Microdissection Studies on the Polarity of Unequal Division in Grasshopper Neuroblasts: II. Cell Division in Binucleate Neuroblasts

The grasshopper neuroblast divides unequally to produce two types of cells: a large daughter neuroblast that contains a doughnut-shaped nucleus and repeats unequal division with definite polarity, and a small daughter ganglion cell that has a spherical nucleus with low mitotic activity. Binucleate neuroblasts were induced by preventing cytokinesis in the course of microdissection experiments, and subsequent divisions were traced to analyze the factors that determine the polarity of unequal division.
In binucleate neuroblasts, both daughter chromosome groups developed into neuroblast-type nuclei. Mitosis of the two nuclei proceeded synchronously. Although the axes of the two mitotic apparatuses formed at late prophase were random in direction, they became parallel with the original division axis at metaphase. The two mitotic apparatuses shifted simultaneously toward the ganglion cell side during anaphase, just as in normal neuroblasts, and the binucleate cell divided unequally. These findings showed that the poearity of unequal division is strictly maintained in grasshpper neuroblasts, even when they contain two nuclei.