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Octopus Brain Complexity Linked to MicroRNA Expansions

In Science Advances, an international team led by investigators in Germany and the US describe cephalopod microRNAs that appear to contribute to cognitive features in the octopus species Octopus vulgaris and other coleoid, or soft-bodied, cephalopod species. Based on messenger RNA and small RNA sequences in 18 O. vulgaris tissues and in two other coleoid cephalopod species — the octopus O. bimaculoides and bobtail squid Euprymna scolopes — the team tracked down 43 gene families not found by sequencing a non-coleoid Nautilus species from a sister cephalopod group. A subset of nearly three dozen expanded miRNA families turned up in the Octopus species alone, the authors explain, noting that the miRNA set expansions tended to include miRNA families expressed during cephalopod development and in the animals' neuronal tissue types. "With respect to the development of the nervous system, we note that at least in vertebrates, miRNAs are known to have highly complex expression patterns with, for example, miRNA transcripts localized to the synapse and modulating their function," they suggest. "Although it remains to be seen whether these types of pathways operate in coleoids, the notable explosion of the miRNA gene repertoire in coleoid cephalopods may indicate that miRNAs and, perhaps, their specialized neuronal functions are deeply linked and possibly required for the emergence of complex brains in animals."