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No description available.

No description available.

No description available.

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.

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Two tropical legumes and a temperate legume were studied during the course of this work. These were Leucaena leucocephala (cv. Peru), Canavalia ensiformis(cv. unknown) and Lupinus albus (cv. Vladimir [Kievskji mutant]) respectively. The dried ground leaf obtained from Leucaena leucocephala (LLM), the seeds of Canavalia ensiformis (jack bean; JB) and Lupinus albus (lupin) were the materials used in the study. Liquid chromatographic methods (HPLC) were developed for the analysis of mimosine and 3-hydroxy-4(lH )-pyridone (3,4-DHP) in LLM, Leucaena seed (LS) and chick excreta. Neither mimosine nor 3,4-DHP wftS detected in the serum of chicks fed LLM. Poor and variable recoveries of mimosine and 3,4-DHP were obtained when these were added to serum The analysis of canavanine in JB and the serum of chicks fed JB and canavanine, was also accomplished using HPLC. Canaline was not detected in any of the samples analysed by HPLC although recovery of added canaline to serum, JB and excreta was high. A small amount of what appeared to be canavanine was detected in lupin. Saponins and tannins were found in all the legumes under study. Trypsin inhibitors were detected in all but the lupins Inclusion of LLM in chick diets reduced their performance. Addition of Fe(III), polyethylene glycol (RAM = 4000) and cholesterol to LLM diets improved chick performance almost to that of chicks fed control diets. Cooking LLM alsoimproved chick performance. Addition of enzymes to LLM did not improvechick performance and did not improve the apparent metabolisable energy (AME) of LLM. Dietary inclusion of mimosine or LS, to supply the same amount of mimosine as that from LLM, did not restrict chick performance to the same extent as LLM Inclusion of autoclaved jack bean (JB) in chick diets caused a severe reduction in chick performance. The reduction in performance was not matched byinclusion of canavanine at the same level as that from JB. The inclusion ofextracted JB also reduced chick performance. Germination of the JB, prior to autoclaving and dietary inclusion, did not reduce canavanine levels nor was chick performance improved. Addition of arginine to JB diets improved performance of chicks but additional lysine had no beneficial effect. Lupin diets perm itted chicks to perform much better than LLM or JB diets. Autoclaving made little difference to the AME of lupins although the results were probably confounded by the presence of M aillard reaction products. Addition of enzymes to lupins increased the concentration of lower molecular weight carbohydrates but only had a small beneficial effect on AME of lupins for chicks.

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No description available.

No description available.