Conservation and Phylogeny of a Novel Family of Non-Hox Genes of the Antp Class in Demospongiae (Porifera)

Abstract

A survey across the most basal animal phylum, the Porifera, for the presence of homeobox-containing genes led to the isolation of 24 partial or complete homeobox sequences from 21 sponge species distributed in 15 families and 6 orders of Demospongiae. All the new sequences shared a high identity/similarity with EmH-3 (Ephydatia muelleri), a non-Hox gene from the Antp class. The Demox sequences, EmH-3, and related homeodomains formed a well-supported clade with no true affinity with any known bilaterian family, including the Tlx/Hox11 family, suggesting that the EmH-3 family of genes, comprising 31 members, represents a novel family of non-Hox genes, called the Demox family, widespread among Demospongiae. The presence of the Tlx/Hox11 specific signature in the Demox family and common regulatory elements suggested that the Demox and Tlx/Hox11 families are closely related. In the phylogenetic analyses, freshwater Haplosclerida appeared as monophyletic, and Haplosclerida and Halichondrida as polyphyletic, with a clade comprising Agelas species and Axinella corrugata. As for their expression, high levels of Demox transcripts were found in adult tissues. Our data add to the number of published poriferan homeobox sequences and provide independent confirmation of the current Demospongiae phylogenies.

Six major steps in animal evolution: are we derived sponge larvae?

“…They are multicellular but have only a comparatively low number of cell types, and epithelia with occluding cell junctions and Hox genes are not found (Tyler 2003;Richelle-Maurer et al 2006). All sponges have ciliated, lecithotrophic larvae, and sessile adults with choanocytes situated in internal chambers.…”

The Homoscleromorph sponge Oscarellalobularis, a promising sponge model in evolutionary and developmental biology

“…11, 14–16 Nevertheless, phylogenies based on different molecular datasets testing the relationships between these sponge lineages on one hand and their relation to non‐sponge (eumetazoan) taxa (Ctenophora, Placozoa, Cnidaria and Bilateria) on the other hand, have provided conflicting results7, 10–12, 15, 17–21 and thus do not permit an unambiguous resolution for these questions. However, sponges still remain, as basal lineages, key organisms for unraveling early metazoan evolution, as illustrated by the growing interest for sponges (and more largely for ‘non‐bilaterian’ animals) in the evolutionary and developmental (Evo–devo) field over the last 5 years 22–31…”

Protein evolution of ANTP and PRD homeobox genes

“…Furthermore, the ANTP Demox class found in Demospongiae and apparently absent in all other animals [19], is characterized by the presence of the ANTP-PRD, and ANTP 1 and 2 patterns, as expected for ANTP genes that do not belong to the HOXL or NKL lineage (Table 3). Although there are no true Hox genes in sponges [20], 13 sequences show the full HOXL signature.…”