Abstract
The human intestinal pathogen Entamoeba histolytica has a number of virulence factors which can cause damage to the host. Transcriptional silencing of the gene coding for one of its major toxic molecules, the amoebapore (Ehapβa), occurred following the transfection of amoebic trophozoites with a plasmid containing the 5β² promoter region of Ehapβa as well as a truncated segment of a neighboring, upstream SINE1 element that is transcribed from the opposite strand. Silencing was dependent on the presence of the truncated SINE1 sequences. Small amounts of short (βΌ140 n), ssRNA molecules with homology to SINE1 were detected in the silenced amoeba but no siRNA. The silenced Ehapβa gene domain had a chromatin modification indicating transcriptional inactivation without any DNA methylation. Removal of the plasmid did not restore transcription of Ehapβa. Transcription analysis by microarrays revealed that a number of additional genes were silenced and some were also upβregulated. Transfections of amoeba which already had a silenced Ehapβa, with a plasmid containing a second gene ligated to the 5β² upstream region of Ehapβa, enabled the silencing, inβtrans, of other genes of choice. The nonvirulent phenotype of the geneβsilenced amoeba was demonstrated in various assays and the results suggest that they may have a potential use for vaccination. Β© 2008 IUBMB IUBMB Life, 60(9): 598β604, 2008