Expression of fringe is down regulated by Gurken/Epidermal Growth Factor Receptor signalling and is required for the morphogenesis of ovarian follicle cells

Signalling by the Gurken/Epidermal Growth Factor Receptor (Grk/EGFR) pathwa y is involved in epithelial cell fate decision, morphogenesis and axis esta blishment in Drosophila oogenesis. In the search for genes downstream of th e Grk/EGFR signal transduction pathway (STP), we isolated a number of genes that are components of other STPs. One of them is a known gene, called fri nge (fng), Drosophila fng encodes a putative secreted protein that is requi red at other development stages for mediating interactions between dorsal a nd ventral cells via Notch signalling. Here we show that fng has a dynamic expression pattern in oogenesis and that its expression in specific groups of follicle cells along the anterior-posterior and dorsal-ventral axes is d efined by the repression of fng by Grk, Interfering with fng expression usi ng antisense RNA experiments resulted in a typical fng mutant phenotype in the wing, and malformed egg chambers and abnormal organisation of the folli cle cells in the ovaries, revealing that fng is essential in oogenesis for the proper formation of the egg chamber and for epithelial morphogenesis. T his has been confirmed by re-examination of fng mutants and analysis of fng mutant clones in oogenesis.