Home » Technology » the squid is able to modify its own genetic code

the squid is able to modify its own genetic code

The squid (or squid) is a fascinating animal, which never ceases to surprise marine biologists with its cognitive capacities. Researchers at the Marine Biology Laboratory in Woods Hole, Massachusetts, recently discovered that this cephalopod has another extraordinary ability: it is able to modify its own genetic code, not only in the nucleus of neuronal cells, but also in the nerve fibers that carry the signal. A first in the animal world.

The team of Joshua Rosenthal, neurobiologist at the origin of the study, has just published its results in the review Nucleid Acids Research. In 2015, these researchers had already highlighted that the squid had the power to edit its own messenger RNA instructions at an exceptional level (much more than what we observe in humans). As a result, this species has the ability to very precisely define the type of proteins that will be produced in its nervous system. No fewer than 57,000 recoding sites have been identified in the squid’s brain (compared to only 100 known recoding sites in humans), which implies enormous protein diversity.

At the time, experts believed that all changes to the RNA occurred in the nucleus, and that the resulting messenger RNA was exported to the cell. But their latest discovery changes the game: it appears that the squid can modify its RNA not only in the nucleus, but also at the periphery of the cell. An observation that completely upsets the foundations of molecular biology.

This discovery implies in particular that the animal is a priori capable of modifying the function of proteins “à la carte”, according to the needs of the cell. Which gives it exceptional adaptability.

Messenger RNA, key to protein synthesis

The genetic information of a cell is contained in its DNA and this information must be translated into proteins to be “exploitable”. This is where messenger RNA (mRNA) comes in: it’s a transient copy – with a limited lifespan – of a portion of DNA, which contains all the instructions for assembling a protein, in other words, its gene. It is expelled from the nucleus to inform the rest of the cell. This mRNA transcription and translation process is used by cells in the body to synthesize the proteins they need for their metabolism. However, these cellular needs vary according to various factors (environment, stage of development, age of the cell, etc.). The production of mRNA thus adapts to the conditions in which the cell is found. Whenever a protein is needed, the cell transcribes the corresponding mRNA.

mRNA synthesis scheme

Diagram of the mRNA synthesis process. Credits: Wikimedia Commons / Fdardel CC BY-SA

Once the mRNA leaves the nucleus, the message it carries – the genetic information encoding the protein – cannot a priori be changed. At least that’s what scientists have thought so far. The Rosenthal team’s discovery casts doubt on this theory: in nerve cells in squid, modification of mRNA data outside the nucleus is indeed possible. This massive change in the nervous system is simply unprecedented in the animal world.

On the same subject : The genes for the development of the eyes of cephalopods are the same as those forming our legs

A faculty that extends beyond the nucleus

To reach their conclusion, the researchers took nerves from specimens of adult male coastal squid (Doryteuthis pealeii), and then analyzed the expression of proteins in neurons. They then discovered that the mRNA was being edited outside the cell nucleus, more specifically in the axon (the nerve fiber that extends the neuron and transmits the electrical signal to synaptic areas).

anatomy squid neural diagramanatomy squid neural diagram

Above: diagram of the squid anatomy showing the location of the “giant axon”, an unusually large neural projection, which in part controls the squid’s propulsion system, used for movement, attack and very quick escapes. Below: diagram of a neuron, showing the location of the nucleus where any modification of RNA was thought to occur, and of the axon, where local modification of RNA was identified in squid. Credits: Vallecillo-Viejo et al, Nucl. Acids Res., 2020.

This phenomenon allows squid to regulate their protein production more finely, and in an ultra localized manner, as the authors of the publication explain: ” Such a process could refine the function of proteins to help meet the specific physiological demands of different cell regions ” The team also noted that the editing of mRNA at the axon of the nerve cell turns out to be much greater than inside the nucleus.

Towards a treatment of human neuropathies

This raises a new mystery: why do squid need so many changes to their mRNA? Rosenthal and his colleagues had already demonstrated in 2017 that octopus and cuttlefish also exploit mRNA editing to diversify the proteins they produce in their nervous system. This may explain why these cephalopods are so intelligent compared to other invertebrates. A previous study has indeed highlighted the amazing ability of cuttlefish to make decisions: researchers from the University of Cambridge have found thatthey were able to regulate their appetite by eating less during the day knowing that their favorite meal was planned for the evening! Evidence of particularly complex cognitive abilities.

If Rosenthal’s study is about squid, it could be a serious lead towards developing a treatment for neurological disorders in humans, which are caused by neuronal dysfunction. Some specialists are studying the possibility of exploiting the natural RNA editing process to correct these dysfunctions, a technique that appears less risky than the manipulations carried out directly at the DNA level. ” Editing RNA is much safer than editing DNA Says Rosenthal. ” If you make a mistake, the RNA turns around and goes ” In fact, in the event of an error, the transcription of the gene stops and the mRNA is gradually degraded.

Sources: Nucleic Acids Research, I. C. Vallecillo-Viejo and J. Rosenthal and Marine Biological Laboratory (MBL)

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.