Elizabeth Noll

The segment polarity phenotype of Drosophila involves differential tendencies toward transformation and cell death

The segment polarity genes of Drosophila are required for intrasegmental organization, as revealed by their abnormal cuticular morphology in mutant embryos. Lesions in most of these loci result in a similar cuticular phenotype, in which the normally naked, posterior region of the segment is covered to varying degrees by ectopic denticles. A temperature-sensitive allele of armadillo, which allows us to vary the level of arm+ activity, generates this entire range of phenotypes, suggesting that these genes affect a common pathway. Previous work with a strong allele of arm revealed the locus to be cell-autonomous, in that small homozygous epidermal clones secreted denticles. We have conducted a similar clonal analysis at all levels of arm+ activity. This shows a differential tendency toward cell transformation and cell death within the segment. Antibodies to segmentation gene-fusion products show that the cell death is primarily in the most posterior region of the segment. We suggest that differential cell respecification, resulting in transformation or death, is involved in generating the segment polarity phenotype.

Paradigms to Study Signal Transduction Pathways in Drosophila

Publisher Summary This chapter discusses the mechanisms, by which groups of cells alter the developmental behavior of other cells during oogenesis and embryogenesis. It describes the processes of oogenesis and embryogenesis in Drosophila melanogaster , and how various genetic analyses have led to the characterizations of genes involved in specific cell-cell interaction processes. Signaling the pathways employed in Drosophila are strikingly similar to those of the vertebrates, so these paradigms are clearly valuable model systems to analyze evolutionarily conserved signaling pathways. These model systems can be used for “gene discovery” and subsequent identification of the mammalian homologues of novel components identified from the genetic studies. Furthermore, the Drosophila paradigms can be used as in vivo assays to test the specific hypotheses drawn from the biochemical studies. The examples described in this chapter provide simple paradigms to identify the components that operate in specific signaling pathways and to dissect the details of how the signals are transduced. This chapter also discusses some of the molecular pathways used to build the egg and to pattern the embryo. These evolutionarily conserved pathways provide unique paradigms to apply the genetic tools to identify the novel components and characterize their functions.