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MicroRNAs: Associated to the Evolution of Complex Octopus Brain

Octopus, soft-bodied cephalopod, is considered a remarkably intelligent invertebrate. It possesses an intricate network of nerves that makes it unique among lower organisms. It has an elaborated nervous system in terms of both magnitude and nature. Octopuses are capable of compiling and constructing shelters from discarded shells of coconut. They use water stream to capture various objects. A significant rise in RNA editing in the nervous system, may be responsible for the empirical success of this organism. This type of intelligence emerges in them due to the presence of microRNAs (miRNAs).

miRNAs are exceptionally conserved sequences that are involved in the expression of genes. These are considered as ‘dark matter’ of the animal genome because they do not synthesize any protein, however regulate the expression of the same. These are transcribed with the help of enzymes, RNA polymerase II and III. They produce a precursor which undergo an array of cleavages to form mature miRNA. These miRNAs work as the switch of lights that can regulate the expression of proteins in a cell.

Most of the RNA innovation in octopuses is an extension of miRNA gene reserve. These novel miRNAs are first expressed in the mature neural tissues. During the course of evolution, they got conserved. miRNAs show a complex pattern of inheritance for e.g., they are abundantly present in the synapses and modify their functions. Such miRNA expansions are comparable to that of vertebrates.

During a study Professor Peterson, Dr. Fromm et. al., analyzed miRNA data of three species of cephalopods; Octopus vulgaris, Octopus bimaculoides and Euprymna scolopes. They observed a significant increase in the miRNA of Octopus vulgaris and Octopus bimaculoides. It was an important finding as earlier it was observed only in humans, mammals and other higher vertebrates. They concluded that miRNAs are essential for the evolution of complex and exceptional brain

miRNAs perform specialized neuronal functions and are linked with the emergence of complexity in brains of vertebrates and octopuses.

Thus, it can be concluded that miRNAs are closely associated with evolution of complex brains in animals.

Dr. Anamika Tripathi

Schiller Institute Senior Secondary School

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