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 PTPalpha and two forms of PTPepsilon (PTPepsilon M and PTPepsilon C) in flounder. The existence of PTPepsilon C has not been reported in non-mammalian animals. Semi-quantitative RT-PCR revealed independent expression patterns and levels of PTPalpha and the two forms of PTPepsilon in various tissues. The sequence of PTPepsilon C was identical to that of PTPepsilon M except for its 5'-terminal regions. Southern blot analysis proved that there existed only one PTPepsilon gene in flounder genome, indicating that the two isoforms of PTPepsilon 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 PTPalpha and PTPepsilon 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.