'Selfish DNA' driving insecticide resistance (4/2/2007)

Transposable elements, sometimes called ‘selfish DNA’, can be responsible for insecticide resistance, according to scientists from the Universities of Exeter, Bath and Melbourne. Transposable elements (TEs) can ‘jump around’ the genome and cause mutations by inserting into the coding regions of genes and disrupting or altering, and in this case increasing, gene function.

A study published in Genetics and funded by the Biotechnology and Biological Sciences Research Council (BBSRC), which focuses on the fruit fly Drosophila melanogaster, sheds new light on the mechanics of insecticide resistance. The research team found that insecticide resistance in this species is due to the up-regulation of one particular cytochrome P450 gene (Cyp6g1). P450s are known for their role in the detoxification of foreign materials and this genetic adaptation, which occurred as a result of a single transposable element insertion, has now spread throughout the entire species.

Professor Richard ffrench-Constant of the University of Exeter said:

"We believe this adaptation has spread to between 80 and 100% of fruit flies worldwide in the space of about forty years. This is an amazing example of how transposable element insertions, which initially occur purely by chance, can contribute to the adaptation and evolution of an entire species."

This research represents a rare example of scientists fully characterising the effects of a TE mutation at molecular level. Scientists are only just beginning to understand the mechanics of TEs, which are now known to play a role in genome evolution in many species, including humans. Scientists have only recently identified resistance mechanisms involving TEs in insect populations. Unusually in this example the TE is expressed in exactly the same pattern as the resistance-associated gene itself, suggesting that the overlap of the two expression patterns combines in an additive effect, leading to over-expression of the P450 gene.

The new gene confers resistance to the former best seller DDT (now withdrawn due to its habit of persisting in the environment) and also to a newer generation of insecticides, the current best sellers the neonicotinoids.

"If a gene like this were to appear in a real pest it would be disastrous," continued Professor ffrench-Constant, "because the usual trick of picking another pesticide and hoping that resistance goes away simply will not work".

The researchers now aim to analyse TE insertions in other species to further investigate the molecular basis of adaptation.

Note: This story has been adapted from a news release issued by The University of Exeter

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