induced and secreted by bradyzoites in vitro and in vivo. Thus, we report the first analysis of the transcriptomes of in vitro and in vivo bradyzoites and identify two new protein components of the Toxoplasma tissue cyst wall.