Cloning and expression study of the lobster (Homarus americanus) vitellogenin: Conservation in gene structure among decapods

This study reports the molecular characterization of the vitellogenin (Vg) of the lobster, Homarus americanus. Based on the annual collection of female lobsters, vitellogenesis commences in early March and continues through to September of each year. Using an antibody to vitellin of the lobster, H. americanus, several immunoreactive ovarian proteins were initially identified by Western blot analysis. The 80kDa protein contained the amino acid sequence APWGGNTPRC, identified subsequently by cDNA cloning to be identical to the lobster Vg. In common with the shrimp Metapenaeus ensis and crab Charybdis feriatus, the lobster HaVg1 gene comprises 14 introns and 15 exons. The deduced HaVg1 precursor is most similar to the Vg of the crayfish Cherax quadricarinatus (57%), followed by M. ensis (40-43% identity) and C. feriatus (38%). The results from genomic and RT-PCR cloning also confirmed the presence of multiple Vg genes in lobster. At early reproductive stages, the hepatopancreas HaVg1 transcript levels are low but increased to a maximum in animals with mature oocytes. The ovary, however, also expressed low levels of HaVg1. Using in vitro explant culture, treatment of hepatopancreas fragments with farnesoic acid or 20-hydroxyecdysone resulted in a significant stimulation in HaVg1 expression. From this study, it appears that Vg gene organization and expression pattern in decapods is highly conserved. Similar endocrine mechanisms may govern the process of vitellogenesis across the decapods.