POU-domain sequences from the flatworm Dugesia tigrina.

Redundant primers matching well-conserved sequences within vertebrate and invertebrate POU genes were used in the PRC (polymerase chain reaction) to detect three different POU-domain-containing genes within the genome of the flatworm, Dugesia tigrina. Two of these genes appear to be close homologues of class-III POU genes previously identified in Dugesia japonica, while the third represents a new class-III POU gene. Nucleotide sequences encoding highly related POU domains within the two species of planaria exhibited a surprisingly poor degree of shared identity. Since only class-III POU genes have been observed to date in flatworms, these genes may represent ancestral versions of the multiple classes of POU genes that exist in vertebrates, and may play important roles in the development of metazoan nervous tissue.