The effect of local cortical microfilament disorganization on ooplasmic segregation in the loach (Misgurnus fossilis) egg.

Injections of cytochalasin D (CD) or DNase I under the surface of fertilized loach egg result in local disorganization of microfilamentous cortex (MC) as revealed by transmission electron microscopy. This effect correlates with the loss of the cortex ability to contract in vitro. The disorganization of MC in the vegetal hemisphere of the egg does not affect the ooplasm segregation or blastodisk cleavage. Injection under the animal pole suppresses blastodisk formation and results in the autonomous separation of ooplasm in the central part of the egg. The experiments suggest that (1) autonomous separation of ooplasm from the yolk granules can proceed in the central part of the egg without the participation of MC; (2) normal segregation of ooplasm at the animal pole requires that the structures of microfilaments in the animal hemisphere (but not in the vegetal one) be preserved.