Scientists Solved the Nagging Mystery of How Genes Emerge From Nothing
To understand the origins of life means to understand the origins of DNA—the information-containing molecule that makes all life possible. The beginning of life on Earth remains a mystery, and for some time, the beginnings of DNA have similarly appeared to arise from nothing. A new study from the University of Helsinki now attempts to fill this notoriously tricky hole in our understanding.
To answer this very big question, University of Helsinki researcher Ari Löytynoja and his team focused on the very small—regulatory genes that encode microRNA molecules, which are only 22 base pairs in length. The human genome is a complicated highway of 20,000 genes capable of constructing life-sustaining proteins, and these protein factories are managed by regulatory genes. The sequences of these regulatory genes (like other RNA and DNA sequences) are palindromic, meaning that genetic code reads the same forwards and backwards.
With the chances of such a sequence occurring at random being extremely small (even for relatively simple microRNA), biologists aren’t exactly sure how the sequences came to be. But by using a computer algorithm to model the gene’s history, Löytynoja and postdoctoral researcher Heli Mönttinen believe they have now discovered how these palindrome pairs arose.
“The whole genome of tens of primates and mammals is known. A comparison of their genomes reveals which species have the microRNA palindrome pair, and which lack it,” Mönttinen said in a press statement. The results of the study were published last month in the journal PNAS. “With a detailed modelling of the history, we could see that whole palindromes are created by single mutation events.”
This newly discovered mechanism for creating de novo (“new”) microRNA can explain roughly one-quarter of the new genes. With evidence of this mechanism found in other evolutionary lineages, the researchers are confident that this process is universal. While this only explains microRNA sequences, this generation of palindromic pairs can be extrapolated to other RNA and DNA sequences as well.
“DNA is copied one base at a time, and typically mutations are erroneous single bases, like mis-punches on a laptop keyboard,” Löytynoja said in a press statement. “We studied a mechanism creating larger errors, like copy-pasting text from another context. We were especially interested in cases that copied the text backwards so that it creates a palindrome.”
Mönttinen said that researchers “now have an elegant model for the evolution of RNA genes,” and the beginnings of an answer to the question of how something came from nothing.
