Figure 5

Neighbor-joining phylogenetic tree of eukaryote Hog domain protein sequences. The Hh, Groundhog (Grd), Warthog (Wrt), Quahog (Qua), and new Lophohog families are indicated. Sequence names are color-coded according to phyletic divisions, except for sponges. Chromadorea and Enoplea are two major nematode divisions. Protist is loosely used to encompass all non-metazoans. The Hint domains of Vint proteins were used as outgroup and bootstrap values ≥ 40% are shown. Most of the sequences and the analysis methods are described in [10]. Additional sequences were added to this analysis from sponges [19], and BLAST searches were carried out at JGI [72] of the genomes of L. gigantea and Capitella I ECS-2004. From Capitella I ECS-2004 one hh and one hh-related gene were retrieved, and from L. gigantea one hh and six other Hog genes were retrieved. Capitella Cap_213608 and L. gigantea Lg_236513, which encodes an export signal peptide, form a clade, although not with high bootstrap significance. Interestingly, this clade clusters with the Cnidarian hh-related genes - although bootstrap values are insignificant. Five L. gigantea Hog genes (Lg_173620, Lg_173619, Lg_237232, Lg_FC606200, Lg_229767) form a distinct clade, but these genes are very divergent from the Hog domains of the other metazoan genes. These genes encode only a few residues upstream of the Hog domain (7-15), and lack an export signal peptide. This unusual structure is confirmed by multiple expressed sequence tags (ESTs) for each gene. Do these genes represent a highly divergent form of Hog-only proteins in this gastropod, or do they stem from another organism, perhaps some ciliated protozoan parasite found in L. gigantea [73]? More analysis will be necessary to resolve this.