DEVELOPING COMPOUND EYE IN LOZENGE MUTANTS OF DROSOPHILA - LOZENGE EXPRESSION IN THE R7 EQUIVALENCE GROUP

The lozenge locus is genetically complex, containing two functionally distinct units, cistrons A and B, that influence the structure of the compound eye. Extreme mutations of either cistron produce adult phenot ypes that share similarities and that have striking differences. We ha ve analyzed the expression of several developmentally important eye ge nes including boss, scabrous, rhomboid, seven-up, and Bar in lozenge m utant backgrounds representing both cistrons. This analysis follows th e progressive recruitment of photoreceptor neurons during eye developm ent and has confirmed that the initial development of photoreceptors i s normal up to the five cell precluster stage (R8, R2/5 and R3/4). How ever, when lozenge is mutant, further eye development is perturbed. As cells R1, R6 and R7 are recruited, patterns of gene expression for se ven-up, and Bar become abnormal. We have also characterized the expres sion of two different enhancer trap alleles of lozenge. The lozenge pr oduct(s) appear to be first expressed in the eye disc in undifferentia ted cells shortly after the five cell precluster forms. Then, as disti nct cells are recruited to a fate, lozenge expression persists and is refined in those cells. Our data suggests that lozenge functions in co ne cells and pigment cells as well as in specific glia. With respect t o photoreceptor neurons, lozenge biases the developmental potential of cells R1, R6 and R7, by directly influencing the expression of genes important for establishing cell fate.