Identification of the Vo domain of V-ATPase in Bombyx mori silkworm.

Vacuolar H-ATPase (V-ATPase) is very important for eukaryotes and consists of a conserved V domain and slightly variable Vo domain. However, the Vo domain has not been systematically identified in the silkworm Bombyx mori. In this study, 11 Vo domain subunit members were identified throughout the genome of B. mori, including four isoforms of subunit a (BmVoa1-4), two isoforms of subunit e (BmVoe1-2), one each of subunit c″ (BmVob), subunit c (BmVoc), and subunit d (BmVod), and two accessory subunits (BmVoap1 and BmVoap2). Further analysis revealed BmVoa3 and BmVoa4 were located on the same chromosome and had similar molecular weights and isoelectric points, but separated to different small branches on the phylogenetic tree. Reverse transcription polymerase chain reaction results indicated that most Vo domain subunits were expressed during all silkworm developmental stages. Quantitative polymerase chain rection (qPCR) showed BmVoa1 was hemocyte-specific and BmVoe1 was testis-specific. BmVoa2 was not expressed in the midgut, while the other members were specifically or highly expressed in the midgut and Malpighian tubules. Further qPCR analysis indicated BmVoa4 in the midgut and BmVoa3 in BmE cells were significantly induced by B. mori nucleopolyhedrovirus (BmNPV), suggesting that these two genes may be involved in BmNPV infection.