Octopuses’ Genetic Secret: RNA Editing
Written by Megan Farrow, Illustration by Angela Zhu
The central dogma of biology deems that information flows from DNA to RNA to proteins, any change in DNA or RNA, whether good or bad, has the potential to change what proteins are produced. Storing all of our genetic information, DNA behaves as a template for the majority of traits expressed by an organism! This being the case, all organisms would want to follow DNA as closely as possible… Right??
Surprisingly, it has been discovered that many organisms do actually undergo RNA editing! In fact, even we humans edit a ton of RNA in our brains though it often does not lead to a change in amino acids. Cephalopods, such as octopuses and squids, however, have been found to edit RNA at very high rates with greater than normal changes in protein sequences!
When it comes to their nervous systems, RNA editing runs particularly rampant. In Longfin Squids, 70 percent of edits in protein-producing RNAs recode the proteins! Moreover, RNA in the nervous systems of cephalopods is often re-coded three to six times as often as in other organs or tissues.
Some RNA may have multiple edit sites which can result in many different versions of a protein being coded, suggests Kavita Rangan, a molecular biologist at the University of California. Rangan believes that having a wide selection of proteins may give cephalopods more flexibility in responding to the environment. Having extra RNA editing in the nervous system may be what contributes to their flexibility in thinking, giving octopuses the ability to unlock cages or use tools!
These RNA edits don’t provide evolutionary advantage, holding DNA evolution back, and these re-coding ‘nonsynonymous’ sites are harmful so why do cephalopods keep at it? An evolutionary geneticist from the University of Michigan in Ann Arbor, Jianzhi Zhang, suggests that RNA editing may not be about gaining anything but rather that it may be addictive. These RNA edits may permit harmful changes to DNA by allowing the continued production of correct proteins, keeping the organism healthy. For example, if DNA gets mutated, the mutation may lead to a harmful amino acid change in a protein; the genetic change would be weeded out by natural selection. However, if the organism has RNA editing, the mistake in the DNA can be corrected before translation to proteins. If this occurs with an essential protein, RNA would have to be edited at high levels, forcing the cephalopod to stay trapped in the cycle. Without genetic mutations being weeded out by natural selection, it is passed down from generation to generation.
There are still many questions that remain and future experiments that need to be run. Rangan would like to be able to grow squid cells to get a true sense of the ongoing processes. Currently, the best she can do is take tissue directly from the squid which only gives her snapshots of what is happening. Zhang would also like to further test his theories by getting yeast cells ‘addicted’ to RNA editing.
Source
https://www.sciencenews.org/article/octopus-squid-rna-editing-dna-cephalopods