Diversification of cell types in the Drosophila eye by differential expression of prepattern genes

According to Freeman (Development, 124 (1997) 261), reiterative use of Spit z signals emanating from already differentiated ommatidial cells triggers t he differentiation of around ten different types of cells. Here we show evi dence that the choice of cell fate by newly recruited ommatidial cells stri ctly depends on their developmental potential. Using forced expression of a constitutively active form of Ras1, three developmental potentials (rough, seven-up, and prospero expression) were visualized as relatively narrow ba nds corresponding to regions where rough-, seven-up- or prospero-expressing ommatidial cells would normally form. Ras1-dependent expression of ommatid ial marker genes was regulated by a combinatorial expression of eye prepatt ern genes such as lozenge, dachshund, eyes absent, and cubitus interruptus, indicating that developmental potential formation is governed by region-sp ecific prepattern gene expression. (C) 2001 Elsevier Science Ireland Ltd. A ll rights reserved.