Nerve cells can take over the normal cellular protein synthesis machinery in the same way that viruses do when they infect a cell, according to a report published in Nature Neuroscience. When a virus infects a cell, it 'kidnaps' the host cell's ribosomes to boost the production of virus particles. The virus achieves this by using an internal ribosome entry site (IRES), which shuts down and bypasses the normal mechanisms that regulate binding of messenger RNAs to ribosomes.

In a study of egg laying in the sea slug Aplysia, researchers from McGill University observed that the protein production of the egg-laying hormone (ELH) in neurons increased markedly. They found that the 5′ untranslated region of ELH mRNA contained an IRES — which are common in viral mRNAs but not in normal cellular mRNAs.

Wayne Sossin and colleagues also noticed that the stimulus for egg laying caused dephosphorylation of the initiation factor eIF4E. And this single event was sufficient for the cells to switch to IRES-mediated translation. “Egg laying is an important investment for an animal, thus when stimulated to do so, it wants to get it right,” explains Sossin (ScienceDaily, 20th February 2003).

“The discovery reveals ... an unexpected regulatory role of the IRES in nerve cells” according to Nahum Sonenberg, who first discovered the IRES in poliovirus in 1988 (ScienceDaily, 20th February 2003). IRES-regulated protein production might be important in other physiological events, and Sossin predicts that “...IRES regulation may be particularly important at synapses where there are limiting numbers of ribosomes” (Nature Neuroscience).