DORSOVENTRAL AXIS FORMATION IN DROSOPHILA DEPENDS ON THE CORRECT DOSAGE OF THE GENE GURKEN

The Drosophila gene gurken participates in a signaling process that oc curs between the germ line and the somatic cells (follicle cells) of t he ovary. This process is required for correct patterning of the dorso ventral axis of both the egg and the embryo. gurken produces a spatial ly localized transcript which encodes a TGF-alpha-like molecule (Neuma n-Silberberg and Schupbach, Cell 75, 165-174,1993). Mutations in gurke n cause a ventralized phenotype in egg and embryo. To determine whethe r the gurken gene product plays an instructive role in dorsoventral pa tterning, we constructed females containing extra copies of a gurken t ransgene. Such females produce dorsalized eggs and embryos, which is e xpected if gurken acts as a limiting factor in the dorsoventral patter ning process. In addition, the expression pattern of the gene rhomboid in the follicle cells is altered in ovaries of females containing ext ra copies of gurken. Our results indicate that changing gurken dosage in otherwise wild-type ovaries is sufficient to alter the number of so matic follicle cells directed to the dorsal fate. Therefore the gurken -torpedo signaling process plays an instructive role in oogenesis. It induces dorsal cell fates in the follicle cell epithelium and it contr ols the production of maternal components that will direct the embryon ic dorsoventral pattern after fertilization.