How does memory work? The further we seem to dive in, the more questions we stumble upon about how the function of memory first evolved. Scientists made a key breakthrough with the identification of the Arc protein in 1995, observing how its role in the plastic changes in neurons was critical to memory consolidation.
This protein is already a big deal, but the Arc picture just got a lot more interesting. In a study published Thursday in the journal Cell, a team of researchers at the University of Utah, the University of Copenhagen in Denmark, and MRC Laboratory of Molecular Biology in Cambridge, UK, argue that Arc took its place in the brain as a result of a random chance encounter millions of years ago. Similar to how scientists say the mitochondria in our cells originated as bacteria that our ancient ancestors’ cells absorbed, the Arc protein seems to have started as a virus.
Much as a virus infects host cells, Arc can deliver genetic material to brain cells.
The researchers knew they were onto something when they captured an image of Arc that looked an awful lot like a viral capsid, the isohedral protein coat that encapsulates a virus’s genetic material for delivery to host cells during infection.
“At the time, we didn’t know much about the molecular function or evolutionary history of Arc,” says study coauthor Jason Shepherd, an assistant professor of neurobiology, anatomy, biochemistry, and ophthalmology at the University of Utah, in a statement. Shepherd has studied Arc for 15 years. “I had almost lost interest in the protein, to be honest. After seeing the capsids, we knew we were onto something interesting.”
The main issue that challenges neuroscientists’ understanding of memory is that proteins don’t last very long in the brain, even though memories last nearly a lifetime. So for memories to remain, there must be plastic changes, meaning that neuron structures actually have to change as a result of memory consolidation.
This is where Arc…