Genetic variations in the vitellogenin of Japanese populations of the wild silkworm Bombyx mandarina

We cloned and sequenced cDNA of Bombyx mandarina vitellogenin (BmaVg) inhabiting Japan. The complete sequence of BmaVg cDNA without a poly A tall is 5733 bp long and encodes 1780 amino acid residues among which are typical highly conserved sequences and common features found in most insects. Multiple alignment of vitellogenin sequences of Japanese Bombyx mandarina, the Chinese one, and Bombyx mori showed that the nucleotide sequence of Japanese BmaVg cDNA shared 99.5% identity with Chinese BmaVg and 98.2% identity with Bombyx mori vitellogenin (BmoVg), and that the amino acid sequence of Japanese BmaVg cDNA shared 99.6% homology with Chinese BmaVg and 97.5% homology with BmoVg. These findings indicate that BmaVg (JPN) is more similar to BmaVg (CHN) than to BmoVg, which was also confirmed through a comparison of the mutation frequencies of both nucleotide and amino acid sequences. The phylogenetic tree of Vgs demonstrates that BmaVgs of individuals collected from eighteen prefectures in Japan primarily cluster in a group with BmaVg (CHN) and without BmoVg, suggesting that the sequence variation between the two BmaVgs arose after divergence of B. mori from B. mandarina.