GENESIS OF THE ADULT RETINA AND OUTER OPTIC LOBES OF THE MOTH, MANDUCA-SEXTA .1. PATTERNS OF PROLIFERATION AND CELL-DEATH

We have examined the development of the adult retina and the outer opt ic lobes in the moth Manduca sexta. The adult retina is generated from a group of epithelial cells lying within the larval head capsule betw een the larval ocelli and antenna. Proliferation of these cells begins during the feeding larval stage but accelerates at the end of the fin al larval instar. Proliferation occurs in two zones of mitotic activit y; these zones flank a furrow in the presumptive retinal epithelium. T he furrow and flanking mitotic zones migrate from posterior to anterio r across the presumptive retinal epithelium. Posterior to the furrow, presumptive retinal cells form clusters and extend axons into the larv al optic nerve. We have also examined the temporal patterns of neurona l proliferation and cell death during genesis of the adult outer optic ganglia, the medulla and the lamina. The medulla and the lamina are g enerated by distinct populations of neuroblasts in the outer optic anl age; the neuroblasts divide asymmetrically to generate ganglion mother cells. Ganglion mother cells later divide symmetrically to generate i mmature neurons. Generation of the medulla cortex starts with the onse t of the final larval instar, and cell death within the medulla cortex begins after the end of the final larval instar. Generation of the la mina cortex is initiated with the arrival of retinal afferents at the optic lobes, and cell death in the lamina cortex begins 1 day later. G eneration of the outer optic ganglia terminates with the abrupt cessat ion of mitotic activity followed by degeneration of the outer optic an lage. (C) 1996 Wiley-Liss, Inc.