Aspects of vegetative reproduction and developmental genetics in Diplosoma listerianum (Tunicata, Aplousobranchiata)
Hox and ParaHox genes are groups of key developmental transcription factors that are highly conserved throughout the Metazoa. Their order of expression along the body axis of an animal is not only highly conserved between different organisms, but is also collinear to the arrangement of individual genes along the chromosome. Studies of these developmental control genes can give valuable insights into the evolution of body plans. A total of 7 homeobox containing genes (dpl1-dpl7) were isolated form the D. listerianum genome. Four of these were members of the Hox gene family and of the ParaHox gene family. Initial fragments were isolated using the method of degenerate PCR with primers designed from the highly conserved amino acid sequence of the 1st and 3rd helix of the homeodomain. Short fragments limit gene characterisation and as such, regions flanking the degenerate PCR products were isolated, using inverse PCR, 3' and 5' RACE PCR. Phylogenetic relationships of the genes are also examined. Dpl1 exhibited high identities with the arthropod Antennapedia and the vertebrate Hox6 and Hox 7 paralogue groups. Phylogenetic analysis showed dpl1 to be more closely related to the Hox6 than to the Hox7 group genes. Dpl2 shares high identity with members of the Hox5/Scr paralogous group. Dpl3 has a high level of homology to the C. intestinalis gene CiIPF1. The Dpl3 homeodomain shared high identity with the ascidian H. roretzi and H. curvata cdx genes (Hr-cad and Hec-cdx, respectively), however differences in the hexapeptide regions, indicated high divergence of these genes in the ascidians. Dpl5 possessed features characteristic of posterior Hox genes and was most closely related to the C. intestinalis CiHbox5 gene. Dpl6 shared features common to the Hox 4 paralogous group Gsx ParaHox groups.