Evolutionary history of the podoplanin gene

Podoplanin is a type I small mucin-like protein involved in cell motility. We have identified and studied the podoplanin coding sequence in 201 species of vertebrates, ranging from cartilaginous fishes to mammals. The N-terminal signal peptide is coded by the first exon; the transmembrane and intracellular domains are coded by the third exon (except for the last amino acid, coded in another exon with a long 3'-UTR). The extracellular domain has undergone variation during evolutionary time, having a single exon in cartilaginous fishes, teleosts, coelacanths and lungfishes. In amphibians, this single exon has been split in two, and in amniotes, another exon has been acquired, although it has been secondarily lost in Squamata. The podoplanin evolutionary tree agrees with the species tree in most cases. Two functional elements in the proteins, the GXXXG dimerization motif in the transmembrane domain and the region where podoplanin is cleaved by γ-secretase are subjected to positive selection.