Nuclear Movements in Neurons

Neuronal migration is an important step in the formation of neural networks. Neuronal migration proceeds in a saltatory fashion, repeating two phases that underlie the movement. There is a rapid extension stabilizing first and followed by the nucleus, and other organelles are translocated. These two periods are not typically synchronized and utilize mechanisms that are somehow loosely linked.

Nuclear Movements

Neuronal migration is a complex event that requires the translocation of the nucleus. The nucleus is by far the most oversized cargo of the cell, with a volume approximately equal to the entire extranuclear volume of the cytoplasmic contents. Two special events underlie nuclear movement: the first one is the centrosome movement into the leading process, and another is the movement of the nucleus. The mechanism of nuclear movement in neurons indicates the centrosome participate in driving nuclear migration. The overwhelming size of the nucleus and its asynchronous translocation events show that molecular determinants of its movement may be distinct from pathways that direct neurite outgrowth or other phases of neuronal migration.

Fig.1 Steps in neuronal migration. (Marin, 2006)

Regulation of Nuclear Movements

Regulation of nuclear movement is a critical event in neuronal migration during brain development. Newborn neurons could migrate to their function sites by squeezing their most oversized cargo, the nucleus, through the crowded neural tissue. The mechanism with many intricate interplays propels nuclear movements in neurons. They include microtubules, actin, and their associated motor proteins, cytoplasmic dynein, and myosin. The model of nuclear movement in which the PARD6a-PKCz complex participates in the forward movement of the centrosome; meanwhile, the dynein motor complex participates in the translocation of the nucleus. The translation of the nucleus in migrating neurons requires fine coordination between the movements directed by the actin cytoskeleton and the motor complex.

• Actin-Myosin Based Nuclear Translocation

The nucleus is always translocated by both actomyosin traction forces and microtubule motors. Actomyosin probably has a role in nuclear translocation and driving the nucleus towards the centrosome by generating a pushing force behind the nucleus.

Fig.2 Actomyosin-based nuclear translocation in neurons. (Nakazawa, 2020)

• Microtubule Based Nuclear Translocation

Microtubule is essential regulators of nuclear movement. Generally speaking, the microtubule exerts forces to the nuclear envelope via assembly with the LINC complex, thereby precisely steering the nucleus into the correct direction and position. Dynein might mediate the movement of both the centrosome and the nuclear. It is notable that dynein and kinesin are not simply segregated into exclusive traffic lanes but can synergistically drive one-way nuclear movement along microtubules.

Fig.3 Microtubule-based nuclear translocation in neurons. (Nakazawa, 2020)

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References

1. Marin, O.; et al. Neurons in motion: same principles for different shapes? Trends in neurosciences. 2006, 29(12), 655-661.
2. Nakazawa, N.; Kengaku, M. Mechanical regulation of nuclear translocation in migratory neurons. Frontiers in cell and developmental biology. 2020, 8, 150.