Structural brain mutant of Drosophila melanogaster with reduced cell number in the medulla cortex and with normal optomotor yaw response

Abstract

KS58, 1 out of 6 known alleles of the small optic lobes (sol) gene in D. melanogaster, reduces the cell number in the medulla cortex by degeneration of ganglion cells in the pupae to about 50%. About half the volume of the medulla and lobula complex neuropils is missing. Many Golgi-stained cells in the mutant optic lobes resemble their homologs in wild type. Special classes of transmedullary columnar neurons projecting to the lobula or to both lobula and lobula plate are not seen in the mutant. Some neurons linking the lobula complex to the central brain send branches to the medulla (the branches do not exist in wild type); some other types seem to be missing. The fate mapping of the KS58 focus reveals a location ventral to the head bristles and in sine oculis (so) flies the mutation further reduces the rudiments of the optic lobes normally seen. The sol phenotype is not induced by mutant eyes and the primary gene action seems to be on nervous tissue. The structural alterations of the small optic lobes are reflected in visual orientation behavior. The optomotor yaw response is almost quantitatively preserved. The respective neural network should still be present in the mutant optic lobes.