Theory on evolution of essential genes is overturned

A gene passed on by fathers that plays a vital role in helping fertilised eggs to develop into adults has helped scientists overturn the idea that essential genes have always been part of the genetic makeup of a species.

The research, published in the journal Current Biology, shows that an essential ‘paternal effect’ gene was created only recently in the evolutionary history of the fruit fly, Drosophila.

This finding is remarkable because it shows that new genes with new functions - including essential functions - can evolve at any time.

The researchers made the discovery as part of a project to produce the first molecular genetic characterisation of a paternal effect gene. Paternal effect genes are important because without them a fertilised egg cannot develop into an adult. Similar genes are most likely present in other animals, including humans.

Using molecular techniques, the researchers found that the Drosophila paternal effect gene they were characterising was only present in the melanogaster sub-group of fruit fly, but its progenitor, or ancestor, was present in all of the different sub-groups.

Using statistical information about the rate at which genes evolve, the researchers worked out that the gene was only about 1-2 million years old, and much younger than the majority of the genes in the remainder of the fruit fly genome.

This finding, that an essential gene has a relatively recent origin, overturns the conventional notion that genes with vital functions must have been created a long time ago, but raises important questions about why and how this particular gene evolved.

“This discovery really changes our concept of how new gene function can evolve, which is a major issue for evolutionary biology,” said Dr Tim Karr from the University of Bath, who made the discovery with colleagues in the Centre de Genetique Moleculaire et Cellulaire in France and the University of Chicago.

“It is remarkable to think that through a range of random, naturally-occurring genetic changes over a few million years, a new essential gene has evolved. Obviously other species of fruit fly don't need this gene but they may have other genes that serve a similar function. At first the gene may have conveyed some as yet unknown benefit that eventually became essential during the course of evolution. It could even have been involved in the early processes leading to speciation of this group of fruit flies,” said Dr Karr.

Dr Steve Dorus from the University of Chicago, who collaborated on the project, will be joining the Karr laboratory at the University of Bath this month to continue studies on this, and other paternal genes.

“The fact that this essential, newly-evolved gene is a male factor that is required for successful embryo development after fertilisation makes it all the more interesting. Paternal effect genes have only recently become the subject of scientific investigation, and the genetic characterisation of this gene will help further investigations in this area,” said Dr Karr.

“I would be very surprised if there were not more examples of paternal effect genes spread throughout the animal kingdom. Because we know so much about the relatively simple genetic makeup of the fruit fly, it is yet another example of where Drosophila can help us understand important genetic processes throughout the animal kingdom, including humans.”

The research was funded by the Royal Society.