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In more than one sense, humans and abalone may be distant cousins

By Elizabeth O'Brien - posted Tuesday, 12 August 2003

The question of our origin has fascinated mankind over the centuries. What makes us human, or a fly a fly? It has a lot to do with our DNA code. DNA or deoxyribonucleic acid carries the information required for the correct development and survival of an organism. The information in DNA is activated by specific coding regions, known as genes, resulting in production of enzymes or structural proteins or the regulation of the activity of other genes. When we analyse DNA code we find incredible genetic similarity between very different animals.

The development of animals in general involves a complicated network of gene activation at the right time and place in the body. However, some genes are so well suited to the roles they play, regions of their code and their utilisation in building equivalent organs in very different animals have remained unchanged despite millions of years of evolution.

The tropical abalone, Haliotis asinina, is a marine snail considered to be a seafood delicacy which, I'm sure we would all agree, has little resemblance to humans. It also differs greatly from the well-studied mouse, nematode and fruit fly making it an interesting organism for comparison at the gene level. By applying what we know about the conserved code in other animals such as mice, fruit flies and nematodes, we have been able to isolate comparable genes from the abalone


We targeted POU (pronounced pow) and Pax-type genes in the abalone as they have been found in the brains of mice, flies and nematodes. Of the three types of POU genes found in the other animals, two were present in the abalone brain and of the five Pax gene types, two were found in abalone brain. Comparing these genes revealed 89 to 99 per cent similarity between the conserved coding regions in mice and abalone. But are they doing the same thing?

We also looked at where these genes were active in the abalone and compared that other animals. When the abalone is a larvae, the POU genes are active in the functioning and developing brains. Unlike humans and mice, abalone have several brains (ganglia) that coordinate different regions of their body. The front brains (the anterior ganglia) are also responsible for producing growth and reproduction hormones in the adult. These adult ganglia have active Pax genes as well as POU genes. This is consistent with other animals where these genes are also expressed in the developing and adult central nervous system.

The abalone is also capable of sensing a wide range of stimuli including temperature, touch, light, taste, smell and gravity. During the development of specialised sense organs in the abalone we found the presence of active POU and Pax genes. These genes are also active in the comparative sense organs of mice, flies and nematodes. Particularly interesting is activity in the organ system that detects gravity.

Most animals can discern up from down and tend to use a comparable organ to do so. In general, this consists of a sphere of sensory cells that encircle a fluid filled cavity. Within the cavity are small pebble-like weights that can move freely in the fluid. When the animal moves down the weights shift to the bottom of the organ and activate the sensory cells, which is then interpreted by the brain or ganglia to indicate the animal's position.

In abalone this structure is known as the statocyst, in humans and other mammals it is the inner ear and all express POU and Pax genes. These genes are not only active in the balance organ of the abalone and mouse but also in jellyfish! This has amazing implications for human ancestry.

The common code and function of POU and Pax genes in animals as different as humans, abalone and jellyfish indicates that we share a common ancestor which was able to sense and interpret its environment.


Conservation of gene code and function in animals that have evolved independently for millions of years also indicates an essential function for these genes. They are so well suited to the role they play that they have not been altered for millennia. Not only is this important in reconstructing the animal ancestor but also for understanding the genes involved in the normal development of our own organ systems.

It's amazing to think about how powerful evolution can be. A common starting point gave rise to animals as complex and as different as abalone and humans. With each new discovery we move closer to understanding and appreciating our origin.

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About the Author

Dr Elizabeth O'Brien is a Fisheries Biologist with the Queensland Department of Primary Industries.

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