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Three different studies regarding how pigmentation in different species of butterflies and moths are dependent on whether a particular gene is present or absent is changing the way molecular biologists view the standard explanation of how an organism’s genome is expressed.
Since the discovery of the structure of DNA, molecular biologists have worked hard to determine how the genetic information coded in an organism’s DNA manifests itself in the the structure and function of the organism itself. If you take a biochemistry class, you will learn the distilled understanding that has been shaped in that interval. The steps are as follows:
1. A signal is sent to a cell’s nucleus (where the DNA resides) that a particular protein is needed.
2. DNA exists as a double helix of two different long strands of the molecule, held together by hydrogen bonding between their base pairs. Following the signal, enzymes find the portion of a strand of DNA that codes for the desired protein, uncoil the DNA, and separates that strand from its complement strand.
2. Other enzymes read the sequence of base pairs and, in a process called transcription, produce a strand of RNA which contains the complementary code in the DNA for the protein. This RNA molecule is called “messenger” RNA (or mRNA, y’know, the stuff in the COVID vaccine).
3. The mRNA gets sent outside the nucleus to the cell’s protein factory, the ribosomes. In a process called translation, the ribosomes read the mRNA strand and produce the protein it codes for. Usually, these proteins themselves are enzymes which perform specific jobs within the organism.
4. The product protein is then sent to the portion of the cell (or some other place) where it is needed.
In shorthand, we can think DNA → mRNA → protein, and the protein performs the job deemed necessary by the original chemical signal to make it in the first place. This is how most of the work within an organism gets done. However, it’s not the only way. In the 1980s, it was discovered that some strands of RNA by themselves could also act as enzymes. Enzymatically active RNA molecules are called ribozymes, and the fact that they exist suggests that, evolutionarily, they pre-dated proteins as the molecules that did all the work in the organisms that existed when life first started.
Now, new studies (summarized in this article) on the genes that control pigmentation of butterflies and moths show that the crucial gene (which is the same in all species studied) does not code for a protein.
The discovery, detailed in three preprints this month, also represents the first time long noncoding RNA (lncRNA), so-called because it does not code for proteins, has been linked to the evolution of a visible trait in animals. “Now we have to pay more attention to noncoding RNA,” says Ilik Saccheri, an evolutionary biologist at the University of Liverpool….
The species studied were Heliconius erato (pictured above, as half normal coloring on the left, and with the gene coding for the lncRNA deleted on the right), the buckeye butterfly (Junonia coenia), and the squinting bush brown butterfly of Singapore (Bicycles anynana). The pigmentation of all of these species lightened to some degree when the gene coding for the relevant lncRNA was deleted from the butterflies’ DNA. Therefore, it most somehow be the lncRNA that is controlling the butterflies’ pigmentation, not a protein. The specific mechanism by which this control operates is still not understood, but it’s a clear objective for further work. Still more importantly, this is probably not the only instance of an lncRNA controlling the development or life processes of organisms. These RNA strands that have thus far been ignored are clearly capable of playing important roles throughout the biosphere, including ourselves. It will be exciting to see what those other roles turn out to be.
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