Evolution of new genes in the laboratory in real time

How new genes arise poses a fundamental biological question. New findings by researchers at Uppsala University and in the US show that it is possible to get new genes to develop in a laboratory environment using a rapid, stepwise process where an already existing gene with multiple functions is initially amplified. The amplified copies are subsequently altered through mutations and develop new specialized functions.
 
In the current study now being published in Science the researchers experimentally tested a specific model (presented in PNAS in 2007) that explains how new genes arise. In the model, an original gene has a weak secondary activity alongside its strong normal primary activity. If this extra activity becomes important, for example because of changes in the organism’s environment, the number of copies of the original gene can increase very rapidly in the organism’s population. Examples of environmental changes might be that the organism is exposed to a toxic substance (such as antibiotics, herbicides, insecticides) that must be disarmed in some way for the organism to survive. The rise in the number of gene copies also increases the probability that mutations will be selected to improve the secondary function. Once these mutations have occurred, the extra copies can disappear, ultimately leaving two genes, one original gene with its normal function and a gene copy with enhanced secondary function.
 
Dr. Joakim Näsvall tested the model in the laboratory by creating a bi-functional gene involved in the synthesis of two amino acids, tryptophan and histidine. Bacteria with this gene were then grown in a growth medium that lacked both amino acids, which led to selection for gene amplification of up to 20 copies of the same gene. Later, mutations arose that specialized different gene copies to be better at either tryptophan synthesis or histidine synthesis, or in some cases better at both reactions.
 
- Joakim Näsvall’s convincing experimental findings provide strong support for our previously proposed model. They show how new genes can arise after just a few thousand generations of bacterial growth, corresponding to about one year in real time, in the laboratory if an appropriate selection pressure is in place, says professor Dan Andersson, who directed the study.
 
The research was funded by the Swedish Research Council.
For information about this research at Uppsala University, please contact Dan Andersson, e-mail: Dan.Andersson@imbim.uu.se, mobile: +46 (0)70-1679077 or Joakim Näsvall, e-mail: Joakim.Nasvall@imbim.uu.se, mobile: +46 (0)70-6972236