THE CENTROSOMAL CYCLE - VISUALIZATION IN PTK CELLS BY A MONOCLONAL-ANTIBODY TO A CENTROSOMAL-32 KD PROTEIN

A monoclonal antibody prepared against a crude centrosome fraction from PtK cells reacts exclusively with centrosomes. Using Western blotting techniques, the antigen was identified as a protein with a molecular weight of 32 kd. Using this probe it is possible to follow pronounced shape changes of the centrosome through the cell cycle and to study its replication. When the microtubular cytoskeleton is removed by nocodazole, neither the shape nor the three-dimensional organization of the centrosome inside the cell are altered. Moreover, in spite of the cell cycle arrest caused by nocodazole, the centrosomal cycle proceeds, thus indicating its independence from the intact cytoskeleton and supporting its role as a semi-autonomous organelle. On the basis of these results we hypothesize that the centrosome has two distinct functions: in the non-growing compact state during mitosis the centrosome serves as the pole organizer and during interphase it functions as the ''cytocenter''.