The vesicular compartment of the mitotic apparatus in mammalian cells.

Intracellular membranes might play an eminent role in regulating several events during mitosis: In this paper the appearance and changing configurations of the vesicular compartment of the mitotic apparatus of HeLa cells was studied from anaphase to telophase. In early prophase electron opaque and transparent membranous vesicles are found in the pericentriolar region outside the nucleus. During prometaphase when the nuclear envelope opens and starts to disappear, an increasing number of these vesicles appears in the mitotic apparatus near the chromosomes. During metaphase vesicles are spread all over the mitotic apparatus, the number of electron opaque vesicles decreases while the total amount of vesicles does not change significantly. Anaphase shows the same pattern of distribution in the half-spindle and in the midbody. In telophase the amount of electron opaque vesicles increases again. They are now found around vacuoles and near the newly appearing Golgi-cisternae. We assume that the electron opaque vesicles are derived from the Golgi- apparatus which disintegrates during prophase and reappears in late telophase. The change in the appearance of the different types of vesicles during metaphase coincides with drastic changes in the ionic milieu in the mitotic apparatus (Wolniak et al., 1983).