cytosolic ciliogenesis

Definition

Target type: biologicalprocess

The process in which an axoneme is exposed entirely or partially to the cytoplasm or by which the cytoplasmic portion is assembled or extended. Cytosolic ciliogenesis can occur following compartmentalized ciliogenesis, in which the cilium is formed within a compartment separated from the cytoplasm. [PMID:25447994, PMID:26654377]

Cytosolic ciliogenesis is a complex process that involves the assembly of a microtubule-based structure, the cilium, from the cytoplasm of a cell. This process is crucial for a wide range of cellular functions, including sensory perception, signal transduction, and fluid flow.

**1. Initiation:**
* The process begins with the formation of a basal body, a specialized structure derived from a centriole. The basal body acts as a template for the growing cilium.
* At the site of the basal body, a protein complex called the "ciliary necklace" assembles, which is responsible for regulating the entry and exit of proteins to the developing cilium.

**2. Microtubule Assembly:**
* Microtubules are the building blocks of the cilium. They are formed from α- and β-tubulin dimers that polymerize into protofilaments.
* These protofilaments associate laterally to form 13 protofilament microtubules.
* The microtubules are organized into a 9 + 2 arrangement, with nine outer microtubule doublets surrounding a central pair.
* Microtubules are anchored at the basal body and grow outward towards the tip of the cilium.

**3. Ciliary Membrane Formation:**
* The ciliary membrane, which encloses the cilium, is derived from the plasma membrane.
* It is transported to the growing cilium by small vesicles that bud off from the plasma membrane.
* As the ciliary membrane grows, it incorporates specific proteins and lipids that are essential for ciliary function.

**4. Cargo Transport:**
* Proteins, lipids, and other cargo molecules are transported into the cilium via the intraflagellar transport (IFT) system.
* IFT is a specialized system that uses motor proteins and microtubule tracks to move cargo bidirectionally along the ciliary microtubules.
* IFT is essential for the assembly and maintenance of the cilium.

**5. Ciliary Length Control:**
* The length of the cilium is tightly regulated.
* The cilium grows until it reaches a specific length, at which point further growth is arrested.
* This length control mechanism is thought to involve feedback loops that monitor ciliary length and regulate the activity of IFT.

**6. Ciliary Function:**
* Once the cilium is assembled, it can perform its specialized functions.
* These functions include:
* Sensory perception: Cilia can detect various stimuli, such as light, sound, and chemicals.
* Signal transduction: Cilia can relay signals from the external environment to the cell interior.
* Fluid flow: Cilia can generate fluid flow, as seen in the respiratory tract and the brain ventricles.

**7. Ciliary Disassembly:**
* In some cases, cilia can be disassembled, which is a process that is controlled by cellular signaling pathways.
* Disassembly of cilia can occur in response to environmental changes or during cell division.

Cytosolic ciliogenesis is a highly regulated and dynamic process that is essential for a wide range of cellular functions.'
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