Osmia cornifrons vitellogenin: cDNA cloning, structural analysis and developmental expression

Osmia cornifrons plays a major role in the pollination of orchards, but basic information on vitellogenin and oocyte development is limited. To better understand vitellogenin in hymenopteran insects, we cloned a cDNA encoding vitellogenin from the hornfaced bee O.cornifrons. Osmia cornifrons vitellogenin cDNA contains 5477bp with an open reading frame of 1783 amino acid residues, and has a predicted molecular mass of approximately 200.21kDa and a pI of 6.55. Osmia cornifrons vitellogenin possesses four consensus (RXXR/S) cleavage sites and has conserved DGXR and GL/ICG motifs in the C-terminus. The deduced amino acid sequence of the O.cornifrons vitellogenin cDNA showed a 66% identity with Megachile rotundata, 53% to Apis mellifera, 51% to Bombus ignitus and 42%-30% with other hymenopteran insect vitellogenins. Phylogenetic analysis showed that O.cornifrons vitellogenin clustered with vitellogenins from Megachilidae, Apidae, Vespidae and Formicidae species but not with those from Pteromalidae, Aphelinidae or Ichneumonidae species. The expression profile of O.cornifrons vitellogenin mRNA during development revealed that O.cornifrons vitellogenin was first detected in the pupal stage and was continuously detected during the adult stage. Interestingly, O.cornifrons vitellogenin mRNA expression was low in mid-diapause, then gradually increased beginning on day3 of the newly emerged adult stage, and subsequently declined. These results suggest that the expression level of O.cornifrons vitellogenin mRNA is stage-specific.