Cloning, expression and localization of the Daphnia carinata transformer gene DcarTra during different reproductive stages.

In this study, the full-length cDNA of the Transformer (Tra) gene from the common freshwater species Daphnia carinata (DcarTra; GenBank accession no. KJ735445) was cloned using primers based on homologous sequences and rapid amplification of cDNA ends (RACE). The relative expression and localization of DcarTra and the cellular abundance of the DcarTra protein during different sexual phases were subsequently investigated. The full-length DcarTra cDNA was 1620 bp with an ORF of 1143 bp encoding a 380 amino acid polypeptide. Phylogenetic analysis identified closely related genes in Daphnia magna and Daphnia pulex, and more distantly related genes in other insects. Quantitative PCR showed that DcarTra expression was highest in males, followed by sexual females, and lowest in parthenogenetic females. Whole-mount in situ hybridization showed that DcarTra was mainly expressed in the thoracic limbs, ovaries and rectum in parthenogenetic females, and in the joints of second antennae, ovaries, rectum and ventral processes in sexual females. Western blotting showed two differently phosphorylated forms of the Tra protein. When Tra is phosphorylated, DcarTra protein levels were much higher in males than in two females. Otherwise, when Tra is dephosphorylated, the highest Tra protein levels were in sexual females, which revealed that D. carinata can control the sexual transition via these two forms. Together these results suggest that DcarTra plays significant roles in the reproductive transformation of D. carinata and dephosphorylation of DcarTra may be the trigger for females to transform into males.