Initial ciliary assembly in Chlamydomonas requires Arp2/3 complex-dependent endocytosis

Area of Science:

• Cell Biology
• Cytoskeletal Dynamics
• Cilia and Flagella Biology

Background:

• Ciliary assembly and function depend on microtubule dynamics.
• The role of the actin cytoskeleton in ciliogenesis remains incompletely understood.
• Actin networks, nucleated by the Arp2/3 complex, are vital for various cellular processes.

Purpose of the Study:

• To investigate the specific subcellular roles of the Arp2/3 complex-mediated actin cytoskeleton in ciliogenesis.
• To elucidate the mechanisms by which actin contributes to ciliary protein and membrane supply during assembly.
• To characterize the relationship between actin dynamics, endocytosis, and ciliary growth in Chlamydomonas.

Main Methods:

• Utilized the ciliary model organism Chlamydomonas.
• Focused on actin networks nucleated by the Arp2/3 complex.
• Assessed the requirement of the Arp2/3 complex for initial ciliary assembly stages.
• Examined Arp2/3 complex-dependent endocytosis of ciliary proteins.
• Monitored endocytic activity and plasma membrane protein relocalization during ciliary growth.

Main Results:

• The Arp2/3 complex is essential for the early stages of ciliary assembly.
• Arp2/3 complex activity facilitates endocytosis of ciliary proteins and membrane.
• Endocytic activity increases upon induction of ciliary growth.
• Plasma membrane proteins are relocalized to newly forming cilia in an Arp2/3 complex-dependent manner.

Conclusions:

• The Arp2/3 complex-nucleated actin cytoskeleton plays a critical role in supplying proteins and membrane during the initial phase of ciliogenesis.
• Arp2/3 complex-driven endocytosis is a key mechanism for ciliary protein uptake before Golgi-mediated supply is established.
• These findings reveal a novel contribution of the actin cytoskeleton to the fundamental process of ciliary assembly.