hold up is required for establishment of oocyte positioning, follicle cell fate and egg polarity and cooperates with Egfr during Drosophila oogenesis.

In Drosophila the posterior positioning of the oocyte within the germline cluster defines the initial asymmetry during oogenesis. From this early event, specification of both body axes is controlled through reciprocal signaling between germline and soma. Here it is shown that the mutation hold up (hup) affects oocyte positioning in the egg chamber, follicle cell fate and localization of different markers in the growing oocytes. This occurs not only in dicephalic egg chambers, but also in oocytes normally located at the posterior. Generation of mosaic egg chambers indicates that hup has to be at least somatically required. Possible interactions of hup with Egfr, the Drosophila epidermal growth factor receptor homolog, have been investigated in homozygous double mutants constructed by recombination. Stronger new ovarian phenotypes have been obtained, the most striking being accumulation of follicle cells in multiple layers posteriorly to the oocyte. It is proposed that the hup gene product is a component of the molecular machinery that leads to the establishment of polarity both in follicle cell layer and oocyte, acting in the same or in a parallel pathway of Egfr.