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 polarity 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 transduction process between the germline oocyte and the somatic follicle cells, during which the egg chamber acquires a dorsoventral polarity. K10 has been cloned and was shown to encode a putative transcription factor specifically acting in the oocyte nucleus. In order to characterize further the function of K10, we have analyzed its genetic interactions with grk, top and cni. We show that grk behaves as a dominant partial suppressor of K10. Analysis of the rescuing process of the K10 phenotype by grk shows that: (1) K10 is not indispensable for the establishment of dorsoventral polarity of the egg chamber, since its lack of function can be compensated for by reducing the grk wild-type copy number; (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 results are compatible with a model in which grk is a dorsalizing signal emanating from the oocyte nucleus, whose level of expression is regulated negatively by the K10 product.