Researchers at the University of Oslo have discovered that nerve fibers form when small vesicles inside the neuron, called endosomes, merge with the cell membrane. The cell membrane is the cell’s outer layer.
The breakthrough was made during microscopy studies at the Centre for Cancer Biomedicine (CCB). CCB is a center of excellence at the University of Oslo (UiO) and Oslo University Hospital.
“Our research uncovered a group of proteins that bring about the process in which vesicles fuse with the cell membrane,” says Professor Harald A. Stenmark, head of the Centre for Cancer Biomedicine.
Neuronal vesicles that come close to the cell membrane are able to fuse with it. The researchers have uncovered a role for a type of motor protein called Kinesin-1, which transports vesicles to the cell membrane. The transport takes place along structures called microtubules, which can be likened to train tracks inside the cell.
“The vesicles themselves form when part of the cell membrane bends inwards and buds off. They do this to take up nutrients from outside the cell, or to bring proteins from the cell membrane inside the cell. The vesicles can either make their way to other vesicles and fuse with them, or they can fuse with the cell membrane. It’s the latter process that we’ve been studying,” says Camilla Raiborg, head of a research group at the CCB.
It turns out that several of the proteins were already known to researchers, as so-called paraparesis proteins, says Stenmark. Faulty versions of these proteins cause the rare disease hereditary spastic paraparesis, in which the legs become weaker and weaker.
“We don’t know exactly how faulty paraparesis proteins lead to damage to nerve fibers,” Stenmark continues. “Our hypothesis is that the nerve fibers require continual maintenance via a process in which small vesicles, endosomes, are carried out to their tips and fuse with the cell membrane. If this mechanism is disrupted, the result may be damage to the nerve fiber,” says Stenmark.
The research group has previously studied ‘receiver proteins,’ or receptors. These are proteins that are able to pick up signals from other cells. The signals usually take the form of small proteins that bind to the receptors. As a result of the binding, the signals are transmitted by the receptors and enter the cell inside small vesicles. The signals are often instructions for the cell to divide.
Cancer involves uncontrolled cell division, so an excess of cell receptors may not be good. It was while studying these receptors and vesicles that researchers discovered that the vesicles also can be used to produce outgrowths from the cells.
The researchers believe that cancer cells may use a mechanism involving such outgrowths to enable them to spread.