The Production of Multinucleated Lymphocytes by Cytochalasin B. An Electron Microscopic Study

Abstract

The cytochalasins are newly derived from moulds and are useful in studying nuclear division. Multinucleated fibroblasts were produced by CARTER [Nature 213: 261, 1967] and lymphocytes by us [Nature 216: 1134, 1967]. Lymphocytes with up to eight nuclei were seen. Progressive nuclear addition [1, 2, 3 etc.) was found instead of a doubling of the nuclei (1, 2, 4, etc.). The term ‘pseidomitosis’ was proposed for the process of synchronous mitosis, but which results in the division of only one nuclei.Our observations, using the light microscope shows the nuclei of binucleated cells to be similar in size and shape; however, in cells with more than two nuclei there is marked vaiation in size and shape of each nucleus. What might have appeared, in many instances, as separate nuclei are seen by electron microsopy to be lobes of a rather large and irregular nucleus. In other instances, small nuclear bridges connected what might appear as separate nuclei. Variation exists in nuclear size from rather large nuclei to very small micronuclei. Serial sectioning of cell nuclei verified the morphological variability seen in single sections. Spindle fibers and kinetochore attachment to the chromosomes revealed no unusual features. Electron microscopy showed synchronous division of nuclei. Golgi apparatus remained as a single large unit. There was a doubling of centrioles in binucleated cells. What appears as separate nuclei under the light microscope were connected by nuclear bridges. The finding suggests that as nuclei accumulate that the spindle bridge is unable to accurately divide the large numbers of chromosomes present.