Species-specific regulation and switching of transcription between stage-specific ribosomal RNA genes in Plasmodium berghei.
Malaria parasites (Plasmodium spp.) differentially express structurally distinct sets of rRNA genes in a stage-specific manner. The four rRNA genes of the rodent malaria parasite, P. berghei, form two classes of 2 units that are genetically unlinked and termed A-type and S-type. Through Northern analysis and in situ hybridization, expression of the units was demonstrated in synchronized parasite preparations covering the developmental pathway from the initiation of the blood-stage asexual cycle to the production of mature ookinetes. A-type units were transcribed in direct response to cell growth in bloodstage asexual parasites yet were differentially regulated during male (inactive) and female (active) gametocytogenesis. S-type expression was not confined solely to the mosquito stages and exhibited a finite period of expression in a subset of bloodstage trophozoites that was significantly elevated in gametocyte-producing parasites. Unlike in the human parasite, P. falciparum, there was no evidence for accumulation of precursor forms of the S-type transcripts in gametocytes. No significant rRNA transcription was observed in cultured, fertilized ookinetes until approximately 20 h of development when S-type transcription was initiated. The results further demonstrate that in Plasmodium the expression of the different rRNA units is linked to developmental progression but in a species-specific manner.
Waters
A P
AP
Department of Parasitology, University of Leiden, Postbus 9605, 2300RC Leiden, The Netherlands. Waters@rullf2.leidenuniv.nl
van Spaendonk
R M
RM
Ramesar
J
J
Vervenne
R A
RA
Dirks
R W
RW
Thompson
J
J
Janse
C J
CJ
D000818:Animals; D015152:Blotting, Northern; D004275:DNA, Ribosomal / Q000737:chemistry; D005260:Female; D006801:Humans; D017403:In Situ Hybridization; D008297:Male; D008954:Models, Biological; D010962:Plasmodium berghei / Q000235:genetics*; D015347:RNA Probes / Q000378:metabolism; D012335:RNA, Ribosomal / Q000235:genetics*; D014158:Transcription, Genetic
D004275:DNA, Ribosomal; D015347:RNA Probes; D012335:RNA, Ribosomal