Stage-specific ribosomal RNA expression switches during sporozoite invasion of hepatocytes.

Two structurally distinct ribosomal RNAs (rRNAs) occur in different developmental stages of malaria parasites. One point at which the transition from one type to the other is found shortly after sporozoites invade hepatocytes, the first stage of parasite development in the mammalian host. The invasion in itself appears necessary but insufficient to trigger the rRNA transition. The progression of events involved in the synthesis of a new type ribosome is tied to the fate of the invading parasite. Interestingly, the switch also occurs in irradiated sporozoites. The new rRNAs produced are processed to the mature size, indicating that rRNA transcription and processing remain normal in the attenuated parasites. These results have implications for monitoring antimalaria vaccine candidates and drug efficacy.