Natures wonders: the brilliant octopus (Introduction)

by David Turell @, Thursday, August 27, 2015, 01:06 (1456 days ago) @ David Turell

They have half a billion neurons, many in each leg, a big brain, camera eyes and a strangely evolved DNA with 33,000 genes:

"While the octopus genome resembles those of other marine invertebrates in many respects, it also revealed unexpected features that are key to understanding the origin and function of its unique nervous system. Cephalopod brains are elaborations of the basic invertebrate brain, and have a completely different organization than what is found in humans and other vertebrates. Cephalopods emerged as predators in the ancient oceans over three hundred million years ago. “They were the first intelligent beings on the planet,” quipped Nobel Laureate Dr. Sydney Brenner, founding President and Distinguished Professor of OIST. Prof. Brenner was fascinated with the great sophistication of their nervous system and initiated the octopus Genome Project as the first of several important genome projects that have become a hallmark of OIST. The complexity of the octopus genome presented a major challenge.

"The octopus genome encodes several large gene families that may hold the key to how the animal wires up its complex brain - these gene families are involved in regulation brain development in other animals, but they are vastly expanded in octopus. Their detailed role, however, remains unknown. Hundreds of other genes that are common in cephalopods but unknown in other animals were also found. Some of these are implicated in the dynamic skin of cephalopods that enables spectacular camouflage. Some of the team's findings raise questions about our understanding of genomic reorganization through evolution.

"Besides recognizable genes, vast swathes of the genome consist of regulatory networks that control how genes are expressed in cells. In the octopus, nearly half of the genome was found to be composed of mobile elements called transposons, one of the highest proportions in the animal kingdom. Transposons replicate and move around with a life of their own, disrupting or enhancing gene expression and facilitating reshufflings of gene order. The researchers found many of them to be particularly active in the octopus nervous system.

"Genes that are grouped together on chromosomes in other animals were dispersed in the octopus genome, likely as a result of transposon activity. The “Hox” genes, involved in embryonic development in all animals, are a particularly dramatic example. Although clustered together in most animals, including other mollusks, they are scattered in snippets in the octopus, presumably enabling the evolution of the versatile cephalopod body plan.


"As humans, we like to think we are unique in evolutionary terms, but the octopus could reveal that this is not the case. One reason the octopus fascinates scientists is that its brain became organized to be able to carry out such incredible, complex tasks without adopting the principles of the vertebrate brain. Further examination will tell if the building blocks of its nervous system are as radically different from those of vertebrate landlubbers like us, as the octopus's abilities suggest.'

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