Molecular Characterization And Expression Analysis Of Vitellogenin In The Marine Crab Portunus Trituberculatus

As a precursor of the major yolk protein vitellin (Vn), vitellogenin (VG) has been studied in the crustacean for decades, mainly on shrimps. Little is known of the nature of VG molecule in crabs. The present research reports one cDNA encoding VG in the marine crab Portunus trituberculatus, an important commercial species in aquaculture. The cDNA sequence was 7846bp in length, which contained a 7680bp open reading frame encoding 2560 amino acid residues. The deduced amino acid sequence showed 32%-75% identities with other known crustacean VGs. Eleven potential cleavage sites (R-X-K/R-R/K) were identified from the deduced vitellogenin precursor. Cleaving of the precursor in these sites would result in the production of three major proteins (102kD, 100kD and 85kD) and several other small peptides, as shown by SDS-PAGE and Western blotting analysis. Northern blotting analysis revealed that the VG is mainly expressed in hepatopancreas. Its expression level is undetectable in the immature and premature crabs and varies during the mature stages. While by reverse transcription-polymerase chain reaction analysis the VG transcript was also identified in the ovary of the Portunus trituberculatus.