Researchers have found that Cnidaria, a group of marine animals noted for diverse morphology among its constituent species, actually lacks the ancient "Hox" gene system that is essential for the development of most other animals. The finding is surprising because the Hox system is largely responsible for so-called axial patterning, the developmental process that directs the formation of different morphological features along the anterior-posterior axis--the axis along which the head, trunk, and tail are arranged. The work indicates that despite the importance of the Hox system in the development of most animals, the evolution of a typical Hox system is not in fact a prerequisite for axial patterning during development or for the generation of diverse animal morphology.

The findings are reported in the May 9th issue of Current Biology by scientists Bernd Schierwater, Kai Kamm, and Wolfgang Jakob of Tierrztliche Hochschule Hannover, in Germany, Stephen Dellaporta of Yale University, and David Miller of James Cook University in Australia.

A remarkable feature of Hox-system genes is that they are typically clustered in groups along chromosomes, with their order along the chromosome reflecting their actual pattern of expression along the anterior-posterior axis of a developing animal. The Hox system has long been considered a defining characteristic of animals, and much of the variation seen in animal morphology has been attributed to evolutionary variations on how the Hox system is implemented during development in different species.

In the new work, the researchers investigated the Hox status of cnidarians--a group of primitive animals that diverged very early on in animal evolution from the lineage leading to most other animal species. Cnidarians include reef-building polyps and pelagic jellyfish, while the group from which it split--the Bilateria--has given rise to the vast majority of the animals we are familiar with, including worms, fish,
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Contact: Heidi Hardman
hhardman@cell.com
617-397-2879
Cell Press
4-May-2006

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