ANALYZE STEPS CONTROLLING GENE EXPRESSION

黑腹果蝇的胚层期是细胞发育的时期

The blastoderm stage in Drosophila melanogaster is a time of cell determination and dramatic transitions in the cell cycle and in transcription. The similarities between this stage and the midblastula transition in amphibians suggests that there is a constellation of events involving the cell cycle, transcription and cell movement that is common to the early development of many organisms. We are studying these events in Drosophila because of the potential for integrating molecular with genetic analyses in this system. We have succeeded in identifying four Drosophila blastoderm specific genes: terminus (ter), polebud (pod), serendipity (sry) and bsg25A. Using standard genetic screening techniques, as well as restriction fragment length polymorphism mapping, in situ hybridization to polytene chromosomes, and P- factor mediated transformation, we will identify mutant alleles in each genes, as we have done for the delta gene of the sry locus. In so doing, we will test the relationship between ter, pod and bsg25A, and hid, slater and schlaff, respectively, all embryonic lethal mutations which map close to these genes and affect embryonic morphology. We will characterize the mutant phenotype of each gene by light and electron microscopy. The ter gene encodes a TFIIIA-like, putative DNA-binding finger. We will use antibodies to ask whether the protein is present in the nucleus and will use recombinant DNA methods to engineer the production of fusion and native ter proteins to ask whether it binds DNA in vitro. If so, we will identify specific DNA-binding sequences. We will identify the cis-regulatory sequences of the ter gene, and test the hypothesis that the gene is autoregulatory and that the finger plays a role in this regulation. We will test the significance of domains of structural similarity between the pod protein and fos oncogene protein by characterizing the spatial expression of the gene (by in situ hybridization to whole embryos and antibody staining) and asking whether the pod protein is nuclear or associated with the cytoskeleton. We will prepare a molecular map of the bsg25A locus, sequence its mRNA, and examine the spatial expression of the gene in the embryo. The analysis of these blastoderm-specific genes will provide insight into the unique events in regulation of the cell cycle, cell movement and cell commitment that occurs during early embryogenesis. The regulation of these processes is relevant to similar events and their derangement, as they occur at later times during development and in the adult organism.