Thesis (M.S.)--Brigham Young University. Dept. of Mathematics, 2006. / Includes bibliographical references (p. 48).

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 63-66). Also available via the Internet.

Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: John D. Morgan, Dept. of Physics & Astronomy. Includes bibliographical references.

The radiative annihilation of K⁻p atoms to Λγ and ∑°γ is investigated using a non-relativistic harmonic oscillator quark model. A nonrelativistic reduction of the first order Feynman diagrams is performed to yield a gauge invariant interaction, which is sandwiched between three quark wave functions. Pseudoscalar and pseudovector coupling schemes are used for the strong vertex and the effects of SU(3)flavour breaking is explored. We obtain results which are in agreement with experiment for the ∑°γ but are somewhat high for the Λγ calculation. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Assembly of neuronal networks with distinct patterns of connectivity during nervous system development involves the growth, extension and branching of axons and dendrites. Over the years genetic and biochemical studies in model organisms have contributed significantly in identifying mechanisms regulating axon growth and extension. However the molecular mechanisms underlying axon branching remain unclear. The egg-laying neuronal circuitry in C. elegans has proven to be a robust system for identifying and characterizing novel genes involved in neuronal morphology. This circuitry which mediates egg-laying behavior in nematodes is composed of two families of motorneurons, HSNs and VCs, which are among the most branched neurons in C. elegans. A genetic screen for axon branch defects in the egg-laying neurons identified png-1 to disrupt neuronal morphology including axon branching. png-1 encodes a Peptide: N-glycanase (PNGase), a conserved cytosolic enzyme that removes N-linked sugar moieties from glycoproteins. In this thesis I present my work characterizing and examining png-1 and its role in mediating axon branching. Mutations in png-1 resulted in excessive ectopic axon branching in the VC4 and VC5 egg-laying neurons as well as branching in the normally unbranched AVL and DVB neurons. Behavioral analysis in these mutants revealed defects in egg-laying behavior and mild in-utero egg retention phenotypes. Cellular characterization shows ubiquitous expression of png-1 in many tissues including vulva cells, muscles, gonads, and neurons. My analysis also shows that png-1 acts both cell-autonomously and cell non-autonomously from neurons and epithelial cells to restrict axon branching around the vulva. Using a candidate gene approach I identified a deletion allele of the DNA repair gene, rad-23, to display axon branching defects and interact with png-1 within a common pathway to regulate axon branching. Additionally, through a genetic modifier screen for enhancers and suppressors of VC4-5 branching defects in png-1, I identified a new allele of sax-2 as an enhancer mutation. sax-2 encodes a scaffolding protein that regulates the activity and localization of sax-1, an NDR kinase. Examination of neuronal phenotypes in sax-1 and sax-2 mutants revealed similar png-1 like defects in VC4-5. Genetic analysis of the double mutants png-1;sax-1 and png-1;sax-2 revealed strong synergistic phenotypes suggesting that png-1 and sax-1/sax-2 function in parallel pathways to regulate axon branching. In summary, this thesis reveals novel components and pathways in the regulation of neuronal branching.

No description available.

No description available.

Hyphal organisms are a commonly used model system for studies of polarised growth. While growing hyphal tips offer a good example of polarised growth, little detail of the process of polarisation can be determined from them. Hyphal branching offers a good example of the development of polarity, however to date it has been largely impractical to study hyphal branching, due to the irregular timing and location along the hypha of natural branch formation. Chemical induction of branches circumnavigates this problem, using a localised concentration of nutrients adjacent to the growing hypha to stimulate controlled branching. Using previous studies of hyphal branching combined with the current understanding of hyphal tip growth, a model of the branching process was established (Jackson et al. 2001). Reception of a branching cue leads to the formation of a radial F-actin array at the new branch site. This, by means of either delivery of cell wall softening enzymes or direct mechanical pressure, leads in turn to the emergence of a visible bump in the hyphal wall. This bump enlarges and then progresses into the branch proper. The bump stage of the branching process is perhaps the least understood, with existing studies giving detail of pre- and post-bump events. The research described in this thesis suggests that bump emergence is a two stage process; an early bump stage, where localised cell wall softening leads to turgor pressure in the cell pushing out the bump, and a late bump, where F-actin is arranged into the developing branch. The addition of an F-actin inhibitor to the induction solution confirmed that the early bump stage is relatively independent of the F-actin cytoskeleton, however this experiment was unable to test F-actin's role in full branch development.

No description available.

No description available.