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Hox genes in bilaterians specify distinct regions along the anterior-posterior axis. A question of interest is when in metazoan evolution did this class of genes take on this function. Hox genes have been isolated from a number of cnidarian species including hydra. The expression patterns of two of them, Cnox-3 and Cnox-2 have been examined in adult hydra. Cnox-3, a labial homologue, plays a role in oral/anterior patterning, while Cnox-2, a Deformed homologue or a Gsx homologue of the ParaHox cluster appears to repress anterior patterning in the body column. The two genes play a role in axial patterning that is consistent with the tissue dynamics of an adult hydra.
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Hans Robert Bode (2001) studied this question.
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