Software helps to find out why "jumping genes" are activated


Jumping genes, so-called transposons, reproduce as parasites in the genome. This selfish behavior can be an evolutionary advantage for the organism or harm it. There is still a debate about the factors controlling the activity of transposons.

Image: A circular diagram; Copyright: Robert Kofler/Vetmeduni Vienna

Using the new tool PoPoolationTE2 allows for calculating the frequency of transposable elements in Pool-Seq sequencing reactions; Copyright: Robert Kofler/Vetmeduni Vienna

Comparisons between populations could shed an answer on this but have been biased due to technical problems. The software PoPoolationTE2 developed by the Institute of Population Genetics at Vetmeduni Vienna enables an unbiased analysis for the first time and determines the frequency of transposons. This might also be useful for cancer research and neurology. The software was presented in the renowned journals Molecular Biology and Evolution.

The genome is not a fixed code but flexible. It allows changes in the genes. Transposons, however, so-called jumping genes, interpret this flexibility in a much freer way than "normal" genes. They reproduce in the genome and chose their position themselves. Transposons can also jump into a gene and render it inoperative. Thus, they are an important distinguishing mark for the development of different organisms.

However, it is still unclear how jumping genes developed and what influences their activity. "In order to find out how, for instance, climate zones influence activity, we must be able to compare the frequency of transposons in different populations - in different groups of individuals," explained bioinformatician Robert Kofler from the Institute of Population Genetics at the University of Veterinary Medicine, Vienna. But this frequency has not yet been determined precisely.

Transposons are detected by DNA sequencing. But this detection cannot be carried out for every single member of a population. "At the moment, this would go beyond the available resources regarding finance and amount of work. The only - and much cheaper - option is to analyze an entire population in one reaction," explained last author Christian Schlötterer. This method, which he has established using the example of fruit flies, is called Pool-Seq. It is also routinely applied to detect transposons. Existing analysis programs, however, could not provide a precise result in this case. So far, each analysis has been biased by different factors such as the sequencing depth and the distance between paired reads.

For this purpose, Kofler developed the new software PoPoolationTE2. "If we sequence entire populations, each reaction provides a different result. The number of mixed individuals is always the same, but the single individuals differ," explained Kofler. Furthermore, technical differences in the sample processing, among others, have influenced the analysis so far. PoPoolationTE2 is not affected by these factors. Thus, questions about the activity of transposons can be answered precisely for Pool-Seq reactions.

"The unbiased detection of transposon abundance enables a low-price comparison of populations from, for instance, different climate zones. In a next step, we can find out if a transposon is very active in a particular climate zone," said Kofler. In principle, the bioinformatician has developed this new software for Pool-Seq. But as this method is also applied in medical research and diagnosis, the program is also interesting for cancer research or the detection of neurological changes since transposons also occur in the brain.

Lab experiments can indicate the factors influencing transposons. Last author Schlötterer explained these factors referring to an experiment with fruit flies: "We breed a hundred generations per population and expose them to different stimuli. We sequence at every tenth generation and determine if a stimulus has influenced the activity of the transposons. Thus, we can describe the activity of transposons in fast motion, so to say." If the abundance is low, the scientists assume that the transposons are only starting to become more frequent. If a transposon reproduces very quickly in a particular population, this is called an invasion. If a jumping gene is detected in an entire population and not in another one, it could have been positively selected.; Source: Vetmeduni Vienna

More about Vetmeduni Vienna at: