title: Homeobox gene diversification in the calcareous sponge, Sycon raphanus.
abstract: Knowledge of the developmental mechanisms in living basal metazoan phyla is crucial for understanding the genetic bases of morphological evolution in early animal history. We looked for homeobox genes in the calcareous sponge, Sycon raphanus, using the polymerase chain reaction. Partial sequences of eight homeoboxes were recovered, five of which are assignable to the NK-2 class of homeoboxes. The three remaining sequences are related members of a new class of homeoboxes, the Sycox class, showing limited similarity to bilaterian Lbx, Hlx, HEX, En, and Cad classes. Among the five NK-2 class homeoboxes are four closely related sequences occupying a divergent position within the class, the remaining one on the contrary showing high sequence similarity with members of the NK-2 family, a particular subgroup within the NK-2 class, previously known only from the Bilateria. This suggests that diversification of the NK-2 class occurred early in metazoan history. Altogether, the results reveal an unexpected diversification of homeobox genes in S. raphanus.
authors.affiliation: Laboratoire Diversité et Fonctionnement des Ecosystèmes Marins Côtiers (DIMAR CNRS UMR-6540), Centre d'Océanologie de Marseille, Université de la Méditerranée, Station Marine d'Endoume, Marseille, 13007, France. manuel@com.univ-mrs.fr
authors.forename: M
authors.initials: M
authors.lastname: Manuel
authors.forename: Y
authors.initials: Y
authors.lastname: Le Parco
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D015723:Gene Library; D005801:Genes, Homeobox / Q000235:genetics*; D014644:Genetic Variation; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D011161:Porifera / Q000145:classification* / Q000235:genetics*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
chemical_list: D018076:DNA, Complementary