INDEPENDENCE OF 2 MICROTUBULE SYSTEMS IN FERTILIZED FROG EGGS - THE SPERM ASTER AND THE VEGETAL PARALLEL ARRAY

Two microtubule-containing structures are implicated in dorsoventral p olarization of the frog egg, and we examined the relationship between them. The sperm aster provides a directional cue for a cortical rotati on specifying polarity, and a vegetal cortical array of parallel micro tubules is likely part of the rotational machinery. The growing aster has an accumulation of microtubules marking the path of the sperm pron ucleus, and its microtubules extend into the egg cortex as well as the cytoplasm. To test whether the vegetal parallel array was an extensio n of astral cortical growth, fertilized or activated eggs were bisecte d into animal and vegetal fragments. The vegetal fragments formed para llel arrays, even when isolated within a few minutes of egg activation . Neither the sperm centrosome nor another microtubule organizing cent er in the animal half of the egg is required for formation of the para llel array, but some animal half activity is involved in its disappear ance.