Follicle cells and germ line cells both affect polarity in dicephalic chimeric follicles of Drosophila.

In aberrant egg follicles of the pattern mutant dicephalic (dic) the oocyte is wedged in between two groups of nurse cells, and this condition may give rise to embryos which express anterior traits at both ends. We have analysed the role of the dic genotype of the germ line cells and the surrounding somatic follicle cells in the formation of the dic follicular phenotype. By means of pole cell transplantations into Fs (1) K 1237 hosts (this cell-autonomous mutation causes degeneration of the host's germ line cells early in oogenesis), we constructed chimeras in which either the follicle cells, the germ line cells, or both were homozygous for the dic mutation. In all three combinations the dic phenotype was expressed but not in controls with dic + in both germ line cells and follicular epithelium. Since follicles with the dic phenotype may be produced if either the germ line cells or the follicle cells lack dic + gene activity we suggest that cellular interactions between both cell types are required for the correct positioning of the oocyte at the follicle's posterior pole.