K. Kuhn et al., Isolation of hox genes from the scyphozoan Cassiopeia xamachana: Implications for the early evolution of hox genes, J EXP ZOOL, 285(1), 1999, pp. 63-75
The isolation of Hox genes from two cnidarian groups, the Hydrozoa and Anth
ozoa, has sparked hypotheses on the early evolution of Hox genes and a cons
erved role for these genes for defining a main body axis in all metazoan an
imals. We have isolated the first five Hox genes, Scox-1 to Scox-5, from th
e third cnidarian class, the Scyphozoa. For all but one gene, we report ful
l-length homeobox plus flanking sequences. Four of the five genes show clos
e relationship to previously reported Cnox-1 genes from Hydrozoa and Anthoz
oa. One gene, Scox-2, is an unambiguous homologue of Cnox-2 genes known fro
m Hydrozoa, Anthozoa, and also Placozoa. Based on sequence similarity and p
hylogenetic analyses of the homeobox and homeodomain sequences of known Hox
genes from cnidarians, we suggest the presence of at least five distinct H
ox gene families in this phylum, and conclude that the last common ancestor
of the Recent cnidarian classes likely possessed a set of Hox genes repres
enting three different families, the Cnox-1, Cnox-2, and Cnox-5 families. T
he data presented are consistent with the idea that multiple duplication ev
ents of genes have occurred within one family at the expense of conservatio
n of the original set of genes, which represent the three ancestral Hox gen
e families. (C) 1999 Wiley-Liss, Inc.