Identification and characterisation of the cryptic Golgi apparatus in Naegleria gruberi

Abstract

Although the Golgi apparatus has a conserved morphology of flattened stacked cisternae in most eukaryotes, it has lost the stacked organization in several lineages, raising the question of what range of morphologies is possible for the Golgi. In order to understand this diversity, it is necessary to characterise the Golgi in many different lineages. Here we identify the Golgi apparatus in Naegleria, the first description of an unstacked Golgi organelle in a non-parasitic eukaryote, other than fungi. We provide a comprehensive list of Golgi-associated membrane trafficking genes encoded in two species of Naegleria and show that nearly all are expressed in mouse-passaged N. fowleri cells. We then study distribution of the Golgi marker NgCOPB by fluorescence, identifying membranous structures that are disrupted by Brefeldin A treatment, consistent with Golgi localisation. Confocal and immuno-electron microscopy reveals that NgCOPB localizes to tubular membranous structures. Our data identify the Golgi organelle for the first time in this major eukaryotic lineage, and provide the rare example of a tubular morphology, representing an important sampling point for the comparative understanding of Golgi organellar diversity.