Abstract
SUMMARYThe unicellular green alga Chlamydomonas reinhardtii is a biflagellated cell with two actin genes: one encoding a conventional actin (IDA5) and the other encoding a divergent novel actin-like protein (NAP1). Here, we probe how actin redundancy contributes to flagellar assembly. Disrupting a single actin allows complete flagellar assembly. However, when disrupting both actins using latrunculin B (LatB) treatment on the nap1 mutant background, we find that actins are necessary for flagellar growth from newly synthesized limiting flagellar proteins. Under total actin disruption, transmission electron microscopy identified an accumulation of Golgi-adjacent vesicles. We also find that there is a mislocalization of a key transition zone gating and ciliopathy protein, NPHP-4. Our experiments demonstrate that each stage of flagellar biogenesis requires redundant actin function to varying degrees, with an absolute requirement for these actins in transport of Golgi-adjacent vesicles and flagellar incorporation of newly synthesized proteins.
Highlights
And composition of the eukaryotic flagellum are critical for signaling and development in most cell types in the human body
The flagellum is composed of microtubules that extend from a microtubule organizing center known as the basal body, and flagellar assembly requires control of microtubule dynamics
Simultaneous Disruption of All Filamentous Actins within Chlamydomonas Cells To investigate if NAP1 contributes to the actin-dependent flagellar assembly functions previously identified for the conventional actin IDA5 (Avasthi et al, 2014), we obtained a nap1-null mutant strain, which was isolated on the basis of its sensitivity to latrunculin B (LatB), a conventional actin depolymerizing agent (Onishi et al, 2016)
Summary
And composition of the eukaryotic flagellum ( known as the cilium) are critical for signaling and development in most cell types in the human body. Disruption of myosin-Va function stops the formation of the elongated ciliary membrane This new result suggests that actin and myosin-Va are required for microtubule-dependent trafficking of preciliary and ciliary vesicles to the base of the cilia and necessary for ciliogenesis (Wu, et al, 2018). Actin is required for vesicle budding in the endocytic pathway (Girao et al, 2008), which may influence ciliary assembly, as there is a trafficking pathway connecting the endocytic compartments to a vesicular compartment involved in ciliary assembly (Kim et al, 2010) Membrane remodeling for both ciliary exocytosis (Nager et al, 2017) and ciliary resorption are actin-dependent processes (Saito et al, 2017). The current understanding is that actin networks (which potentially block cortical access of basal bodies and ciliary proteins) inhibit cilium formation and elongation in mammalian cells but are required for membrane trafficking to support ciliogenesis. Using an algal model system, we show a broader requirement for filamentous actin in flagellar protein synthesis, trafficking, and incorporation of proteins into an assembling flagellum
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