The mitotic roles of dli-1 as a component of the cytoplasmic dynein motor complex and sur-7, a positive regulator of Ras/MAPK signaling during vulva development in Caenorhabditis elegans

Caenorhabditis elegans has proven to be valuable and efficient as both a genetic model system for analysis of a variety of developmental processes and as a toolkit for studying the intricacies of basic cellular biology questions. Genetic analyses have led to important, and sometimes seminal discoveries, in key developmental processes including the roles of specific signal transduction pathways in cellular proliferation and differentiation, apoptosis and the widespread use among eukaryotes of messenger RNA degradation via RNA interference (RNAi). From a cell biology perspective, the nematode gonad and developing embryo offer both a genetically tractable system for analysis of mitotic and meiotic cell-cycle and cell-division machinery, and a cell large enough to easily (and with high resolution) observe the effects of genetic manipulation of these systems.; This thesis work is divided into two parts. The first addresses the roles of a subunit of the cytoplasmic dynein motor complex. I have isolated the first mutant alleles of the light intermediate chain subunit of cytoplasmic dynein, which I have named dli-1. DLI-1, like dynein heavy chain, is required for embryonic pronuclear migration, centrosome separation and centrosome association with the nuclear envelope. However, unlike dynein heavy chain, DLI-1 does not appear to be required for earlier meiotic events. Additionally, mutational analysis of DLI-1 suggests that this protein does not function as an ATPase, as has been previously suggested.; Secondly, I describe molecular cloning and characterization of sur-7 (suppressor of r&barbelow;as), a positive regulator of the Ras/MAP kinase signal transduction pathway. Genetic analysis of sur-7 suggests that it is not a component of the canonical linear portion of the pathway, but is instead acting in a process that converges upon the Ras pathway at the level after Raf kinase. Molecular identification of the sur-7 locus led to the understanding that SUR-7 is a divergent member of the cation diffusion facilitator family of proteins. These proteins are known to regulate cellular concentrations of heavy metals and loss-of-function mutations in another C. elegans member of this family, cdf-1, are also able to suppress activated Ras. Characterization of sur-7 has more precisely defined where zinc levels affect signaling through the Ras pathway and has led to a more thorough understanding of where other regulators of this pathway, such as sur-6, exert their influence.