The polarisation of the anterior-posterior and dorsal-ventral axes during Drosophila oogenesis

Recent work on Drosophila oogenesis has begun to reveal how the first asymm etries in development arise and how these relate to the later events that l ocalise the positional cues which define the embryonic axes. The Cadherin-d ependent positioning of the oocyte creates an anterior-posterior polarity t hat is transmitted to the embryo through the localisation and localised tra nslation of bicoid, oskar, and nanos mRNA. In contrast, dorsal-ventral pola rity arises from the random migration of the nucleus to the anterior of the oocyte, where it determines where gurken mRNA is translated and localised. Gurken signalling then defines the embryonic dorsal-ventral axis by restri cting pipe expression to the ventral follicle cells, where Pipe regulates t he production of an unidentified cue that activates the Toll signalling pat hway.