Fig. 7. A speculative model for slow and fast streaming in Drosophila oocytes. The lower panels represent expanded views of the regions enclosed by blue boxes in the upper panels. The underlying premise is that unidirectional transport of organelles along microtubules can impel surrounding cytoplasm to stream. (A) Before stage 10B, competition between dynein and kinesin-1 suppresses concerted plus-end organelle transport and prevents parallel ordering of microtubules, allowing only slow short-range currents. (B) During stage 10B, a dynein inhibitory signal is released from the actin-rich cortex. This allows concerted kinesin-driven organelle transport to impel strong plus-end-directed currents and sweep microtubules into parallel, but flexible, dynamic arrays.