Functional characterization of calliphorid cell death genes and cellularization gene promoters for controlling gene expression and cell viability in early embryos

The New World screwworm fly, Cochliomyia hominivorax, and the Australian sheep blow fly, Lucilia cuprina, are major pests of livestock. The sterile insect technique was used to eradicate C. hominivorax from North and Central America. This involved area-wide releases of male and female flies that had been sterilized by radiation. Genetic systems have been developed for making 'male-only' strains that would improve the efficiency of genetic control of insect pests. One system involves induction of female lethality in embryos through activation of a pro-apoptotic gene by the tetracycline-dependent transactivator. Sex-specific expression is achieved using an intron from the transformer gene, which we previously isolated from several calliphorids. In the present study, we report the isolation of the promoters from the C. hominivorax slam and Lucilia sericata bnk cellularization genes and show that these promoters can drive expression of a GFP reporter gene in early embryos of transgenic L. cuprina. Additionally, we report the isolation of the L. sericata pro-apoptotic hid and rpr genes, identify conserved motifs in the encoded proteins and determine the relative expression of these genes at different stages of development. We show that widespread expression of the L. sericata pro-apoptotic genes was lethal in Drosophila melanogaster. The isolated gene promoters and pro-apoptotic genes could potentially be used to build transgenic embryonic sexing strains of calliphorid livestock pests.

Organization and expression of the Australian sheep blowfly (Lucilia cuprina) hsp23, hsp24, hsp70 and hsp83 genes

In this study we report the isolation and characterization of a heat shock protein 70 (hsp70) gene, the hsp83 gene and two genes that encode small Hsps (Lchsp23 and Lchsp24) from the Australian sheep blowfly, Lucilia cuprina, a major agricultural pest. Phylogenetic analyses indicate that the LcHsp23 protein is the orthologue of Drosophila melanogaster Hsp23 and LcHsp24 is the orthologue of Sarcophaga crassipalpis Hsp23. Quantitative reverse-transcriptase PCR analysis showed that the basal level of Lchsp83 RNA is relatively high at all developmental stages and only moderately induced by heat shock. In contrast, Lchsp70 transcripts are present at low levels and strongly induced by heat shock at all stages. The basal levels of expression and degrees of heat induction of the Lchsp23 and Lchsp24 transcripts were more variable across the different developmental stages. Putative heat shock factor binding sites were identified in the Lchsp24, Lchsp70 and Lchsp83 gene promoters. The isolation of these hsp gene promoters will facilitate constitutive or conditional expression of a gene of interest in transgenic Lucilia.

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.

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

Working with the large dipteran Calliphora erythrocephala, we have performed differential screening to identify genes actively expressed in the previtellogenic and early vitellogenic stages of oogenesis but silent during the early stages of embryogenesis. Clones containing sequences homologous to four such genes have been characterized. Two clones are homologous to the yolk protein 1 gene of Drosophila melanogaster. These two clones are expressed not only in the columnar follicle cells surrounding the oocyte but also in the border cells--a highly specialized subgroup of the follicle cells. This indicates a new function for these cells though previously to contribute mainly in the formation of the micropyle. A third clone, which is related to the D. melanogaster vitelline membrane protein genes of the cluster at chromosomal locus 26A, is expressed only in the perioocyte follicle cells and not the border cell population. The fourth clone encodes a sequence of unknown function which is abundantly expressed in the germ line cells of the follicle. Transcripts homologous to this clone persist into the mature follicle and initially appear concentrated at the anterior pole of the oocyte. The distribution of repetitious DNA within these four clones indicates that the C. erythrocephala genome has a short interspersion arrangement of repetitive DNA.

Both nucleolar organizers are replicated in Dipteran polyploid tissues: a study at the level of individual nuclei

Working with the Dipteran Calliphora erythrocephala, we have tested the hypothesis that only one nucleolar organizer region (NO) is replicated during polyploidization. NO replication was examined in two very different highly polyploid nuclear types: salivary gland nuclei and nurse cell nuclei. Two strains of the organism containing NO regions with highly diagnostic nontranscribed spacer (NTS) polymorphisms were prepared and reciprocal single pair-matings between members of the strains were performed. The representation of the two distinguishable NOs in diploid and polyploid DNAs of individual F1 progeny from each cross was then examined. DNA from a total polyploid nuclear DNA preparation and from individual polyploid nuclei of both tissue types was analyzed. Our results show conclusively that both genomic NOs are replicated in individual polyploid nuclei of both types. Further, evidence for variation in the relative replication of cistrons from the two NOs by individual nuclei was obtained. The cistron types present in the NOs of both strains showed differential replication upon polyploidization. In general, the patterns of differential cistron replication seen in salivary gland and nurse cell nuclei were similar.