The pericentriolar material in Chinese hamster ovary cells nucleates microtubule formation

Abstract

The structure and function of the centrosomes from Chinese hamster ovary (CHO) cells were investigated by electron microscopy of negatively stained whole mount preparations of cell lysates. Cells were trypsinized from culture dishes, lysed with Triton X 100, sedimented onto ionized, carbon coated grids, and negatively stained with phosphotungstate. The centrosomes from both interphase and dividing cells consisted of pairs of centrioles, a fibrous pericentriolar material and a group of virus like particles which were characteristic of the CHO cells and which served as markers for the pericentriolar material. Interphase centrosomes anchored up to two dozen microtubules when cells were lysed under conditions which preserved native microtubules. When Colcemid blocked mitotic cells, initially devoid of microtubules, were allowed to recover for 10 min, microtubules formed at the pericentriolar material, but not at the centrioles. When lysates of Colcemid blocked cells were incubated in vitro with microtubule protein purified from porcine brain tissue, up to 250 microtubules assembled at the centrosomes, similar to the number of microtubules that would normally form at the centrosome during cell division. A few microtubules could also be assembled in vitro onto the ends of isolated centrioles from which the pericentriolar material had been removed, forming characteristic axoneme like bundles. In addition, microtubules were assembled onto fragments of densely staining, fibrous material which was tentatively identified as pericentriolar material by its association with the virus like particles. We conclude that the pericentriolar material of CHO can initiate and anchor microtubules both in vivo and in vitro.