Fig. 8. Average number of actin foci in the anterior and the posterior regions during extension and retraction phases. The boundary between the anterior and the posterior regions of the cell was defined by the perpendicular line that crossed the half point of the cell migration axis between the extreme anterior and posterior edges (small protrusions were excluded). The cell migration axis was defined from the cell centroids in three successive images (Uchida and Yumura, 1999). Both extension and retraction phases were divided into early, middle and late extension (or retraction) phases respectively, and the number of the actin foci was counted. Vertical bars showed standard errors of 11 cases of six cells. In the anterior region, the number of the actin foci did not significantly fluctuate. In the posterior region, the number of the actin foci significantly decreased (t-test, P<0.01) in the late extension phase, and then gradually increased.