Study identifies the crucial activity of transposable elements in the evolution of the octopus genomes

The octopus is an extraordinary organism with exceptional brain complexity and cognitive abilities that are unmatched by other invertebrates. So much so that it resembles vertebrates in certain ways more than it does invertebrates.

Study identifies the crucial activity of transposable elements in the evolution of the octopus genomes

Image Credit: Morten Brekkevold.

According to a study published recently in BMC Biology and coordinated by Remo Sanges from SISSA in Trieste and Graziano Fiorito from Stazione Zoologica Anton Dohrn in Naples, the neural and cognitive complexity of these animals may have its roots in a molecular analogy with the human brain.

The study demonstrates that the same “jumping genes” are active in the brains of two different species, the common octopus Octopus vulgaris, and the Californian octopus Octopus bimaculoides, a finding that might shed light on the mystery of these intriguing organisms’ intelligence.

Molecular copy-and-paste or cut-and-paste mechanisms allow transposons, also known as “jumping genes,” to “move” from one point to another of a person’s genome, shuffling or duplicating. This information was first obtained from the sequencing of the human genome in 2001. Most of the time, these moving parts are silent because they no longer move and have no visible effects.

Some have become dormant as a result of generations’ worth of mutations, while others are unaltered but obstructed by cellular defense mechanisms. Even these broken copies of transposons and their fragments can still be helpful from an evolutionary standpoint because they are considered to be “raw matter” that evolution can shape.

The most significant of these mobile elements are those from the so-called LINE (Long Interspersed Nuclear Elements) family, which are present in the human genome in 100 copies and may still be active.

Although it has long been believed that the activity of LINEs is only a relic of the past, a by-product of the evolutionary processes that involved these mobile elements, recent research has revealed that LINE activity is tightly controlled in the brain.

Many researchers believe that LINE transposons are connected to cognitive functions like learning and memory because they are particularly active in the hippocampus, which is crucial for the neural control of learning processes in human brains.

The octopus’ genome, like the human genome, is filled with “jumping genes,” most of which are dormant. The researchers found a member of the LINE family in regions of the brain essential for these animals’ cognitive abilities by concentrating on the transposons still capable of copy-and-paste.

The discovery was made possible by next-generation sequencing techniques, which were used to examine the molecular makeup of the genes active in the octopus nervous system. It was the result of a collaboration between Scuola Internazionale Superiore di Studi Avanzati, Stazione Zoologica Anton Dohrn, and Istituto Italiano di Tecnologia.

The discovery of an element of the LINE family, active in the brain of the two octopuses species, is very significant because it adds support to the idea that these elements have a specific function that goes beyond copy-and-paste.”

Remo Sanges, Director, Computational Genomics Laboratory, Scuola Internazionale Superiore di Studi Avanzati

Remo Sanges started working on this project while he was a researcher at Stazione Zoologica Anton Dohrn of Naples. The research was carried out by an international team with more than 20 researchers from all over the world. The study was published in the journal BMC Biology.

I literally jumped on the chair when, under the microscope, I saw a very strong signal of activity of this element in the vertical lobe, the structure of the brain which in the octopus is the seat of learning and cognitive abilities, just like the hippocampus in humans.

Giovanna Ponte, Stazione Zoologica Anton Dohrn

This similarity between man and octopus that shows the activity of a LINE element in the seat of cognitive abilities could be explained as a fascinating example of convergent evolution, a phenomenon for which, in two genetically distant species, the same molecular process develops independently, in response to similar needs,” adds Giuseppe Petrosino from Stazione Zoologica Anton Dohrn and Stefano Gustincich from Istituto Italiano di Tecnologia.

The brain of the octopus is functionally analogous in many of its characteristics to that of mammals. For this reason, also, the identified LINE element represents a very interesting candidate to study to improve our knowledge on the evolution of intelligence.”

Graziano Fiorito, Director, Department of Biology and Evolution of Marine Organisms, Stazione Zoologica Anton Dohrn

Source:
Journal reference:

Petrosino, G., et al. (2022) Identification of LINE retrotransposons and long non-coding RNAs expressed in the octopus brain. BMC Biology. doi.org/10.1186/s12915-022-01303-5.

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