  A novel assay based on micropatterning and time-lapse microscopy has been
developed for the study of nuclear migration dynamics in cultured mammalian
cells. When cultured on 10-20 um wide adhesive stripes, the motility of C6
glioma and primary mouse fibroblast cells is diminished. Nevertheless, nuclei
perform an unexpected auto-reverse motion: when a migrating nucleus approaches
the leading edge, it decelerates, changes the direction of motion and
accelerates to move toward the other end of the elongated cell. During this
process cells show signs of polarization closely following the direction of
nuclear movement. The observed nuclear movement requires a functioning
microtubular system, as revealed by experiments disrupting the main
cytoskeletal components with specific drugs. On the basis of our results we
argue that auto-reverse nuclear migration is due to forces determined by the
interplay of microtubule dynamics and the changing position of the microtubule
organizing center as the nucleus reaches the leading edge. Our assay
recapitulates specific features of nuclear migration (cell polarization,
oscillatory nuclear movement), while allows the systematic study of a large
number of individual cells. In particular, our experiments yielded the first
direct evidence of reversive nuclear motion in mammalian cells, induced by
attachment constraints.
