title: Independence of two microtubule systems in fertilized frog eggs: the sperm aster and the vegetal parallel array.
abstract: Two microtubule-containing structures are implicated in dorsoventral polarization of the frog egg, and we examined the relationship between them. The sperm aster provides a directional cue for a cortical rotation specifying polarity, and a vegetal cortical array of parallel microtubules is likely part of the rotational machinery. The growing aster has an accumulation of microtubules marking the path of the sperm pronucleus, and its microtubules extend into the egg cortex as well as the cytoplasm. To test whether the vegetal parallel array was an extension of astral cortical growth, fertilized or activated eggs were bisected into animal and vegetal fragments. The vegetal fragments formed parallel arrays, even when isolated within a few minutes of egg activation. Neither the sperm centrosome nor another microtubule organizing center in the animal half of the egg is required for formation of the parallel array, but some animal half activity is involved in its disappearance.
authors.affiliation: Department of Zoology, University of Toronto, 25 Harbord Street, M5S 1Al, Toronto, Ontario, Canada.
authors.forename: Richard P
authors.initials: RP
authors.lastname: Elinson
authors.affiliation: Department of Physiology and Developmental Biology, Faculty of Science, Charles University, 12800 Vinicna 7, Prague 2, Czechoslovakia.
authors.forename: Jiří
authors.initials: J
authors.lastname: Paleček
keywords: Dorsoventral polarity; Frog embryos; Microtubules; Sperm aster