SPECIFICATION OF NEUROBLAST IDENTITY IN THE DROSOPHILA EMBRYONIC CENTRAL-NERVOUS-SYSTEM BY GOOSEBERRY-DISTAL

THE Drosophila central nervous system develops from a segmentally reit erated array of 30 unique neural precursors, called neuroblasts. Each neuroblast goes through a stereotyped cell lineage to produce an invar iant clone of neural progeny. It is critical to identify the genes tha t specify neuroblast identity as these genes control the time of forma tion, gene expression profile, and cell lineage characteristics of eac h neuroblast. Here we show that the Pax-type gooseberry-distal gene sp ecifies row 5 neuroblast identity. Initially, four rows of neuroblasts form per segment (1, 3, 5, 7) and gooseberry-distal is expressed in r ow 5 neuroblasts(1-3). By using 10 molecular markers, and by following the number and orientation of neuroblast divisions, we show that lack of gooseberry-distal transforms row 5 neuroblasts into row 3 neurobla sts, whereas ubiquitous gooseberry-distal generates the reciprocal tra nsformation. Thus, gooseberry-distal is necessary and sufficient to sp ecify row 5 neuroblast identity autonomously, The 10 genes coordinatel y regulated by gooseberry-distal are prime candidates for controlling specific aspects of neuroblast identity.