fringe and Notch specify polar cell fate during Drosophila oogenesis

Fringe encodes a glycosyltransferase that modulates the ability of the Notc h receptor to be activated by its ligands. We describe studies of fringe fu nction during early stages of Drosophila oogenesis. Animals mutant for hypo morphic alleles of fringe contain follicles with an incorrect number of ger mline cells, which are separated by abnormally long and disorganized stalks . Analysis of clones of somatic cells mutant for a null allele of fringe lo calizes the requirement for fringed in follicle formation to the polar cell s, and demonstrates that fringe is required for polar cell fate. Clones of cells mutant for Notch also lack polar cells and the requirement for Notch in follicle formation appears to map to the polar cells. Ectopic expression of fringe or of an activated form of Notch can generate an extra polar cel l. Our results indicate that fringe plays a key role in positioning Notch a ctivation during early oogenesis, and establish a function for the polar ce lls in separating germline cysts into individual follicles.