Repetitive elements in parasitic protozoa

Abstract

A recent paper published in BMC Genomics suggests that retrotransposition may be active in the human gut parasite Entamoeba histolytica. This adds to our knowledge of the various types of repetitive elements in parasitic protists and the potential influence of such elements on pathogenicity.

Figure 1

Effects of repeated sequences on gene expression. (a) An open reading frame (cyan rectangle) with a repetitive region (dark-blue stripes) is transcribed from an upstream promoter (dotted line and arrowhead). 1, Replication slippage leads to a frameshift with a new stop codon (indicated by the cross over the open reading frame). 2, Replication slippage or unequal recombination can increase the number of repeats. (b) A mobile element (magenta gradient shading) is cut from between two genes (cyan and purple rectangles) by transposase (scissors). An error in repair after transposition introduces a chromosome break, which is repaired to give new telomeres (circles). (c) Recombination between homologous mobile elements on two different chromosomes leads to a translocation. (d) Effects of a mobile element (here shown with its own promoter and transcription) on gene expression. 1, An insertion within an open reading frame results in a truncated protein. 2, An insertion at the beginning of an open reading frame can result in large amounts of a fusion protein. 3, The presence of the retroposon or transposon promoter can activate the transcription of a downstream gene, for example by opening the chromatin. 4, Insertion in an opposite orientation results in antisense RNA. 5, Insertion in a 3'-untranslated region can affect mRNA processing, stability or translation. The example shown has normal monocistronic transcription; for kinetoplastids, transcription is polycistronic (not shown).