Nanoarchitecture of the ventral disc of Giardia intestinalis as revealed by high-resolution scanning electron microscopy and helium ion microscopy

The parasitic protozoan Giardia intestinalis, the causative agent of giardiasis, presents a stable and elaborated cytoskeleton, which shapes and supports several intracellular structures, including the ventral disc, the median body, the funis, and four pairs of flagella. Giardia trophozoite is the motile form that inhabits the host small intestine and attaches to epithelial cells, leading to infection. The ventral disc is considered one important element of adhesion to the intestinal cells. It is adjacent to the plasma membrane in the ventral region of the cell and consists of a spiral layer of microtubules and microribbons. In this work, we studied the organization of the cytoskeleton in the ventral disc of G. intestinalis trophozoites using high-resolution scanning electron microscopy or helium ion microscopy in plasma membrane-extracted cells. Here, we show novel morphological details about the arrangement of cross-bridges in different regions of the ventral disc. Results showed that the disc is a non-uniformly organized structure that presents specific domains, such as the margin and the ventral groove region. High-resolution scanning electron microscopy allowed observation of the labeling pattern for several anti-tubulin antibodies using secondary gold particle-labeled antibodies. Labeling in the region of the emergence of the microtubules and supernumerary microtubules using an anti-acetylated tubulin antibody was observed. Ultrastructural analysis and immunogold labeling for gamma-tubulin suggest that disc microtubules originate from a region bounded by the bands of the banded collar and merge with microtubules formed at the perinuclear region. Actin-like filaments and microtubules of the disc are associated, showing an interconnection between elements of the cytoskeleton of the trophozoite.