The trypanosome flagellum as model for parasitology, cell biology and ciliopathies

Cilia and flagella exhibit widely conserved structures and functions across species. In humans, defects in these organelles are responsible for diseases called ciliopathies and many model organisms are used to study them. In this review, we will discuss one of them, the parasite Trypanosoma brucei, which is particularly well-suited to investigate general aspects of cilia and flagella, such as construction or protein localisation. Its flagellum remains present throughout the cell cycle, offering the opportunity to monitor flagellum maintenance and assembly within the same cell. This model organism is very convenient for flagellum live imaging as well as expansion microscopy and ultrastructural studies, including focused ion beam - scanning electron microscopy (FIB-SEM). Efficient tools exist to manipulate the genome, including endogenous tagging, inducible expression system, RNA interference and CRISPR-Cas9 approaches. Here, we review original contributions from studies in trypanosome to our understanding of flagellum construction and intraflagellar transport, as well as the impact of gene mutations in some ciliopathies.