Centrosome role in neuronal polarity

Centrosome or MTOC (Microtubule organizing center) is a kind of organelle found in both plant and animal cell which guides the formation of microtubule in the cell. Microtubule array arises from the Centrosome and spreads all over the structure of the normal cell. But in the case of developing neuron, the Centrosome is localized towards one particular neurite and then the microtubules are guided to that neurite which further forms the axon. Centrosome positioning is an important phenomenon in the neuronal polarity because out of all the neurite; one specific axon has to be formed towards the target cell or neuron.

Centrosome positioning takes place at the stage 3 of neuronal polarity, where the Centrosome is found closer to one particular neurite which is said to be the future axon.

After the cell exits from the cell cycle, it forms neurites. And then certain extracellular cues activate the intracellular cues which take the responsibility of Centrosome positioning. Centrosome positioning is the beginning stage of axon specification. 

Structure of Centrosome is made up of two barrel shaped centrioles and a cloud of pericentriolar material that surrounds them. Microtubules are nucleated from the pericentriolar material and form a radial array emanating away from the Centrosome. Nucleation from the Centrosome regulates key features of the microtubules within the array. First, all of the microtubules assemble with their plus ends away from the Centrosome, resulting in a microtubule array of uniform polarity orientation.

This fig shows that the difference between the nonneuronal and neuronal cell’s centrosome activity. The pluripotent precursor cell can give raise to either nonneuronal cell or neuronal cell. In the nonneuronal cell, a portion of the microtubules nucleated by the centrosome are captured by the leading edge of the cell. The motility of the leading edge pulls on the microtubules, and the attached centrosome reacts by relocating in the direction of cell movement. In the neuron, the microtubules are released, and the centrosome is not relocated. Nevertheless, the microtubules are translocated toward the leading edge, which coalesces into a growth cone. The cell body remains stationary and the microtubules translocate into the space between the cell body and the growth cone, which develops into the axon.  

Microtubules destined for the axon are initiated at the centrosome and then released for translocation. Released microtubules are transported through the cytoplasm with their plus ends leading, and many of these are transported into the axon. In the schematic, the white portions of the microtubules represent the part assembled from the centrosome, while the black portions represent the part assembled after release from the centrosome. Plus ends of microtubules are directed away from the centrosome and toward the distal tip of the axon. The space between the slanted lines through the axon represents hundreds of micrometers of axon growth. During transit, the microtubules elongate specifically from their plus ends.

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Posted in: Molecular Neuroscience