Mechanism that Controls Production of Egg-Laying Hormone

A recent study has found that protein production during egg laying in the sea slug Aplysia is mediated by a mechanism similar to that used by viruses when they take control of a cell's ribosomes. The study appeared in the February 18, 2003, online edition of Nature Neuroscience.

Viruses seize control of the cell's protein synthetic apparatus (the ribosomes) by using an internal ribosome entry site (IRES), which shuts down and bypasses the normal mechanisms that regulate binding of messenger RNAs to ribosomes. The cells stop making their normal proteins and switch to production of viral proteins. These IRES sites are normal features of viral RNA but are very rare in the RNA of normal cells.

In the current study, investigators from McGill University (Montreal, Canada) observed that during egg laying, Aplysia produced massive amounts of egg-laying hormone (ELH). Furthermore, the ELH messenger RNA was found to contain an IRES. After egg laying takes place, nerve cells producing ELH switched from the normal cellular mechanism of protein production to one that used the IRES. This switch allowed for massive amounts of ELH protein to be produced at the expense of other cellular proteins, mimicking the behavior of viruses during infection of a host cell.

"Egg laying is an important investment for an animal, thus when stimulated to do so, it wants to get it right,” explained senior author Dr. Wayne Sossin, an investigator at McGill University's Montreal Neurological Institute. "In order to do this, the cell must make a lot of ELH protein in a short period of time to signal the release of eggs. One way to do this is to temporarily stop making other proteins and concentrate on making one particular protein – in this instance, the ELH.”



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