Morphological Search for Evidence of Neuron Precurser Cells in the Embryonic Optic Stalk
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Juurlink and Fedoroff (1979) found that ventricular cells of the optic stalks of mice have the potential to form both neruons and macroglial cells. They cultured optic stalks from mouse embryos at Theiler stages 16-23, which were removed from their normal in situ environments. The optic stalks they obtained from embryos at stages 16-19 (10-11.5 days of gestation) gave rise to both neuron and macroglial precursor cells, while between stages 20-23 (12-15 days of gestation) only macroglial cells developed. An event occurred during this 12 hour period which restricted capabilities of the ventricular cells. This restriction could be due to a limitation of multipotential cells or to a selective cell death of a population of ventricular cells predisposed to become neurons. The purpose of the present study was to look for additional evidence which either supported or contradicted Juurlink and Fedoroff's claim that the ventricular cells of the optic stalk have the potential to generate neurons. It was also hoped to determine if the optic stalk gives rise to two separate cell lineages or to multipotential cells. This study also tested the hypothesis proposed by Juurlink and Fedoroff (1979) that environmental cues such as retinal axon growth caused the restriction of the optic stalk ventricular cells. Light micrographs of serial sections of optic stalks at 13 days of gestation (13e) showed numerous dead cells. This cell death supported the theory of a separate cell line in the embryonic optic stalk predisposed to become neurons, rather than the "turninq off" of a multipotential line of cells. Finding cell death before 13 days of gestation conflicted with the hypothesis suggested by Juurlink and Fedoroff (1979). Contrary to their hypothesis the growth of retinal axons could not be responsible for the restriction of the differentiation of neurons in the optic stalk, because the axons did not extend into the optic stalk until 14 days of gestation.