[Behavior of the cell center in the distribution of fibroblasts]

In suspension state of murine embryo fibroblasts the long microtubules radiating from the cell centre disappear, but many short microtubules are found around the centrioles. The growth of long microtubules begins after the cell attachment to the substrate. The number of long microtubules increases and reaches the maximum in polarized fibroblasts. At the radial spreading stage the number of microtubules increases as moving off the centriole. This fact disagrees with the statement that all microtubules in the cell are connected with the cell centre, but agrees with the hypothesis of the conveyor microtubule assembly. After the cell attachment to the substrate the centrioles move to the part of the cell facing the substrate. At the radial spreading stage the active centrioles are settled down mainly perpendicular to the plane of the substrate. Such orientation is kept after the treatment of the radially spread cells with cytochalasin B and disappears after disruption of microtubules by colcemid. It is supposed that the orientation of the active centrioles perpendicular to the substrate is connected with the formation of long microtubules during the process of spreading of fibroblasts.