Figure 2.

Multiple interdependent relationships between pole plasm assembly and endocytosis. The polarized microtubule arrays that are induced by oocyte polarization are required for the initial activation of endocytosis at the posterior, while the increased endocytosis at the oocyte posterior maintains the plus-end targeting of microtubules to the posterior. Thus, the microtubule array polarization and local endocytic activation are interdependent (A). Polarized arrays of microtubules direct the posterior localization of osk RNA, resulting in local synthesis of the two Osk isoforms. Short Osk recruits downstream pole plasm components to the posterior, while long Osk stimulates endocytosis, thereby generating a second positive feedback loop (B). Increased endocytosis promotes the rearrangement of cortical F-actin, resulting in the formation of long F-actin projections, which anchor pole plasm components at the cortex. Because pole plasm anchoring is likely to increase the posterior localization of osk RNA, long Osk-induced endocytosis and actin remodeling form a third positive feedback loop (C).