LBH is a highly conserved protein whose role during vertebrate development is relatively under-studied. In collaboration with the Albertson lab, our lab has previously shown that it is necessary for cranial neural crest cell migration in the zebrafish and in Xenopus laevis. The molecular mechanisms through which it acts are not well understood. In Xenopus, LBH is a maternally deposited protein. As such, studying its role in early development has not been feasible through the morpholino-mediated knockdown techniques that prevent translation of target genes. Recently, a technique for degrading endogenous proteins was developed, called Trim-Away. This was developed in mammalian systems and utilizes the E3 ubiquitin ligase Trim21 in conjunction with an antibody against a protein of interest in order to degrade the protein. In order to observe the effects of a knockdown of LBH during early embryonic development, we sought to modify the technique for use in Xenopus. We injected embryos with mRNA encoding the human form of trim21 along with a monoclonal antibody against LBH that our lab developed (2B8) and tracked degradation of the protein over time, monitoring embryos for any phenotypes arising during early development. Our results demonstrate that Trim-Away can be utilized in Xenopus. LBH depleted embryos display a variety of defects during gastrulation, the process by which the three germ layers are properly organized. These appear to be mainly due to defects in fibronectin fibrillogenesis and mesodermal migration.

Ultraviolet (UV) spectra obtained from Earth’s dayglow contain important information for understanding the thermosphere, and the N2 Lyman-Birge-Hopfield (LBH) bands are possibly the most useful emission. To be useful, a thorough understanding of how the LBH band emission varies with altitude and latitude is essential to present and future use of this emission by space-based remote sensors. Excited by photoelectron impact on N2 leading to transitions from the a 1Πg state to the ground state, the LBH emissions radiate between 1270 and 2400 Å. In addition to being populated by electron impact excitation, the a 1Πg state is populated by radiative and collisional cascading from adjacent singlet states a’ 1Σ−u, and w 1∆u (Eastes, 2000). Ultimately, the intensity is most dependent on low energy electron flux (Ajello and Shemansky, 1985; Meier, 1991) because that is where the electron impact scattering cross sections of the singlet states are the largest. This dissertation presents modeled LBH profiles produced using the Intrasystem Cascade Excitation (ICE) model (Eastes, 2000) with photoelectron fluxes calculated using the Continuous Slowing Down (CSD) model (Jasperse, 1976). Both of these models implement the Mass Spectrometer and Incoherent Scatter (MSIS) to model an atmosphere. Modeled emissions are compared against observations by the High resolution Ionospheric and Thermospheric Spectrograph (HITS) on the Advanced Research and Global Observation Satellite (ARGOS). This dissertation will investigate the LBH emissions in detail and ultimately use them for remote sensing of thermospheric temperatures.

In this research study three subject didactical measuring instruments were compared with regard to certain psychometric characteristics of a group of grade nine learners in the Tzaneen and Phalaborwa region, in the Northern Province. The primary goal of this study was to optimize learning competencies with regard to subject context. The SOM-, LEMOSS(II)- and LCH-questionnaires can be applied at the start or at the end of an academic year to an individual or to a group in order to identify learners who need specific help, counseling, remediation and support in the subjects mathematics, natural and domestic sciences in order to facilitate learning. The following aspects have been handled in this study, such as: In chapter 1 an attempt is made to clarify and define the title and certain relevant concepts. The research statement and questions are formulated. The research design is briefly discussed and the primary goal and objectives are set. Other aspects that enjoy attention include the types of research that were used, the method of sampling, data gathering and analysis, as well as the progress of the study. Literature on subject didactics is discussed in chapter 2 for the conceptualising of basic related aspects by means of a macro-model for the optimising of learning competencies in the context of a specific subject. This model emphasises subject content, form and competencies that should be taken into consideration when planning a learning opportunity. Other aspects concerning learning, namely relevant theories, approaches, models, styles, strategies and motives were discussed in order to facilitate learning in mathematics, natural and domestic sciences. In chapter 3 the SOM-, LEMOSS(II)- and LCH-questionnaires as diagnostic instruments are described. The diagnostic value, background, categories and psychometric aspects of the measuring instruments are briefly discussed. In chapter 4 the method of investigation used for the comparison of the SOM- LEMOSS(II)- and LCH-instruments regarding their reliability and validity is described and it includes the goal, hypothesis and method of sampling as an extension of the research design. The way in which descriptive and inferential statistics are conveyed is theoretically described In chapter 5 the results and qualitative conclusions of the empiric-analytical investigation are included. The SOM-, LEMOSS(II)- and LCH-questionnaires are compared with regard to reliability and validity of a group grade nine learners in the Tzaneen and Phalaborwa region. Reliability is discussed by means of test-retest reliability and pared observations. Pared observations include staggering, locality and pared t- and sign-rank testing. Validity refers to criteria referenced validity with regards to simultaneous and predictable validity. Simultaneous validity is described by means of the relation between the subject mark and the field, and by stepwise and multiple regression analysis. In chapter 6 the study is concluded with the brief answering of the research questions and by describing the research findings by means of the research statement. Possible limitations are shown and recommendations for future research are made. / Dissertation (PhD)--University of Pretoria, 2001. / Humanities Education / Unrestricted