Gene fishing: the use of a simple protocol to isolate multiple homeodomain classes from diverse invertebrate taxa.

Comparison of relevant gene sequence and functional data is central to understanding the evolution of metazoan development. The conservation of portions of regulatory genes, such as homeoboxes, allows for the design of PCR-based sequence isolation and amplification strategies. Here we describe a simple protocol that uses a degenerate primer pair to isolate a variety of homeobox-containing genes from diverse metazoan taxa. In a nonexhaustive survey, we have isolated 28 gene sequence fragments from 15 taxa, representing eight invertebrate phyla (Mollusca, Echiura, Annelida, Platyhelminth, Acoela, Ctenophora, Cnidaria, and Porifera). Based on BLAST and parsimony analyses, these gene fragments affiliate with several gene groups (PAIRED-like, HOX, and ParaHOX) and several single genes, including pancreas/duodenum homeoboxes (Pdx), empty spiracles (ems/Emx), gastrulation brain homeoboxes (Gbx), hematopoietically expressed homeoboxes (HEX), brain specific homeobox (bsh/BarH1/BarH2), NK-1 (NK-1/s59/slouch), and ladybird (Lbl/Lbe/Lbx). In several cases, these fragments represent the first reported orthologue for the phylum or superphyletic group (i.e., Lophotrochozoa).