Genes with specific functions in the ovarian follicles of Calliphora erythrocephala (Diptera)

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.

A second maternally expressed Drosophila gene encodes a putative RNA helicase of the "DEAD box" family

Recently, a family of proteins containing the conserved motif Asp-Glu-Ala-Asp, the "DEAD box" proteins, has been identified. This family is typified by the eukaryotic translation initiation factor eIF4A, and its members are believed to share the functional property of ATP-dependent RNA unwinding. One of the previously identified members of this family (vasa) is the product of a maternally expressed gene from Drosophila melanogaster that is known to play a role in the formation of the embryonic body plan. We report here the isolation of a Drosophila gene that has an mRNA expression pattern somewhat similar to that of vasa and also encodes a DEAD box protein. We have termed this gene ME31B to reflect its maternal (ovarian germ-line) expression and its location within the 31B chromosome region. Comparisons with the other members of this family reveal that although ME31B is most like the protein Tif1/Tif2, which probably represents the Saccharomyces cerevisiae version of eIF4A, it is unlikely that ME31B represents the Drosophila eIF4A protein per se. A search for mutations in the ME31B gene has established that the P element which causes the female-sterile mutation flipper lies in the 3' flank of the ME31B gene.

Endopolyploidy in follicle epithelial cells around the nurse chamber during oogenesis in Chrysomya putoria (Diptera, Calliphoridae)

Feulgen-DNA values and nuclear areas were evaluated microspectrophotometrically for epithelial cells of the ovarian follicle during oogenesis in Chrysomya putoria. The aim was to investigate whether polyploidization occurred in the cells surrounding the nurse chamber and/or in those around the oocyte as well as whether different DNA amounts were found regarding the cell types considered. Four DNA endoreduplicative cycles could be demonstrated for the epithelial cells regardless of their localization on the follicle, during oogenesis. A small percentage of epithelial cells reaches a 32C degree. The nuclear area, however, did not increase at the same rate in cells covering the oocyte as in those covering the nurse chamber, in some of the oogenesis stages. The meaning of endopolyploidy for these cells is discussed, considering reports on relevance of secretory activities and their maintenance in polyploid cell systems.