Rab11, a vesicle transport protein, is required to maintain cell polarity in the oocyte. G.L. Dollar , E. Struckhoff , R.S. Cohen. Dept Molec Biosci, Univ Kansas, Lawrence, KS.

   Localization of cytoplasmic determinants in the oocyte is critical for proper patterning of the egg and future embryo. This localization is the culmination of a polarization response triggered in the oocyte by posterior follicle cells. One crucial element of this response is the formation of a polarized microtubule cytoskeleton along which molecules can be directed to the anterior or posterior pole. Here we present evidence that another crucial element of this response is polarization of the oocyte plasma membrane. We show that rab11, a membrane trafficking gene, is required in the oocyte to maintain the polarized microtubule cytoskeleton. In rab11mutant oocytes, the growing ends of microtubules are no longer concentrated at the posterior pole, and posterior determinants are no longer localized. In mammalian cell culture systems, Rab11 recycles endocytosed receptors back to the plasma membrane from the recycling endosome. We show that Rab11 maintains this function in Drosophila. Rab11 is localized to the posterior pole of mid-stage oocytes, where it preferentially targets vesicles containing endocytosed receptors to the posterior plasma membrane. Furthermore, we see evidence of a posterior plasma membrane polarity that forms roughly coincident to wild-type Rab11 localization, and is absent from rab11mutant oocytes. Our data indicates that polarization of the plasma membrane, achieved through targeted recycling of membrane components to the posterior pole, is part of the polarization response of the oocyte, and that a loss of membrane polarity results in a loss of cytoplasmic polarity and patterning defects of the egg and embryo.