Genome of ancient sponge reveals origins of first animals, cancer

The sponge, which was not recognized as an animal until the 19th century, is now the simplest and most ancient group of animals to have their genome sequenced.

In a paper appearing in the August 5 issue of the journal Nature, a team of researchers led by Daniel Rokhsar of the University of California, Berkeley, and the Department of Energy's Joint Genome Institute (JGI), report the draft genome sequence of the sea sponge Amphimedon queenslandica and several insights the genome gives into the origins of both the first animals and cancer.

All living animals are descended from the common ancestor of sponges and humans, which lived more than 600 million years ago. A sponge-like creature may have been the first organism with more than one cell type and the ability to develop from a fertilized egg produced by the merger of sperm and egg cells – that is, an animal.

"Our hypothesis is that multicellularity and cancer are two sides of the same coin," said Rokhsar, program head for computational genomics at JGI and a professor of molecular and cell biology and of physics at UC Berkeley. "If you are a cell in a multicellular organism, you have to cooperate with other cells in your body, making sure that you divide when you are supposed to as part of the team. The genes that regulate this cooperation are also the ones whose disruption can cause cells to behave selfishly and grow in uncontrolled ways to the detriment of the organism."

As part of the new analysis, the team looked in the sponge genome for more than 100 genes that have been implicated in human cancers and found about 90 percent of them. Future research will show what roles these genes play in endowing sponge cells with team spirit.

Sponges are often described as the "simplest" living animals, while humans are considered relatively "complex," but how this differential complexity is encoded in the genome is still a major question in biology The new study shows that, while the sponge genome contains most of the gene families found in humans, the number of genes in each family has changed significantly over the past 600 million years. By analyzing which gene families were enriched or depleted in different groups of animals, the authors identified groups of gene functions that are associated with morphological complexity.

"The genome raises questions of what it means to be an animal," said first author Mansi Srivastava, a former UC Berkeley graduate student who now is a post-doctoral associate at the Whitehead Institute for Biomedical Research in Cambridge, Mass. …

"This incredibly old ancestor possessed the same core building blocks for multicellular form and function that still sits at the heart of all living animals, including humans," said coauthor Bernie Degnan, a professor of biology at the University of Queensland, Australia, who collected the sponge whose genome was sequenced from the Great Barrier Reef. "It now appears that the evolution of these genes not only allowed the first animals to colonize the ancient oceans, but underpinned the evolution of the full biodiversity of animals we see today." …

Genome of ancient sponge reveals origins of first animals, cancer

Technorati Tags: genetic engineering