Properties and behaviour of progenitor cells in embryonic chick retina
During embryonic development, interactions between extracellular signalling molecules and intracellular transduction pathways are involved in the regulation of cell proliferation, differentiation and migration. This thesis investigates the properties and behaviour of cells in the developing neural retina of 4-9 day old chick embryos. In addition, it describes the expression of amino acid transmitter receptors and gap junctional communication amongst progenitor cells and newly differentiated neurons at these early times. The membrane properties of progenitor cells and postmitotic neurons were investigated using whole-cell patchclamping of cells in retinal slices. The results show that E5-E8 progenitor cells, but not postmitotic neurons, respond to GABA and glutamate and are coupled via gap junctions to neighbouring cells. Postmitotic neurons, but not progenitor cells, express time-dependent, voltage- gated currents. Progenitor cells are characterized by extensive gap junctional coupling, which gradually increases from E4-E6, and decreases towards the end of neurogenesis, from E7-E9. Postmitotic cells are excluded from the coupled clusters. The expression of Cx43 and Cx36 is consistent with a role for these connexin proteins in mediating the coupling between proliferating cells, and interference with Cx43 expression resulted in a reduction in gap junction coupling. The interkinetic nuclear migration and division of progenitor cells was followed in real time using confocal microscopy. The movement of these cells is saltatory, and characterized by stationary phases interspersed with rapid movements in both directions, to produce an average rate of movement of around 20um per hour. The maintenance of normal rates of migration is dependent on intact gap junctional communication. Unopposed gap junction hemichannels were found to play a role in migration. The effect of neurotransmitters on interkinetic nuclear migration was also investigated. Agonists and antagonists of GABA-, glutamate-, ACh-, and purine-receptors were found to have minor effects on interkinetic nuclear migration.