Novel and Conserved Features of the Hox Cluster of Entoprocta (Kamptozoa)

Hox genes are highly conserved developmental genes involved in the patterning of the anterior-posterior axis of nearly all metazoan animals. While Hox genes have been characterized for many bilaterians, several cryptic taxa, often comprising microscopic specimens, have hitherto been neglected. We here present the first combined transcriptomic and genomic Hox gene study for Entoprocta (=Kamptozoa), a phylum of microscopic, sessile, tentacle-bearing animals with unresolved phylogenetic affinities. We identified 10 of the 11 Hox genes commonly found in other lophotrochozoans. The analyses of transcriptomic data of different developmental stages of three species (regenerating stages of the colonial species Pedicellina cernua, budding stages of the solitary species Loxosomella vivipara and embryos of the solitary species Loxosomella murmanica/atkinsae) yielded the Hox genes Labial, Hox3, Lox5, and Post2 in all species. Pb and Dfd were only found being expressed in the colonial species P. cernua. Lox4 was uniquely expressed in the solitary species L. vivipara and L. murmanica/atkinsae. Other homeobox genes belonging to the ANTP-class genes, e.g., ParaHox and NK-like genes, were also found. Thus, in addition to newly identified Hox genes (PceLox2-like & LviPost2-like), Entoporocta show the typical lophotrochozoan Hox pattern besides the loss of the posterior class Hox gene Post1.