Advances in Entamoeba histolytica Biology Through Transcriptomic Analysis

Abstract

A large number of transcriptome-level studies in Entamoeba histolytica, the protozoan parasite that causes amoebiasis, have investigated gene expression patterns to help understand the pathology and biology of the organism. They have compared virulent and avirulent strains in lab culture and after tissue invasion, cells grown under different stress conditions, response to anti-amoebic drug treatments, and gene expression changes during the process of encystation. These studies have revealed interesting molecules/pathways that will help increase our mechanistic understanding of differentially expressed genes during growth perturbations and tissue invasion. Some of the important insights obtained from transcriptome studies include the observations that regulation of carbohydrate metabolism may be an important determinant for tissue invasion, while the novel up-regulated genes during encystation include phospholipase D, and meiotic genes, suggesting the possibility of meiosis during the process. Classification of genes according to expression levels showed that amongst the highly transcribed genes in cultured E. histolytica trophozoites were some virulence factors, raising the question of the role of these factors in normal parasite growth. Promoter motifs associated with differential gene expression and regulation were identified. Some of these motifs associated with high gene expression were located downstream of start codon, and were required for efficient transcription. The listing of E. histolytica genes according to transcript expression levels will help us determine the scale of post-transcriptional regulation, and the possible roles of predicted promoter motifs. The small RNA transcriptome is a valuable resource for detailed structural and functional analysis of these molecules and their regulatory roles. These studies provide new drug targets and enhance our understanding of gene regulation in E. histolytica.

Keywords: Entamoeba histolytica; downstream motifs; encystation; gene expression regulation; highly transcribed genes; promoter motifs; transcriptome; virulence-related.

FIGURE 1

Differentially expressed genes/pathways revealed from transcriptomic date. The major pathways are shown in boxes (with gene in parenthesis). Pathways scored in all studies (purple), three studies (yellow, dotted arrows), two studies (green), single study (pink).

FIGURE 2

Important virulence-related molecules revealed from transcriptomic studies. Cysteine proteases and β-amylase assist in tissue invasion. β-amylase helps in mucus depletion and utilization. AIG1 functions in defense against intestinal bacteria and amoebapores mediate cell lysis. Contact of host cell ligands is facilitated by Gal/GalNAc-inhibitable lectin. Trans membrane kinases (TMKs) and Ras/Rho GTPases are involved in signal transduction. Myb family transcription factors regulate the expression of multiple pathways. Phagocytosis of bacteria/host cells requires the activity of a large number of proteins, including calcium binding proteins (CaBPs) which mediate actin reorganization. Please see text for details.

FIGURE 3

Genes (upper panel) and promoter motifs (M) (lower panel) associated with high/low gene expression. Genes and motifs in purple (Hackney et al., 2007) in green (Naiyer et al., 2019), in white (both studies). The peak position of each motif with respect to AUG is shown; for further details of dispersed motifs please refer to Naiyer et al. (2019).