Browsing by Subject "Cells--Growth"
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Item Genetic interactors of the Cdc42 GTPase effectors Gic1 and Gic2: their identification and functions in budding yeast cell polarity(2004) Gandhi, Meghal Kanaiyalal; Chan, Clarence S. M.Gic1 and Gic2 are structurally and functionally related effectors of the evolutionarily conserved Cdc42 GTPase in Saccharomyces cerevisiae. Like many other effectors of Cdc42, Gic1 and Gic2 function in the process of polarized cell growth. In the absence of both Gic1 and Gic2, yeast cells exhibit depolarized actin cytoskeleton and polarized growth defects at elevated temperatures. To obtain further insight into the biological role of Gic1 and Gic2, genetic approaches were used to identify functionally interacting partners of these proteins. A screen for multi-copy suppressors of the temperature-sensitivity of gic1 gic2 cells identified many genes (including AXL2, BNI1, CLN2, MSB1, MSB2, RSR1 and STE20) that have known roles in polarized cell growth. In addition, two pairs of structurally related genes - VHS2 and MLF3, MGC1 and TOS2 - with no previously reported functions were also identified. Functional characterization of VHS2 and MLF3 revealed their role in a pathway that affects the actin cytoskeleton organization and cell wall integrity. This pathway is functionally redundant to that mediated by GIC1 and GIC2. Functional characterization of MGC1 and TOS2 indicated that these genes function in the process of polarized growth, particularly in the process of cytokinesis. A genome-wide Synthetic Genetic Analysis identified more than 30 nonessential genes as those whose function overlaps with that of GIC1 and GIC2. Mutation in each of these genes exacerbates the growth defect of gic1 gic2 cells. As expected, some of these genes are involved in polarity-related functions, such as actin cytoskeleton organization, bud-site selection and cell wall biosynthesis. Others participate in a variety of biological processes, including organelle biogenesis, secretion and vesicular transport. The latter finding suggests that GIC1 and GIC2 may have function outside the scope of actin cytoskeleton organization. Taken together, the work presented here has uncovered the function of four previously uncharacterized genes in polarized cell growth. It has also provided hints to additional potential functions of GIC1 and GIC2. Further exploration of these functions might provide important links between Cdc42 signaling and cellular processes such as organelle biogenesis, secretion and vesicular transport, all of which need to be executed coordinately during polarized cell growth.Item Novel roles of the proteins Oskar and Bluestreak in germ cell formation and migration(2007) Jones, Jennifer Rebecca, 1978-; Macdonald, Paul M.The formation of germ cells in Drosophila melanogaster is dependent on the presence of ribonucleoprotein complexes called polar granules. A key component of these complexes is Oskar, a novel protein which has been shown to nucleate the granules. To investigate whether Oskar plays a further role in polar granule formation, I cloned the oskar gene from D. immigrans flies (osk[superscript imm]) and introduced it into D. melanogaster flies using P-element transformation. I found that osk[superscript imm] was able to rescue both the posterior patterning and germ cell formation defects of embryos from oskar mutant mothers. In addition, I found that the polar granules of embryos containing only Osk[superscript imm] as a source of Oskar protein resemble those found in D. immigrans embryos, indicating a new role for Oskar in determining the morphology of the polar granules. Germ cell formation in Drosophila is succeeded by migration of the germ cells to the site of gonad formation. A second line of research presented in this dissertation describes analysis of a novel protein important for both germ cell formation and migration, Bluestreak (Blue). Embryos from either heterozygous or homozygous Blue-mothers display defects in germ cell number and shape. I found that the ovaries of Blue-females have defects in the localization of Staufen and Oskar, sufficient to cause a reduction in pole cell number in embryos. In addition, genetic analysis of the interaction between Bluestreak and mutants which affect pole cell migration implicates Bluestreak in this process. Finally, I found that Blue localizes to centrosomes along with [gamma]-tubulin throughout the embryo, and to the nuclear membrane in pole cells. My findings introduce the possibility that Bluestreak may act to regulate germ cell migration in Drosophila.