http://hdl.handle.net/1721.1/7589 Wed, 19 Jun 2013 13:59:26 GMT 2013-06-19T13:59:26Z http://hdl.handle.net/1721.1/79321 Oocyte differentiation is genetically dissociable from the meiotic program in mice Dokshin, Gregoriy A. (Gregoriy Aleksandrovich) Oogenesis is a developmental program by which a gametogenesis-competent germ cell becomes a fertilization-competent egg. During oogenesis, growth and differentiation of oocytes are closely coordinated with initiation and progression through meiosis. In mammals, the timing of meiotic initiation is sexually dimorphic, with only ovarian and not testicular germ cells initiating meiosis during fetal development. Consequentially, fetal meiotic initiation is thought to be prerequisite to subsequent growth and differentiation of the ovarian germ cell into a fully grown oocyte. Here I present evidence that meiotic initiation and prophase I are genetically separable from oocyte growth and differentiation, thereby, demonstrating that oogenesis consists of two independent processes under separate regulation. This represents a novel view of the oogenesis program and revises the current model of germ cell commitment to oogenesis in mice. The proposed revised model accounts for independent commitment of a germ cell to meiosis and differentiation. This model may provide insights into previously unexplained cases of female infertility and has practical implications for in vitro oogenesis strategies. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 2013.; Cataloged from PDF version of thesis. Page 100 blank.; Includes bibliographical references. Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/1721.1/79321 2013-01-01T00:00:00Z http://hdl.handle.net/1721.1/79293 Marine microbial intact polar diacylglycerolipids and their application in the study of nutrient stress and bacterial production Popendorf, Kimberly J. (Kimberly Julia) Intact polar diacylglycerolipids (IP-DAGs) were used to study microbial dynamics in the surface ocean. IP-DAGs from surface ocean seawater were quantified using high performance liquid chromatography-mass spectrometry (HPLC-MS), after first developing a sensitive, high throughput molecular ion independent triple quadrupole MS method for quantification. Using this analytical technique I examined the distribution of the nine most abundant classes of IPDAGs across the Mediterranean, and found that phospholipids as a percent of total IP-DAGs correlated with phosphate concentration. Furthermore, phospholipids were a higher percent of total particulate phosphorus where phosphate was higher, ranging from 1-14%. Thus IP-DAGs can play not only a significant but also a dynamic role in defining planktonic nutrient needs and cellular C:N:P ratios in the environment. Additionally, microcosm incubations were amended with phosphate and ammonium, and in the course of several days this elicited a shift in the ratios of IP-DAGs. This study was the first to demonstrate the dynamic response of membrane lipid composition to changes in nutrients in a natural, mixed planktonic community, and indicated that the change in IP-DAG ratios in response to changing nutrients may be a useful indicator of microbial nutrient stress. In the surface waters of the western North Atlantic I used three experimental approaches to identify the microbial sources of the nine most abundant classes of IP-DAGs. Phytoplankton are the primary source of one class of sulfolipid, sulfoquinovosyldiacylglycerol, and one class of betaine lipid, diacylglyceryl-trimethyl-homoserine, while heterotrophic bacteria are the dominant source of the phospholipids phosphatidylglycerol and phosphatidylethanolamine. In regrowth experiments in the Sargasso Sea and the North Pacific I demonstrated that phospholipid specific production rate is representative of heterotrophic bacterial cell specific growth rate. I measured phospholipid specific production rate and bacterial production rate using uptake of 3H-leucine (³H-Leu) and 3H-thymidine (³H-TdR) across the North Atlantic, across the Mediterranean, and in the North Pacific subtropical gyre. I found that phospholipid specific production rates estimate heterotrophic bacterial cell specific growth rates that are on the order of 1 per day, an order of magnitude faster than cell specific growth rates suggested by uptake of ³H-Leu and ³H-TdR. 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), February 2013.; "February 2013." Cataloged from PDF version of thesis.; Includes bibliographical references. Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/1721.1/79293 2013-01-01T00:00:00Z http://hdl.handle.net/1721.1/79284 Advances in measurements of particle cycling and fluxes in the ocean Owens, Stephanie Anne The sinking flux of particles is an important removal mechanism of carbon from the surface ocean as part of the biological pump and can play a role in cycling of other chemical species. This work dealt with improving methods of measuring particle export and measuring export on different scales to assess its spatial variability. First, the assumption of ²³⁸U linearity with salinity, used in the ²³⁸U-²³⁴Th method, was reevaluated using a large sample set over a wide salinity range. Next, neutrally buoyant and surface-tethered sediment traps were compared during a three-year time series in the subtropical Atlantic. This study suggested that previously observed imbalances between carbon stocks and fluxes in this region are not due to undersampling by traps. To assess regional variability of particle export, surface and water-column measurements of ²³⁴Th were combined for the first time to measure fluxes on ~20 km scales. Attempts to relate surface properties to particle export were complicated by the temporal decoupling of production and export. Finally, particle export from ²³⁴Th was measured on transects of the Atlantic Ocean to evaluate basin-scale export variability. High-resolution sampling through the water-column allowed for the identification of unique ²³⁴Th features in the intermediate water column. 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), 2013.; Cataloged from PDF version of thesis.; Includes bibliographical references. Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/1721.1/79284 2013-01-01T00:00:00Z http://hdl.handle.net/1721.1/79191 The oocyte-to-embryo transition : regulation of oocyte maturation and egg activation in Drosophila Weingarten, Lisa Suzanne In oogenesis, meiosis must be highly regulated to ensure that growth of the oocyte and chromosomal segregation are coordinated properly. To do this, meiosis arrests at two points to permit oocyte differentiation and coordination with fertilization. In Drosophila, the first arrest in prophase I is released by oocyte maturation, and the second arrest in metaphase I is released by egg activation. This thesis explores mechanisms controlling these two processes. First, the putative role of the Deadhead (DHD) thioredoxin in Drosophila female meiosis is examined. Possible roles that DHD may play in DNA replication, ROS/RNS redox pathways, and vitelline membrane crosslinking are explored. Furthermore, current research into the role of Ca²+ as a regulator of Drosophila egg activation is summarized. Recent studies have suggested that Sarah (Sra), a regulator of Calcineurin (CN), is required for egg activation and meiotic completion. A model for Sra/CN signaling is presented, highlighting the role of Ca²+ in Drosophila activation, and emphasizing aspects of meiotic activation conserved across species. Finally, proteins recovered from a large-scale proteomic screen undertaken by our lab are discussed. This screen identified proteins that increase or decrease significantly during the processes of maturation and activation through quantitative mass spectrometry. Pairwise comparison of protein levels between pre- and post- maturation oocytes (stage 10 vs. stage 14 oocytes) or pre- and post-activation eggs (stage 14 vs. unfertilized eggs) identified candidate proteins up- and downregulated during one or both of these processes. These candidates include proteins involved in calcium binding and transport, the ubiquitination pathway, steroid biosynthesis and metabolism, and a gap junction protein. Additional characterization of these proteins may provide further insight into the regulation of Drosophila maturation and activation. Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Biology, 2013.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 33-39). Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/1721.1/79191 2013-01-01T00:00:00Z