Myelin accelerates stimuli: Shedding light on the mechanisms of myelin formation in the central nervous system

This is made possible by an insulating sheath of myelin that forms at certain intervals around the axonal extensions of nerve cells that specialize in the transmission of stimuli. In disorders such as multiple sclerosis or leukodystrophy, the formation or function of the myelin is disturbed.

Previously, the molecular mechanisms of myelin formation were not well understood. Two projects undertaken by the Department of Molecular Cell Biology of the Faculty of Biology at the Johannes Gutenberg University in Mainz have now made a significant contribution towards understanding these complex cellular processes.

In simple terms, signals transmitted during saltatory conduction jump from one non-myelinated area (the nodes of Ranvier) to another, which enormously increases the speed of transmission. Myelin is formed in the central nervous system when oligodendrocytes – a specific type of brain cell – wrap their cellular extensions around the axons of the nerve cells several times, thus forming a compact stack of cellular membranes. The team of scientists under Professor Jacqueline Trotter from the Mainz Department of Molecular Cell Biology have now been able to show which mechanisms contribute towards the formation of an intact myelin sheath and how the nerve cells control the place and time of myelin production.

Reported in a paper published in the Journal of Cell Science was the fact that an endocytic myelin protein recycling system is important for the specific formation of myelin domains. During this process, proteins are first transported to the surface of the cells. They are then reabsorbed into the cell by means of endocytosis and sorted into various membrane domains, which subsequently return to the cell surface. This 'membrane conversion' appears to be necessary for the correct formation of an intact myelin sheath.

Also reported in the prestigious Journal of Cell Biology was the discovery of a new transmission pathway, which originates with the interaction between a neuronal and oligodendroglial surface molecule, involves the activation of the signal molecule essential for myelinization and leads to the local translation of a main myelin protein into an oligodendrocyte. These results have opened up the possibility of developing a new technique of influencing nerve cells and determining where and when myelin is to be synthesized, while also demonstrating the significant role played by both types of cell in the formation of a basis for efficient stimulus transmission within the central nervous system.