EXPRESSION OF THE DROSOPHILA-OPTOMOTOR-BLIND GENE TRANSCRIPT IN NEURONAL AND GLIAL-CELLS OF THE DEVELOPING NERVOUS-SYSTEM

Mutations in the complex gene locus optomotor-blind (omb) can lead to defects in the development of both the optic lobes and external featur es of the adult fly. We describe here the expression of omb in the dev eloping and adult nervous system using in situ hybridization. During e mbryogenesis, omb expression is first observed in the optic lobe anlag en. It later expands to a larger part of the developing larval brain a nd to the gnathal lobes. Cells in the ventral and peripheral nervous s ystems begin to express omb after completion of germ band extension. L ater in embryonic development, expression declines and only persists i n the antenno-maxillary complex and in part of the brain hemispheres. During the larval and pupal stages, omb expression in the brain is con fined to the developing optic lobes and contiguous regions of the cent ral brain. At these stages, only a few cells show expression in the ve ntral ganglion. In the eye imaginal disc, transcript accumulation is m ost conspicuous in a group of presumptive glia precursor cells posteri or to the morphogenetic furrow and in the optic stalk. In the adult br ain, expression is prominent in several regions of the optic lobe cort ex and along the border between central brain and optic lobes. In the mutation In(1)omb(H31), 40 kb of regulatory DNA, downstream from the t ranscription unit, are removed from the omb gene. In(1)omb(H31) is cha racterized by the lack of a set of giant interneurons from the lobula plate of the adult optic lobes. We find that, already during embryogen esis, there is a drastic difference between wild type and In(1)omb(H31 ) in the level of the omb transcript in the optic lobe primordia. The adult mutant phenotype may thus be caused by omb misexpression during embryonic development.