Typescript. / Bibliography: leaves 149-163. / Microfiche. / xvi, 163 leaves ill

Thesis (Ph. D. in Biological Sciences)--Vanderbilt University, May 2007. / Title from title screen. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 278-289). Available also in a digital version from Dissertation Abstracts.

No description available.

Thesis (Ph. D.)--University of Chicago, 1908. / "The Journal of morphology--vol. XX, no. 1." Each plate accompanied by leaf with descriptive text. "Literature cited": p. 121-123.

Thesis (Ph. D.)--University of Chicago, 1908. / "The Journal of morphology--vol. XX, no. 1." Each plate accompanied by leaf with descriptive text. "Literature cited": p. 121-123. Also available on the Internet. Also issued online.

Universiẗat, Diss., 2003--Köln.

Gastrulation is a key early developmental event that generates the three primary germ layers (ectoderm, mesoderm, and endoderm) from which organ systems subsequently develop. The physical mechanisms of germ layer formation differ significantly in amniotes (reptiles, birds, and mammals) and anamniotes (e.g. frog and fish), as amniote gastrulation includes an epithelial-mesenchymal transition (EMT) that is absent from anamniote gastrulation. Despite this striking difference, much of our knowledge regarding the mechanisms underlying gastrulation is derived from frog and fish studies. To better understand amniote gastrulation, the work herein investigates three signaling pathways that regulate amniote gastrulation with distinct and overlapping functions. The central hypothesis is that multiple signaling pathways function cooperatively to precisely modulate cell migration through the primitive streak during avian gastrulation.First, I describe a novel function of Fibroblast Growth Factor (FGF) signaling in the preingression epiblast adjacent to the avian primitive streak, where it governs the expression of molecules from diverse signaling pathways and transcription factor families, and which is mediated largely through the Ras/MAPK pathway. Importantly, FGF signaling also regulates cell migration during avian gastrulation.Next, I report the isolation of a novel chicken non-canonical Wnt ligand (Wnt11b) that is specifically expressed in the primitive streak and adjacent preingression epiblast during gastrula stages. In gain and loss of function studies, Wnt11b and Wnt5a/b participate in regulating cell migration through the streak in a largely redundant fashion. Signaling specifically targets the non-canonical pathway, as similar cell migration defects are observed with a non-canonical mutant of Dishevelled, and activating the canonical pathway has no effect on cell migration.Finally, I investigate the function of A-class Eph-ephrin signaling during avian gastrulation, and describe that Eph receptor forward signaling negatively regulates the migration of cells through the primitive streak. This modulation of cell migration occurs independently of the EMT that accompanies avian gastrulation, as cells are able to undergo the normal cadherin transition and the basal lamina is unaffected.Altogether, the work presented herein provides a significant contribution to our understanding of signaling pathways that modulate gene expression and ongoing cell migration during germ layer formation in amniote gastrulation.

No description available.

During early development of Xenopus laevis, gastrulation is a key morphogenetic event which transforms the embryo into three of primary germ layers: ectoderm, mesoderm, and endoderm. In order for the physical separation of these layers to occur, cells have to acquire specific properties that distinguish one layer from another. These properties, which include cell adhesion and migration, should be reflected in the tissue-specific proteome. While genetic analysis has led to the determination of a number of proteins involved in germ layer formation, this method would not have identified those proteins regulated on a translational or post-translational level. In this study, we have developed a two-dimensional gel based comparative proteomic approach employing difference gel electrophoresis (DiGE) to identify proteins involved in germ layer morphogenesis during Xenopus gastrulation. Differences between the physical properties of the ectoderm and mesoderm are likely based on differences in the proteomes of the cell surface and/or cortex. We therefore analyzed plasma membrane enriched fractions, obtained using discontinuous sucrose density gradient centrifugation. The Decyder program was used to quantify expression changes with statistical confidence across multiple DiGE gels, provide independent confirmation of distinct expression patterns from the individual experiments, and demonstrate high reproducibility between replicate samples. The identity of 23 proteins, which were obtained from 33 analyzed spots, was determined using mass spectrometry. Our proteomic analysis of Xenopus ectoderm and mesoderm identified alterations in proteins involved in cytoskeletal organization, signal transduction, protein folding, vesicle trafficking, and in glycolysis. We have also demonstrated the feasibility of proteomics in Xenopus, and have therefore shown that proteomics may be a valuable tool for analysis of early development in this system.