Nature reports: Researchers want to understand how the cephalopods, a class of free-floating molluscs, produced a creature that is clever enough to navigate highly complex mazes and open jars filled with tasty crabs.

Surprisingly, the octopus genome turned out to be almost as large as a human’s and to contain a greater number of protein-coding genes — some 33,000, compared with fewer than 25,000 in Homo sapiens.

This excess results mostly from the expansion of a few specific gene families, [neurobiologist Clifton] Ragsdale says. One of the most remarkable gene groups is the protocadherins, which regulate the development of neurons and the short-range interactions between them. The octopus has 168 of these genes — more than twice as many as mammals. This resonates with the creature’s unusually large brain and the organ’s even-stranger anatomy. Of the octopus’s half a billion neurons — six times the number in a mouse — two-thirds spill out from its head through its arms, without the involvement of long-range fibres such as those in vertebrate spinal cords. The independent computing power of the arms, which can execute cognitive tasks even when dismembered, have made octopuses an object of study for neurobiologists such as Hochner and for roboticists who are collaborating on the development of soft, flexible robots.

A gene family that is involved in development, the zinc-finger transcription factors, is also highly expanded in octopuses. At around 1,800 genes, it is the second-largest gene family to be discovered in an animal, after the elephant’s 2,000 olfactory-receptor genes. [Continue reading…]