Characterization on the alternative splicing, expression and gene phylogenesis of PTPR4 family in Japanese flounder, Paralichthys olivaceus

One mechanism of eukaryotic signaling is protein phosphorylation by protein tyrosine phosphatases (PTPs). Here we have identified the PTP Receptor-Type IV (PTPR4) family, including one form of PTPα and two forms of PTPε (PTPε M and PTPε C) in flounder. The existence of PTPε C has not been reported in non-mammalian animals. Semi-quantitative RT-PCR revealed independent expression patterns and levels of PTPα and the two forms of PTPε in various tissues. The sequence of PTPε C was identical to that of PTPε M except for its 5’-terminal regions. Southern blot analysis proved that there existed only one PTPε gene in flounder genome, indicating that the two isoforms of PTPε might have been derived from alternative splicing of the single gene. Phylogenetic analysis of PTP domain D2 and part of D1 of PTPR4 showed that flounder was first joint with other teleost fish and then tetrapods, and also provided evidence that the gene duplication from the ancestor gene to PTPα and PTPε occurred before the divergence of Gnathastomata and Agnatha. These results showed that the functional evolution of protein phosphorylation is promoted by not only genome duplication, but also elaborate regulation of gene expression.