TRANSFORMATION OF EXTERNAL SENSILLA TO CHORDOTONAL SENSILLA IN THE CUT MUTANT OF DROSOPHILA ASSESSED BY SINGLE-CELL MARKING IN THE EMBRYO AND LARVA

The cut gene of Drosophila melanogaster is an identity selector gene t hat establishes the program of development and differentiation of exte rnal sense organs. Mutations in the cut gene cause a transformation of the external sense organs into chordotonal organs, originally assesse d by the use of immunostaining methods [Bodmer et al. (1987): Cell, 51 :293-307]. Because of evidence that axonal projections of the transfor med neurons within the central nervous system are not completely switc hed in cut mutants, the transformation of the four cells making up a s ense organ was reassessed using single-cell staining with fluorescent dye and differential interface contrast (DIC) microscopy of the embryo and larva. The results provide strong evidence that all cells of the sense organs are completely transformed, exhibiting the morphologies a nd organelles characteristic of chordotonal sense organs. A comparison of the structures of external sense organs and chordotonal organs ind icates that a number of the differences could be due to the degree of development of common structures, and that cut or downstream genes mod ulate effector genes that are normally utilized in both receptor types . The possible derivation of insect chordotonal and external sense org ans from a receptor type found in crustaceans is discussed in the ligh t of arthropod phylogenetics and the molecular genetics of sense organ development. (C) 1997 Wiley-Liss, Inc.