Myosin-independent cytokinesis in Giardia utilizes flagella to coordinate force generation and direct membrane trafficking

Abstract

Devoid of all known canonical actin-binding proteins, the prevalent parasite Giardia lamblia uses an alternative mechanism for cytokinesis. Unique aspects of this mechanism can potentially be leveraged for therapeutic development. Here, live-cell imaging methods were developed for Giardia to establish division kinetics and the core division machinery. Surprisingly, Giardia cytokinesis occurred with a median time that is ∼60 times faster than mammalian cells. In contrast to cells that use a contractile ring, actin was not concentrated in the furrow and was not directly required for furrow progression. Live-cell imaging and morpholino depletion of axonemal Paralyzed Flagella 16 indicated that flagella-based forces initiated daughter cell separation and provided a source for membrane tension. Inhibition of membrane partitioning blocked furrow progression, indicating a requirement for membrane trafficking to support furrow advancement. Rab11 was found to load onto the intracytoplasmic axonemes late in mitosis and to accumulate near the ends of nascent axonemes. These developing axonemes were positioned to coordinate trafficking into the furrow and mark the center of the cell in lieu of a midbody/phragmoplast. We show that flagella motility, Rab11, and actin coordination are necessary for proper abscission. Organisms representing three of the five eukaryotic supergroups lack myosin II of the actomyosin contractile ring. These results support an emerging view that flagella play a central role in cell division among protists that lack myosin II and additionally implicate the broad use of membrane tension as a mechanism to drive abscission.

Roles of end‐binding 1 protein and gamma‐tubulin small complex in cytokinesis and flagella formation of Giardia lamblia

“…Thus, it is possible that the cytokinesis defects in the Glγ‐TuSC‐depleted or GlEB1‐depleted cells are caused from malfunction of the four pairs of flagella. This idea is in a good agreement with the study of Hardin et al (). Through in vivo image analysis of Giardia cells expressing fluorescence‐labeled MTs, they assigned the role in cytokinesis to all of four pairs of flagella.…”

“…Thus, this investigation showed for the first Zhou & Li, 2015). In G. lamblia, flagella had been shown to play a role in cytokinesis through knockdown of paralyzed flagella 16 protein, which is associated with the central pair MTs of the flagella (Hardin et al, 2017).…”

“…Decreasing the expression of T. brucei γ‐tubulin or T. brucei GCPs (TbGCP2 and TbGCP3) by RNA interference also resulted in axonemes losing the central pair MTs and defects in the biogenesis of new flagellum (McKean, Baines, Vaughan, & Gull, ; Zhou & Li, ). In G. lamblia , flagella had been shown to play a role in cytokinesis through knockdown of paralyzed flagella 16 protein, which is associated with the central pair MTs of the flagella (Hardin et al, ).…”

“…Effect of knockdown of Glγ‐tubulin, GlGCP2, and GlGCP3 on cytokinesis was monitored as described (Hardin et al, ). Various G. lamblia trophozoites (controls, and the cells treated with anti‐Glγ‐tubulin, anti‐GlGCP2, and anti‐GlGCP3 morpholino) were grouped by the following phenotypes: disorganized for cytokinesis, defective in furrow formation, disable in cytokinesis, and failed abscission.…”

“…Effect of knockdown of Glγ-tubulin, GlGCP2, and GlGCP3 on cytokinesis was monitored as described (Hardin et al, 2017). Various G.…”