9511201 Lai A long term objective of Dr. Lai's research is to elucidate the inhibitory mechanisms of cell fate determination and cellular differentiation. Inhibitory signal transduction plays a critical role in development, but little is known about the mechanisms. Using the Drosophila eye system, a negative nuclear regulator of photoreceptor cell specification, the product of the yan gene, has been previously characterized. Dr. Lai hypothesizes that Yan normally acts to maintain photoreceptor precursor cells in an undifferentiated state, and such inhibition can be overcome by proneural signalling, for example, the Sevenless tyrosine receptor kinase and Ras1 protein that promote the development of photoreceptor cell. To understand how Yan acts to maintain precursor cells undetermined, and to reveal the functional significance of negative control in nuclear signal transduction, Dr. Lai's team will use a combination of genetic, molecular and cellular approaches. The specific aims include: 1) a genetic screen for Enhancers of yan, 2) genetic characterization of E(yan) mutations, and 3) molecular cloning of E(yan) genes. To accomplish these aims, a sensitized and efficient assay has been devised by Dr. Lai for identifying mutations that interact with yan. Selected E(yan) genes will be genetically and molecularly characterized. Methods to be used include mutagenesis of the Drosophila genome, phenotypic analysis of isolated mutations, molecular cloning and a P transposon mediated transformation. The Drosophila photoreceptor cell provides an amenable system for molecular genetic studies of key regulators of development. The work proposed here will lead to the identification of key inhibitory regulators of cell fate determination, whose structural information can be used for identifying their vertebrate homologues. It will yield valuable information on how negative control is integrated into the regulatory hierarchy of signal transduction in the nucleus. ***
