Genesis of the adult retina and outer optic lobes of the moth,Manduca sexta. I. Patterns of proliferation and cell death

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Abstract
We have examined the development of the adult retina and the outer optic lobes in the moth Manduca sexta. The adult retina is generated from a group of epithelial cells lying within the larval head capsule between the larval ocelli and antenna. Proliferation of these cells begins during the feeding larval stage but accelerates at the end of the final larval instar. Proliferation occurs in two zones of mitotic activity; these zones flank a furrow in the presumptive retinal epithelium. The furrow and flanking mitotic zones migrate from posterior to anterior across the presumptive retinal epithelium. Posterior to the furrow, presumptive retinal cells form clusters and extend axons into the larval optic nerve. We have also examined the temporal patterns of neuronal proliferation and cell death during genesis of the adult outer optic ganglia, the medulla and the lamina. The medulla and the lamina are generated by distinct populations of neuroblasts in the outer optic anlage; the neuroblasts divide asymmetrically to generate ganglion mother cells. Ganglion mother cells later divide symmetrically to generate immature neurons. Generation of the medulla cortex starts with the onset of the final larval instar, and cell death within the medulla cortex begins after the end of the final larval instar. Generation of the lamina cortex is initiated with the arrival of retinal afferents at the optic lobes, and cell death in the lamina cortex begins 1 day later. Generation of the outer optic ganglia terminates with the abrupt cessation of mitotic activity followed by degeneration of the outer optic anlage.