DEVELOPMENT OF THE DROSOPHILA OLFACTORY SENSE-ORGANS UTILIZES CELL-CELL INTERACTIONS AS WELL AS LINEAGE

We have examined the mechanisms underlying the development of the olfa ctory sense organs on the third segment of the antenna of Drosophila. Our studies suggest that a novel developmental strategy is employed. S pecification of the founder or precursor cell is not governed by the g enes of the achaete-scute complex. Another basic helix-loop-helix enco ding gene, atonal, is essential for determination of only a subset of the sensilla types - the sensilla coel-oconica. Therefore, we predict the existence of additional proneural genes for the selection of sensi lla trichoidea and sensilla basiconica. The choice of a founder cell f rom the presumed proneural domain is regulated by Notch activity. Soon after delamination of the founder cell, two to three additional neigh boring cells also take on a sensory fate and these cells together form a presensillum cluster. The selection of neighbors does not occur whe n endocytosis is blocked using a temperature sensitive allele of shibi re, thus suggesting that cell-cell communication is required for this step. The cells of the cluster divide once before terminal differentia tion which is influenced by Notch activity. The final cell number with in each sensillum is controlled by programmed cell death.