Transplantation of nucle in Drosophila melanogaster

Glyoxal-based fixation of Drosophila embryos for immunofluorescence staining and RNA in situ hybridization

The dialdehyde glyoxal is an alternative chemical fixative that cross-links tissues faster than formaldehyde, retains higher antigenicity, and is less hazardous than either formaldehyde or glutaraldehyde. Here we present a glyoxal-based fixation protocol for use with Drosophila embryos. We describe steps to prepare acid-free glyoxal, fix embryos, and then stain with antibodies for immunofluorescence (IF). We also describe methods for RNA fluorescence in situ hybridization (FISH) and FISH plus IF (FISH-IF) using glyoxal-fixed embryos. This protocol was adapted for Drosophila embryos from the methods of Bussolati et al.1 and Richter et al.2.

A novel Cre/loxP system for mosaic gene expression in the Drosophila embryo

BACKGROUND

Mosaic analysis is used to assess gene function and cell autonomy in a subset of cells in an organism, and has been extensively applied in Drosophila studies. However, it is difficult to generate mosaic cells in Drosophila embryonic tissues using existing methods. Therefore, we developed a new method for generating genetic mosaic embryos using a modified Cre/loxP system. In this report, we also characterized the capabilities and limitations of this novel method.

RESULTS

We first constructed a novel cassette combining loxP with the Actin 5C enhancer and Gal4 cDNA, and generated a transgenic fly carrying this construct (Aloxg-Gal4). In Aloxg-Gal4, the activation of Gal4 expression is suppressed by the gypsy insulator. Once the gypsy insulator is removed, however, Gal4 is expressed when site-specific recombination between loxP sites is induced by Cre recombinase. This system allowed the mosaic expression of Gal4 in Drosophila embryonic tissues (epidermis, amnioserosa, tracheal system, malpighian tubules, foregut, hindgut, midgut, and neuron), leading to the Gal4-dependent activation of arbitrary genes under the control of the upstream activation sequence (UAS).

CONCLUSIONS

This practical method can be used to generate mosaic cells in Drosophila embryonic tissues and can be applied to any gene without specialized equipment.

Chimeric honeybees (Apis mellifera) produced by transplantation of embryonic cells into pre-gastrula stage embryos and detection of chimerism by use of microsatellite markers

The production of chimeras, by use of cell transplantation, has proved to be highly valuable in studies of development by providing insights into cell fate, differentiation, and developmental potential. So far, chimeric honeybees have been created by nuclear transfer technologies. We have developed protocols to produce chimeric honeybees by use of cell transplantation. Embryonic cells were transplanted between pre-gastrula stage embryos (32-34 hr after oviposition) and hatched larvae were reared in vitro for 4 days. Chimeric individuals were detected by use of microsatellite analysis and a conservative estimation approach. 4.8% of embryos, posteriorly injected with embryonic cells, developed into chimeric honeybee larvae. By injection of cells pre-stained with fluorescent cell tracer dye, we studied the integration of transplanted cells in the developing embryos. Number of injected cells varied from 0 to 50 and cells remained and multiplied mainly in the area of injection.

Identification of germ plasm-enriched mRNAs in Drosophila melanogaster by the cDNA microarray technique

The development of embryonic germ cells in Drosophila depends on the germ plasm, the most posterior part of the ooplasm. The germ plasm is devoted to the formation of future germ cells and is known to contain all the factors that are necessary to induce germ cell fate. Besides having a characteristic organelle and protein distribution, the germ plasm also contains a large number of localized RNA species that have been shown to play crucial roles in germ cell determination. To identify germ plasm-enriched, localized transcripts, we used a two-step method composed of cDNA microarray (containing 3200 annotated Drosophila cDNAs) and in situ RNA hybridization techniques. We compared germ plasm deficient, normal and ectopic germ plasm conditions in the cDNA microarray experiments. RNA species whose concentration increased when ectopic germ plasm was present and decreased when the germ plasm was missing were selected. These candidates were then subjected to a second screen which compared the distribution of the given RNA in wild type embryos and in eggs with ectopic germ plasm. Finally, 17 RNA species were found to be enriched in the germ plasm. Based on these data, we estimate that around 1% of the Drosophila genes encode for germ plasm-enriched, localized transcripts. We conclude that this combination of microarray and in situ hybridization techniques is a simple but powerful experimental design for the genome-wide identification of genes coding for germ plasm localized transcripts.

Chimaeras of Drosophila melanogaster obtained by injection of haploid nuclei

Since the observation by Bridges of a few mosaics containing haploid tissue in Drosophila, specimens supposedly haploid have rarely been found. A technique for the easy production of haploid animals or tissues could have important applications. We have now successfully designed such a technique by the production of chimaeras obtained by transplantation of haploid nuclei from a maternal effect mutant that produces haploid embryos. We have used this technique to test the proposal of Jack and Judd that the zeste locus of Drosophila melanogaster cannot repress the activity of unpaired alleles at the white locus.

Gene transfer in Drosophila melanogaster: genetic transformations induced by the DNA of transformed stocks

DNA prepared from transformed stocks ofDrosophila melanogasterinduces second-step transformations resembling the original. The gross yield of transformants induced by transformed DNA is several times higher than that induced by the original allo-DNA, but much of this high frequency is attributable to a few exceptionally large clusters of transformants among flies treated with transformed DNA. When these large clusters are omitted from the data, the frequency of transformants induced by DNA from transformed stocks is the same as that induced by allo-DNA. The data therefore support the conclusion that the original DNA-induced alterations resulted from the transfer of genetic material capable of indefinite replication.

[RNA-Synthesis in telotrophic meroistic ovarioles of dysdercus intermedius DIST. (heteroptera, pyrrhoc.)]

RNA in insect ovaries was investigated by polyacrylamide gel electrophoresis to study site of synthesis, transportation and incorporation in mature eggs. Telotrophic-meroistic ovarioles ofDysdercus intermedius were selected for this work since they could be dissected in distinct portions: the apical one with polyploid nurse cells and the vitellarium with oocytes covered by a follicular epithelium. RNA was labeled by injecting radioactive precursors or incubating isolated ovarioles in vitro.In nurse cells labeled rRNA, tRNA and non-ribosomal RNA were found and evidence was presented for the processing of a 39s rRNA precursor molecule in 2 steps (36s and 32s) into 28s rRNA while the 18s rRNA was directly derived from the 36s molecule. A low concentration (0.5 Μg/ml) of α-Amanitin inhibited synthesis of non-ribosomal RNA thereby revealing a more distinct processing pattern for rRNA, while a high concentration (5 Μg/ml) blocked processing at the 36s molecule and led to its accumulation. Appropriate concentrations of Actinomycin D inhibited rRNA synthesis while distinct peaks of non-ribosomal RNA became apparent.RNA synthesized in the follicular cells was similar to the RNA made in the nurse cells only in the high molecular weight RNA. Some material, tentatively named "nucleotide fraction", with a mobility higher than tRNA was detected and could be localized in yolk granules. It was separable from RNA by chromatography on Sephadex G 100 and had an absorption maximum at 255 run. The "nucleotide fraction" could be rapidly labeled. It seemed to be utilized in RNA synthesis during embryogenesis. Mature eggs contained a relatively high amount of the "nucleotide fraction". If a single injection with precursor was done 4 days before analysing the RNA of mature eggs most of the label was found in the "nucleotide fraction". Eggs collected 5-8 days after injection contained only high molecular labeled RNA. This observation correlated well with the timing of egg maturation. It takes 4 days for a group of oocytes to reach the distal part of the vitellarium where yolk production and maturation go on for another 4 days. It is apparent, therefore, that the follicular epithelium contributes the "nucleotide fraction" to the oocyte, while most of the other RNA, including a stable polydisperse class of RNA, is made in the nurse cells and is transported into the oocyte.

Mode and timing of body pattern formation (Regionalization) in the early embryonic development of cyclorrhaphic dipterans (Protophormia, Drosophila)

1. Eggs of the blowflyProtophormia spec. were separated into anterior and posterior fragments of varying sizes. The operations were carried out between oviposition and the blastoderm stage. The partial larvae produced by the fragments were scored for the cuticular pattern they had formed. 2. The cuticle of the 1st instar larva carries 11 denticle belts which correspond to the anterior borders of the thoracic and abdominal body segments. These are considered the elements of a linear longitudinal pattern which starts with the head region. 3. Egg fragments of the sizes studied did not produce the complete cuticular pattern. 4. If denticle belts were present on the partial larvae formed in egg fragments, these always included the corresponding terminal pattern element (no. 1 in anterior, no. 11 in posterior fragments). Bigger partial patterns from anterior fragments may have any belt up to no. 10 as their most posterior belt, posterior partial patterns may start anteriorly with any belt up to no. 1, i.e. behind the head region. 5. After fragmentation during early stages of development, all eggs fail to form some pattern elements. Fragmentation thus causes a gap in the pattern. Extent and position within the pattern of this gap depend on level and stage of fragmentation. 6. With increasing egg age (developmental stage) at fragmentation, the gap in the cuticular pattern becomes progressively smaller. Eggs fragmented during or after formation of the blastodermal cell walls as a rule form all pattern elements. 7. The progressive reduction of the gap in the cuticular pattern is due to formation of bigger sets of pattern elements inboth partner fragments. I.e. on the average an anterior or posterior fragment of given size will produce more pattern elements if separated from the rest of the egg at a later stage than if separated early. 8. In order to produce a given set of pattern elements, a fragment needs to be bigger on the average when separated early than when separated later on. This applies to both anteriorand posterior fragments of the fragmentation levels studied. 9. According to these results, the egg ofProtophormia cannot be considered a mosaic of determinants for the different pattern elements at oviposition. The developmental fate of at least the more equatorial egg regions appears to become specified epigenetically during the period between oviposition and blastoderm formation. 10. Once the egg has become subdivided into blastoderm cells, it reacts as a developmental mosaic with respect to the pattern studied. 11. Preliminary results inDrosophila are compatible with these conclusions. 12. The results are compared to those obtained from other insect groups, and formal models for their interpretation are discussed. Pattern specification by interaction of terminal egg regions can be considered the common denominator for a number of egg types. 13. The results demonstrate that formally comparable processes of pattern formation occur in different insect egg types at different stages of development.