DOWN-REGULATION OF TRANSCRIPTION FACTOR CF2 BY DROSOPHILA RAS MAP KINASE SIGNALING IN OOGENESIS - CYTOPLASMIC RETENTION AND DEGRADATION/

Dorsoventral (D/V) patterning in Drosophila oogenesis is initiated by the transmission of a TGF-cu-like ligand, Gurken (Grk), from the oocyt e to the anterodorsal follicle cells, activating the EGF receptor (Egf r) signaling pathway. The zinc-finger transcription faster CF2 is a ne gative regulator of the rhomboid (rho) gene that encodes an essential membrane-bound component of the dorsalizing pathway, Expression of CF2 itself is negatively regulated by the activated Egfr, In this report, we demonstrate that CF2 is the target of down-regulation by the MAPK kinase cascade, and that this down-regulation is independent of the Wh o function. These results suggest that D/V patterning involves a two-s tep signaling process: the initial Egfr signal, which represses CF2 an d induces rho expression; and the subsequent Egfr + Who signal, which determines the dorsal cell fates. Furthermore, we show that CF2 down-r egulation occurs at the post-translational level through a mechanism i nvolving coupled cytoplasmic retention and degradation.