The effects of cytoskeleton inhibitors on cytoplasmic localization in Chaetopterus pergamentaceus.

We have treated fertilized and KC1-activated eggs of Chaetopterus pergamentaceus with microfilament and microtubule inhibitors to test the relationship of these cytoskeletal components to cytoplasmic localization. Low doses of cytochalasin B inhibited cleavage in fertilized egges. Such embryos underwent differentiation without cleavage, a process characterized by relocalization of the yolky endoplasm to the center of the uncleaved egg and by the formation of cilia. Similar treatment of KC1-activated eggs inhibited ciliation, but not endoplasmic relocalization. Reversible inhibition of the first cleavage resulted in equal cleavage and differentiation of a larva lacking an apical organ. Inhibition of the first two cleavages resulted in differentiation without cleavage. At all concentrations high enough to block mitosis, colchicine prevented ciliation and endoplasmic relocalization. Thus microtubule organization, but not microfilament organization, is required for ooplasmic reorganization and differentiation without cleavage.