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The developing distal cranial sensory ganglia of the chick present an interesting and tractable model for the study of general processes of neural development. While the early stages of placodal neurogenesis, including induction of the placodes and initiation of the neurogenic programme, have been extensively studied, little is known about the molecular mechanisms that regulate migration of placode-derived neuroblasts and their aggregation to form ganglia. These questions have been addressed in the context of the trigeminal ganglion, however it remains unclear whether these principles apply to the epibranchial ganglia, on which the work presented here is focussed. Molecules potentially involved in controlling placodal neuroblast migration in the epibranchial ganglia were identified through a comparative microarray screen carried out in the Begbie lab. A list of candidate genes implicated in a variety of different cellular was validated by determining expression patterns in the region of the epibranchial CSG by in situ hybridisation. These expression patterns showed that different genes were expressed by different populations within the migratory stream. This question was further addressed through the detailed analysis of the expression patterns of a panel of neuronal and neurogenic markers, leading to the finding that placodal neuroblasts appear to sequentially upregulate different groups of genes as they migrate away from the placode. Neuroblasts within the migratory stream can further be subdivided according to cell morphology, which was assessed through high resolution imaging of GFP-labelled placodal cells. Multipolar and bipolar cells were concentrated around two different regions of the migratory stream with multipolar cells localised near the placode and bipolar cells localised closer to the neural tube. Together these findings support the hypothesis that placodal neuroblasts mature as they migrate towards the site of ganglion aggregation. With this detailed description of the system in mind, the question of molecular control was addressed through the functional characterisation of a candidate gene identified in the original microarray screen. MDGA1, a GPI-anchored IgSF molecule that has been implicated in controlling radial migration of cortical neurons, was specifically expressed in the chick CSG at the relevant stages. RNAi-mediated knockdown and overexpression were used to test the function of MDGA1 in migrating placodal neuroblasts. These experiments showed that MDGA1 negatively regulates the formation and extension of neuronal projections in bipolar neuroblasts. With the mechanisms of MDGA1 function relying entirely on protein-protein interactions at the cell-surface, we then set out to identify and characterise potential MDGA1 binding partners. SPR binding experiments carried out in collaboration with the Aricescu lab revealed that MDGA1 interacts with the Neuroligin family of synaptic proteins. Recent evidence has shown that MDGA1 interacts in cis with NLGN2 in rat hippocampal neurons where it disrupts its interaction in trans with Neurexin1. Neuroligins and Neurexins function to stabilise dendritic filopodia by creating trans-synaptic adhesions and recruiting the synaptic apparatus. Having determined that both NLGN2 and NRXN1 are expressed in placode-derived neuroblasts of the CSG, we propose that these molecules play a role in the stabilisation and extension of neuronal projections in this system and that this function in modulated by MDGA1 function.

Call number: LD2668 .T4 1958 B57 / Master of Science

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2015. / Claudins are a family of proteins that are conserved amongst all vertebrates, they are integral in the formation and maintenance of the tight junctions between epithelial cells. Claudins are implicated in embryo morphogenesis, vertebrate evolution, solute movement, cell-cell adhesion, designation of cellular and tissue identity, and several diseases when mutated. Petromyzon marinus (the sea lamprey) is the most basal extant vertebrate and is a model organism in both developmental and evolutionary biology for this reason. In this study, the expression patterns and functions of novel claudin genes in P. marinus were examined with the aim of discovering more about the role of claudins in vertebrate evolution. Presumptive claudin genes in P. marinus were compared to all known claudins in the NCBI database. Primers were designed against all known P. marinus claudin genes and RT-PCR was performed in order to determine their expression levels at embryonic stages E8 to E18, as well as in adult eye, gill, heart, liver and skin tissues. Probes were designed against Claudin 1a, Claudin 9, Claudin 10 and Claudin 19b and RNA in situ hybridisation was performed on embryos at developmental stages E4 to E31 in order to determine their spatial expression patterns. Areas of common claudin gene expression appear to include the pharyngeal arches, otic placode, neural tube, notochord and ectoderm. Claudin 1a is uniquely expressed in the lamprey migrating neural crest. Morpholino-mediated gene knockouts were performed on P. marinus embryos and the loss of Claudin 19b appears to result in abnormal somite morphogenesis.

University of Macau / Faculty of Science and Technology. / Department of Electromechanical Engineering

Zhang, Yafeng. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 53-64). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Gata4 and Gata6 are closely related transcription factors that are essential for the development of a number of embryonic tissues. While they have nearly identical DNA-binding domains and similar patterns of expression, Gata4 and Gata6 null embryos have strikingly different embryonic lethal phenotypes. Conditional deletion of these genes in the pancreas has also revealed specific functions for each factor in this organ. To investigate the role of these genes in pancreatic development, we performed a number of biochemical experiments on pancreatic cell lines and mutant tissues. We found that Gata4 and Gata6 regulate overlapping sets of genes in the developing pancreas. To determine whether the lack of global redundancy between Gata4 and Gata6 is due to differences in protein function or Gata4 and Gata6 expression domains, we generated mice that contained the Gata6 cDNA in place of the Gata4 genomic locus. Gata4Gata6/Gata6 embryos survived through embryonic day (e)12.5 and successfully underwent ventral folding morphogenesis, demonstrating that Gata6 is able to replace Gata4 function in extraembryonic tissues. Interestingly, Gata6 is unable to replace Gata4 function in the septum transversum mesenchyme or the epicardium, leading to liver agenesis and lethal heart defects in Gata4Gata6/Gata6 embryos. These studies suggest that Gata4 has evolved distinct functions in the development of these tissues that cannot be performed by Gata6, even when it is provided in the identical expression domain. Our work has important implications for the respective mechanisms of Gata function during development, as well as the functional evolution of these essential transcription factors.

As nutrition is of central importance to cattle fertility, this study sought to assess how veterinarians and nutritional advisers manage trace element imbalance in the UK; diagnosis and treatment. The study also sought to develop a robust system for oocyte recovery (ovum pick-up (OPU)) and in vitro embryo production (IVP) for commercial use, and to identify key factors influencing success, including oestrus synchrony and ovarian stimulation prior to OPU. The intention originally was to use OPU/IVP to investigate the impact of mineral imbalances on bovine oocyte quality, early embryo development and pregnancy establishment following embryo transfer (ET). In the first survey of its kind in the UK, the understanding and approach of advisers to mineral nutrition on farms was investigated. Of the 173 respondents, 78% were vets in practice. The overall importance of minerals was recorded by vets as low 33%, medium 37%, and high 30%, while non-vets scored importance as low 17%, medium 48%, and high 35%. There was little consensus amongst the advisers, or within the vet and non-vet subgroups about mechanisms and interactions associated with deficiency, and particularly of copper responsive conditions. The most frequently identified deficiencies were selenium, copper and iodine, while the most commonly identified toxicity was molybdenum. For copper responsive conditions, all of the listed treatments were used at least "occasionally"; the most frequently being glass boluses, in-feed supplementation, matrix boluses, and then copper injections. While there was a diverse choice of treatments, altering the ration was relatively rarely selected. This thesis also provides the first large-scale retrospective analysis of factors influencing the establishment of a commercially robust ovum pick up (OPU) and in vitro embryo production (IVP) platform in the UK. Over a 5-year period, a system was developed and validated for use in the UK with 2,138 cycles of OPU. These cycles were analysed as four sets of data and included two IVP laboratories and 6 OPU teams. Factors in these analyses included OPU team, IVP laboratory, ovarian stimulation protocol and semen type (unsorted vs sex-sorted). The mean number of follicles aspirated by the OPU teams ranged from 6.5 to 14.9 (P < 0.001), while the number of oocytes collected was between 4.0 and 12.4 (P < 0.001). There was an indication (P=0.055) that the blastocyst per oocyte rate varied between teams. The proportion of blastocysts from oocytes that cleaved was higher (P=0.01) for unsorted than sexed semen. Two commercial products containing different ratios of follicle stimulating hormone (FSH) to luteinising hormone (LH) (Folltropin® and Pluset®) were compared in ovarian stimulation programs. The addition of 'coasting' (short-term (typically 48h) hormonal withdrawal after FSH stimulation), prior to OPU was also investigated. Pluset® resulted in a greater (P < 0.001) mean number of follicles aspirated, more (P=0.003) blastocysts per oocyte matured and more (P < 0.001) embryos per cycle (2.45), compared with Folltropin® (1.17) or with no stimulation (1.24). Throughout the study there was a steady improvement in blastocyst production per OPU cycle. In a separate analysis, Grade 1 cumulus oocyte complexes (COCs) as a proportion of COCs recovered, oocytes that cleaved as a proportion of total COCs, and blastocysts as a proportion of total COCs, were all greater (P < 0.05) for stimulated than non-stimulated cycles, irrespective of FSH/LH product. A composite score of oocyte quality and quantity was proposed (sCOC); Log Total Mean sCOC was correlated (P < 0.001) with both the proportion of blastocysts per oocyte collected, and the total number of embryos produced per cycle. Finally, twelve peri-pubertal heifers (approximately 10 months old) participated in a crossover trial which compared PRID® (Delta®) vs CIDR® progesterone releasing intravaginal devices for use in OPU/IVP cycles. Vaginoscopic examination found higher vaginal inflammation grades for PRID® than CIDR® (P < 0.001). There was evidence of vaginal inflammation continuing for at least 2 weeks after device withdrawal. The proportion cleaved of oocytes inseminated was higher for PRID® than CIDR® (P < 0.05). Numerically but not significantly there was a higher proportion of blastocysts per cycle and a higher Log Total Mean sCOC score per cycle with PRID® than CIDR® treatments, but blastocyst yield was low throughout, suggesting a need to repeat the trial. Data collection and analyses are ongoing, to identify other key performance indicators within the OPU/IVP embryo transfer (ET) system, with a view to refining the sCOC composite score model. A robust OPU/IVP/ET system has been developed and this could be used to investigate further how mineral imbalances impact oocyte competence and blastocyst yield.

Bibliography: leaves 202-238. Gives an overall understanding of embryonic development of Heterodontus portusjacksoni.