http://hdl.handle.net/1721.1/7589 2013-05-23T06:43:08Z http://hdl.handle.net/1721.1/77851 Mechanism of DNA chain initiation by the dnaG protein of Escherichia coli Capon, Daniel Jeffrey Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Biology, 1981.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.; Bibliography: leaves 174-182. 1981-01-01T00:00:00Z http://hdl.handle.net/1721.1/77786 The auditory system of the minke whale (Balaenoptera acutorostrata) : a potential fatty sound reception pathway in a mysticete cetacean Yamato, Maya Despite widespread concerns about the effects of anthropogenic noise on baleen whales (suborder Mysticeti), we lack basic information about their auditory physiology for comprehensive risk assessments. Hearing ranges and sensitivities could be measured if customized equipment and methods were developed based on how baleen whales receive sound. However, sound reception pathways in baleen whales are currently unknown. This thesis presents an integrative approach to understanding hearing in baleen whales through dissections, biomedical imaging, biochemical analyses, and modeling sound propagation through a whale head using the Finite Element Method (FEM). We focused on the minke whale (Balaenoptera acutorostrata) because it is one of the smallest and most abundant mysticete species, reducing logistical difficulties for dissections and experiments. We discovered a large, well-formed fat body extending from the blubber region to the ears and contacting the ossicles. Although odontocetes, or toothed whales, are thought to use specialized "acoustic fats" for sound reception, no such tissues had been described for mysticetes to date. Our study indicates that the basic morphology and biochemical composition of the minke whale "ear fats" are very different from those of odontocete acoustic fats. However, the odontocete and mysticete fatty tissues share some characteristics, such as being conserved even during starvation, containing fewer dietary signals compared to blubber, and having well-defined attachments to the tympano-periotic complex, which houses the middle and inner ears. FE models of the whale head indicated that the ear fats caused a slight increase in the total pressure magnitude by the ears, and this focusing effect could be attributed to the low density and low sound speed of the ear fats in the models. Fatty tissues are known to have lower densities and sound speeds than other types of soft tissues, which may explain why they are an important component of the auditory system of odontocetes, and perhaps mysticete cetaceans as well. In an aquatic habitat where the pinna and air-filled ear canal are no longer effective at collecting and focusing so'und towards the ears, we propose that both odontocete and mysticete cetaceans have incorporated fatty tissues into their auditory systems for underwater sound reception. Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references. 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/77781 Germ cell nuclear factor is not required for the down-regulation of pluripotency markers in fetal ovarian germ cells Okumura, Leah M In mouse, germ cells retain expression of the pluripotency markers Oct4 and Nanog longer than any other cells in the body. While somatic cells repress these markers during gastrulation, female germ cells continue to express them until around the time of meiotic initiation. It is not yet clear why pluripotency markers are downregulated with this particular timing, nor is it understood what factors are involved in their repression. I have examined in fetal ovarian germ cells the expression and function of Gcnf (germ cell nuclear factor), an orphan nuclear receptor known to regulate both Oct4 and Nanog in gastrulating embryos. I have found that Gcnf is expressed in a female germ-cell-specific manner at the time when Oct4 and Nanog are down-regulated there. Gcnf mutants in which the ligand binding domain is disrupted display defects after gastrulation comparable to those observed in Gcnf-null mutants and those lacking the DNA binding domain. In contrast, the germ cells Gcnfligand binding domain mutants show no failure in repression of pluripotency markers, and other aspects of female germ cell development appear normal as well. Thus, it appears that the ligand binding domain of GCNF is not required for fetal ovarian germ cell development. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references. 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/77639 Spatial and temporal coordination of genome segregation with activation of the Mitotic Exit Network Rock, Jeremy M. (Jeremy Michael) In budding yeast, an essential Hippo-like signal transduction cascade known as the Mitotic Exit Network (MEN) governs the final cell cycle transition, the mitosis to G1 transition. To ensure the accurate execution of mitosis, MEN activity is coordinated with other cellular events. The work presented in this thesis elucidates the coordination of genome segregation with MEN activation. We first identified a novel essential role for Polo kinase Cdc5 in MEN activation. Cdc5 functions in parallel to the GTPase Tem1 to recruit the MEN kinase Cdc15 to SPBs, which is both necessary and sufficient for MEN signaling. This work thus defined Cdc15 as a coincidence detector of two essential cell cycle oscillators: the Polo kinase Cdc5 synthesis/degradation cycle and the Tem1 G-protein cycle. The Cdc15-dependent integration of these temporal (Cdc5 and Tem1 activity) and spatial (Tem1 activity) signals ensures that exit from mitosis occurs only after proper genome partitioning. Finally, we characterize the role of the scaffold Nud1 in the assembly of active MEN signaling complexes at spindle pole bodies (SPBs). We found that the assembly of such complexes requires the phosphorylation of the MEN scaffold Nud1. Phosphorylation of Nud1 in mitosis is essential for the SPB recruitment of terminal MEN kinase Dbf2 and its coactivator Mob1. We further show that the Hippo-like kinase Cdc15 phosphorylates Nud1. Finally, we present evidence that Mob1 is a novel class of phosphopeptide binding domains. Thus, Cdc15-dependent phosphorylation of the scaffold Nud1 creates a docking site for the Mob1 coactivator, thereby resulting in the recruitment of Dbf2 to SPBs and firing of the MEN. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 2012.; This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.; Cataloged from student-submitted PDF version of thesis.; Includes bibliographical references. 2012-01-01T00:00:00Z