A Cytological Analysis of Differentiation Without Cleavage in Cytochalasin B- and Colchicine-Treated Embryos of Chaetopterus pergamentaceus

Chaetopterus eggs undergo characteristic ooplasmic rearrangements during development. Ooplasmic rearrangement in the absence of cell division is called differentiation without cleavage. Treatment of fertilized eggs with cytochalasin B allowed the continuation of nuclear divisions in the absence of cytoplasmic division. The ooplasmic rearrangements in uncleaved cytochalasin B-treated fertilized eggs closely paralleled those of normal development. Colchicine treatment, which blocks mitosis, arrested ooplasmic movements at a stage comparable to that of normal embryos at first cleavage. Neither drug eliminated the segregation between hyaloplasm and endoplasm, even though colchicine prevented the later rearrangements. Localizing movements are therefore dependent upon normal microtubule function, but not on microfilament function. The maintenance of localized materials does not seem to depend exclusively on either of these organelles.