Regulation of XXXX Oocyst Development by Strain- and Stage-Specific Small-Subunit rRNA.

@entity19 @entity311 @entity245 @entity501
One unique feature of @entity311 parasites is the differential transcription of structurally distinct rRNA (rRNA) genes at different developmental stages: the A-type genes are transcribed mainly in asexual stages, whereas the S-type genes are expressed mostly in sexual or mosquito stages. Conclusive functional evidence of different rRNAs in regulating stage-specific parasite development, however, is still absent. Here we performed genetic crosses of @entity501 parasites with one parent having an @entity245 ( @entity245 ) phenotype and another producing normal oocysts to identify the gene(s) contributing to the @entity245 . The parent with @entity245 -characterized as having small oocysts and lacking infective sporozoites-was obtained after introduction of a plasmid with a green fluorescent protein gene into the parasite genome and subsequent passages in @entity19 . Quantitative trait locus analysis of genome-wide microsatellite genotypes of 48 progeny from the crosses linked an ~200-kb segment on chromosome 6 containing one of the S-type genes (D-type small subunit rRNA gene [D-ssu]) to the @entity245 . Fine mapping of the plasmid integration site, gene expression pattern, and gene knockout experiments demonstrated that disruption of the D-ssu gene caused the @entity245 phenotype. Interestingly, introduction of the D-ssu gene into the same parasite strain (self), but not into a different subspecies, significantly affected or completely ablated oocyst development, suggesting a stage- and subspecies (strain)-specific regulation of oocyst development by D-ssu. This study demonstrates that @entity501 D-ssu is essential for normal oocyst and sporozoite development and that variation in the D-ssu sequence can have dramatic effects on parasite development. IMPORTANCE: @entity311 parasites are the only known organisms that express structurally distinct rRNA genes at different developmental stages. The differential expression of these genes suggests that they play unique roles during the complex life cycle of the parasites. Conclusive functional proof of different rRNAs in regulating parasite development, however, is still absent or controversial. Here we functionally demonstrate for the first time that a stage-specifically expressed D-type small-subunit rRNA gene (D-ssu) is essential for oocyst development of the @entity311 parasite @entity501 in the mosquito. This study also shows that variations in D-ssu sequence and/or the timing of transcription may have profound effects on parasite oocyst development. The results show that in addition to protein translation, rRNAs of @entity311 parasites also regulate parasite development and differentiation in a strain-specific manner, which can be explored for controlling parasite transmission.
