Epigenetic control of the variable expression of a Plasmodium falciparum receptor protein for erythrocyte invasion.

Plasmodium falciparum can invade erythrocytes by redundant receptors, some of which have variable expression. A P. falciparum clone Dd2 requiring erythrocyte sialic acid for invasion can be switched to a sialic acid-independent progeny clone Dd2NM by growing the Dd2 clone with neuraminidase-treated erythrocytes. The RH4 gene is transcriptionally up-regulated in Dd2NM compared to Dd2, despite the absence of DNA changes in and around the gene. We determined the epigenetic modifications around the transcription start site (TSS) at the time of expression of RH4 in Dd2NM (44 h) and at an earlier time when RH4 is not expressed (24 h). At 44 h, the occupancy of the +1 nucleosome site downstream of the TSS of the active RH4 gene in Dd2NM was markedly reduced compared to Dd2; no difference was observed at 24 h. At 44 h, histone modifications associated with up-regulation were positively correlated to the active RH4 gene of Dd2NM compared to Dd2; no differences were observed at 24 h. Histone H3K9 trimethylation (a marker for silencing) was higher in Dd2 than Dd2NM along the 5'-UTRs of the RH4 gene at both 44 and 24 h. Our data indicate that the failure of Dd2 to express the sialic acid-independent invasion receptor gene RH4 is associated with the epigenetic silencing mark H3K9 trimethylation present throughout the cycle.