Rigidity of the nucleus during nuclear rotation in 3T3 cells

Using near infrared microscopy and ultraviolet fluorescence microscopy of living 3T3 cells stained with the fluorochrome Hoechst 33342, we have demonstrated that the nucleoli and Hoechst 33342-stained chromocenters in the nucleus maintain a fixed pattern during nuclear rotation. We conclude that the term "nuclear rotation" refers to rotation of the entire nucleus in the cytoplasm of interphase cells, and that nuclear rotation is not an expression of karyoplasmic streaming. In conjunction with earlier results on nuclear rotation the data imply that the interface of nuclear rotation is located either between the two nuclear membranes or in the adjacent cytoplasm.