At the very foundation of modern biology lies the idea that the majority of genes encoded in DNA are transcribed into smaller RNA molecules which are then translated into proteins. DNA is often said to be the blueprint of life and proteins are described as its building blocks. RNA is seen as a simple messenger between those two functions
However recent research suggests that it might be more accurate to compare RNA to an engineer. A vast part of DNA does not code for proteins, but instead produces a plethora of small RNA molecules which seem to regulate the genome through a variety of mechanisms. By modulating the levels of messenger RNA in the cell (the RNA that actually gets translated into proteins), those small RNA molecules are able to dramatically alter the ways in which it operates. Like an engineer, they allow the cell to interpret its plans, modifying it where necessary.
There is a large variety of non-coding RNA molecules which work toward repressing the expression of target mRNAs, such as piwi interacting RNA (piRNA) or small interfering RNA (siRNAs). One of the most recent regulatory RNA discovered is called micro RNA (miRNA). miRNAs are single-stranded small RNA molecules (about 23 nucleotide long) which regulate gene expression by silencing the mRNA already present in the cell. They bind complementarily to the single stranded mRNA molecule at the 3’UTR (untranslated regions) sites. The miRNA sequence does not need to match its target 3’UTR perfectly in order to have an effect, but a better match will lead to a more potent effect. Their mechanism of action is still being debated, but current models favour the idea that they can work along with other proteins to degrade their target mRNA.
Shedding light on the mechanism of miRNA action is crucial if we want to understand the vastly complex problem of gene regulation. For example the Alonso lab at the University of Sussex tries to understand the ways in which miRNAs can control the development of complex tissues such as the nervous system in the fruit fly. The lab was recently awarded a “Wellcome Trust Investigator Award” in order to fund this research.
It was once said that sequencing an organism’s DNA only gave us the characters of a play, the hard work is actually writing the story. We are only starting to glimpse at how complex life’s story really is.