In organisms ranging from bacteria to mammals, certain cells undergo reproducible patterns of division during development and growth. The division pattern is important for morphogenesis, tissue organization, and cellular interactions that influence developmental fate. The orientation of division also plays a role in the segregation of cellular components during intrinsically asymmetric divisions. Thus, an understanding of how division patterns are controlled is essential to our understanding of basic developmental processes, including those of humans, and could aid in our understanding of developmental disorders. We are studying the control of cell division pattern using the nematode C. elegans, which is amenable to genetic, morphological and molecular analysis. We are using a genetic approach to identify genes required for the normally invariant cell division pattern of the C. elegans embryo. Our long term goals are to characterize the defects associated with removal of those gene's activities, and isolate and study the genes at the molecular level. The specific goals of this proposal are 1) to determine when and where let-99 (a gene we have shown is critical for normal division orientation) and a related gene Irg-1, are expressed, 2) elucidate the role of let-99 and Irg-1 in division orientation and other aspects of development, and 3) begin the study of other genes involved in controlling division orientation. To accomplish these aims, we will use developmental RNA blots to determine when the let-99 and Irg-1 genes are expressed. We will use LET-99 and LRG-1 antisera to determine when and in what cells the proteins are present, and whether the proteins are localized to any subcellular structures that would give insight into function. We will characterize additional let-99 mutations (and isolate null alleles if necessary) to address whether let-99 is required for division orientation at times other than early embryogenesis. To determine if Irg-1 is required for division orientation or other aspects of development, we will generate Irg-1 mutations using target-selected mutagenesis and characterize the mutant phenotype Finally, we propose to continue genetic screens for mutations that alter the division pattern of the embryo, in order to isolate alleles of new genes s well as additional alleles of genes we previously identified. The characterization of a subset of the new mutations will be initiated.
