A dispensable Plasmodium locus for stable transgene expression.

The ribosomal small subunit locus has been used for transgene expression in the rodent malaria parasites, Plasmodium berghei and Plasmodium yoelii, but this strategy utilizes single crossover integration and is thus prone to reversion by plasmid excision. Targeting of the ribosomal subunit locus may also have a negative effect on oocyst development in the mosquito. In P. berghei, the p230 paralog locus has been used for transgene expression. Here, we show that the P. yoelii S1 locus (sporozoite expressed gene 1) (PY05712) is dispensable and can be used for stable transgene expression throughout the parasite life cycle. P. yoelii s1(-) parasites show no defect in blood stage replication, oocyst formation, sporozoite production, or liver stage development when compared to P. yoelii wildtype parasites. Further, we show that a fluorescent transgene can be stably expressed from this site. This demonstrates that the S1 locus can be utilized for stable expression of heterologous genes in rodent malaria parasites.