Cloning and expression of Vitellogenin 2 gene from the intertidal copepod Tigriopus japonicus

Vitellogenin (Vg) is the precursor of the egg yolk protein vitellin. Vg induction has been used as a biomarker of exposure to endocrine disrupting chemicals in fish. However, in copepods limited information on the Vg gene is available only from two species, the salmon louse Lepeophtheirus salmonis and the intertidal copepod Tigriopus japonicus. By differential display of RNA expression between male and female adults, we identified another Vg member, i.e., vitellogenin 2 (Vg2) gene from T. japonicus. The full cDNA sequence was 5629 bp containing 5400 bp of an open reading frame. The expression of Vg transcripts was negligible in all naupliar stages and copepodid stages 1 to 4 but was detectable in female copepods of stage 5 and 6. Female adults expressed over 270 times more Vg transcripts than male adults.