Conversion of anterograde into retrograde trains is an intrinsic property of intraflagellar transport.

Cilia or eukaryotic flagella are microtubule-based organelles found across the eukaryotic tree of life. Their very high aspect ratio and crowded interior are unfavorable to diffusive transport of most components required for their assembly and maintenance. Instead, a system of intraflagellar transport (IFT) trains moves cargo rapidly up and down the cilium (Figure 1A).1-3 Anterograde IFT, from the cell body to the ciliary tip, is driven by kinesin-II motors, whereas retrograde IFT is powered by cytoplasmic dynein-1b motors.4 Both motors are associated with long chains of IFT protein complexes, known as IFT trains, and their cargoes.5-8 The conversion from anterograde to retrograde motility at the ciliary tip involves (1) the dissociation of kinesin motors from trains,9 (2) a fundamental restructuring of the train from the anterograde to the retrograde architecture,8,10,11 (3) the unloading and reloading of cargo,2 and (4) the activation of the dynein motors.8,12 A prominent hypothesis is that there is dedicated calcium-dependent protein-based machinery at the ciliary tip to mediate these processes.4,13 However, the mechanisms of IFT turnaround have remained elusive. In this study, we use mechanical and chemical methods to block IFT at intermediate positions along the cilia of the green algae Chlamydomonas reinhardtii, in normal and calcium-depleted conditions. We show that IFT turnaround, kinesin dissociation, and dynein-1b activation can consistently be induced at arbitrary distances from the ciliary tip, with no stationary tip machinery being required. Instead, we demonstrate that the anterograde-to-retrograde conversion is a calcium-independent intrinsic ability of IFT.

Lis1 co-localizes with actin in the phagocytic cup and regulates phagocytosis.

Phagocytosis, the ingestion of solid particles by cells is essential for nutrient uptake, innate immune response, antigen presentation and organelle homeostasis. Here we show that Lissencephaly-1 (Lis1), a well-known regulator of the microtubule motor dynein, co-localizes with actin at the phagocytic cup in the early stages of phagocytosis. Both knockdown and overexpression of Lis1 perturb phagocytosis, suggesting that Lis1 levels may be regulated during particle engulfment to facilitate remodeling of actin filaments within the phagocytic cup. This requirement of Lis1 is replicated in mouse macrophage cells as well as in the amoeba Dictyostelium, indicating an evolutionarily conserved role for Lis1 in phagocytosis. In support of these findings, Dictyostelium cells overexpressing Lis1 show defects in migration possibly caused by dysregulated actin. Taken together, Lis1 localizes to the phagocytic cup and influences the actin cytoskeleton in a manner that appears important for the uptake of solid particles into cells.