A REGULATORY FUNCTION FOR K10 IN THE ESTABLISHMENT OF DORSOVENTRAL POLARITY IN THE DROSOPHILA EGG AND EMBRYO

Several lines of evidence suggest that the origin of pattern formation of Drosophila embryos must be traced back to oogenesis, to the polari ty of the egg chamber. A few early-acting genes, K10, top, grk and cni , have been identified which are assumed to function in a signal trans duction process between the germline oocyte and the somatic follicle c ells, during which the egg chamber acquires a dorsovental polarity. K1 0 has been cloned and was shown to encode a putative transcription fac tor specifically acting in the oocyte nucleus. In order to characteriz e further the function of K10, we have analyzed its genetic interactio ns with grk, top and cni. We show that grk behaves as a dominant parti al suppressor of K10. Analysis of the rescuing process of the K10 phen otype by grk shows that: (1) K10 is not indispensable for the establis hment of dorsoventral polarity of the egg chamber, since its lack of f unction can be compensated for by reducing the grk wild-type copy numb er; (2) grk function is highly dose-sensitive; (3) the rescue process shows an anteroposterior effect suggesting that K10 may also interact with genes involved in anteroposterior pattern formation. These result s are compatible with a model in which grk is a dorsalizing signal ema nating from the oocyte nucleus, whose level of expression is regulated negatively by the K10 product.