The sequence and expression pattern of the Calliphora erythrocephala yolk protein A and B genes

The yolk protein genes (yps) are expressed in a temporal, tissue- and sex-specific fashion in Drosophila melanogaster. Here we report the sequence of two related genes in Calliphora erythrocephala. The predicted Calliphora yolk protein (YP) sequences are well conserved, especially at the C-terminal end when compared to those of D. melanogaster and Ceratitis capitata. Database searches with the Calliphora yolk protein B (CeYPB) sequence identify the vertebrate lipase similarity reported for the YPs of Drosophila and Ceratitis. Moreover, sequences with identity to divalent ion-binding sites were observed, which colocalized with putative tyrosine sulfation sites. Calliphora oogenesis differs from Drosophila in that it is cyclic in response to a meat feed. The Calliphora yp genes are expressed in the follicle cells of the egg chamber during vitellogenesis, as shown by in situ hybridization, and the yp message levels correlate with YP synthesis. The synthesis of the yp transcripts in ovaries of Calliphora occurs in the same pattern as that for ovarian transcripts in Drosophila. In the carcass, yp transcript levels are correlated with the production of a batch of eggs.