Figure 9. Amplification of hecate/grip2a-dependent symmetry breaking event by a general animal-directed long-range transport system.

A) Cortical shifts of various vegetally localized components, including wnt8a mRNA, Sybu protein and grip2a mRNA ([6], [7], [8]; this report) are short-range and dependent on microtubule bundling and alignment, itself dependent on hec function. In wild-type embryos, such a short-range shift generates a symmetry breaking event that is subsequently amplified by long-range, animally-directed transport mechanism independent of hec function and not restricted to the prospective dorsal axis. B) In hec mutant embryos, neither reorganization of vegetal microtubules into aligned bundles nor a short-range shift occur, so that, even though long-range transport remains intact, vegetal determinant transport to the animal pole is affected. The mechanistic basis for the long-range transport, occurring in the region of a loosely organized mediolateral microtubule cortical network remains to be determined (see Discussion).