Endoplasmic reticulum continuity in the protozoan parasite Entamoeba histolytica

Abstract

Entamoeba histolytica has been described as an early branching eukartoric parasite based on the lack of organelles such as mitochonsoria and peroxisomes, and on morphologic studies that concluded it possesses a vesicular endoplasmic reticulum (ER) and Golgi complex. However, a recent study from our laboratory showed that the E. histolytica ER is continuous by using an ER-targeted green fluorescent protein fusion protein and photoblaching experiments. We proposed that the vesicular ER seen earlier was likely an artifact of fixation. We now report data using an alternative fixation protocol that preserves the continuous ER morphology. These data confirm that the vesicular ER reported earlier was indeed a fixation artifact; furthermore, since we observed the same ER srtucture when staining for the native antigen HSP-70 in wild type amebae, the data provide direct evidence that the continuous ER morphology we reported is correct. This work has important implications for cell biologists studying E. histolytica virulence, emphasizes the frequent need to reassess assumptions based on published data, and provides additional evidence that E. histolytica actually diverged relatively late in evolution and that many of its unusual features are likely due to loss of features during adaptation to its ecological niche.