Induction and maintenance of flattened morphology in highly adhesive friend leukemia clones depends on the time‐ and space‐specific assembly of microtubular networks

Abstract

Indirect immunofluorescent staining with anti-tubulin antibodies, SEM and TEM were applied to study microtubule (MT) assembly in clones isolated from Friend leukemia cells (FLC, 745 A strain) on the basis of their sensitivity to exogenous fibronectin (FN). Kinetics of cell spreading and elongation were studied using computerized image analysis and SEM. In contrast to 745 A cells, FN-sensitive clones (referred to as FF clones) showed elaborate MT networks when observed by immunofluorescent staining as well as by TEM. A good correlation was found between the degree of spreading and elongation of FF cells and the degree and cellular distribution of their MT. The highest concentration of MT networks oriented parallel to the main cellular axis was observed in very elongated FF cells. The majority of MT in interphase FF cells radiated from the centrosomes; some MT apparently originated from the nuclear membranes. TEM showed the existence of morphological differences between centrosomes of 745 A and FF cells. The characteristic ultrastructure of the centrosomes of FF cells was maintained in trypsinized cells, even if such FF cells lost MT's and acquired a spherical morphology. FF cells, treated with a wide spectrum of MT-disrupting agents, promptly acquired a rounded morphology with rapid dissolution of polymerized tubulin. Removal of MT-disrupting agents from the culture medium rapidly restored a flattened morphology with concurrent regeneration of MT's. During recovery from MT-disrupting agents, FF cells showed increased numbers of centrosomes per cell. We conclude that MT networks cooperate in the attachment, spreading and elongation of FF cells isolated from FLC. Moreover, we hypothesize the existence in FF cells of a variant form of centrosomes as compared with those of 745 A cells.

Reduced maturation of friend virus in adhesive mutants of friend leukemia cells

“…The ultrastructural details of 745 A and FF cells have already been reported (11). We describe here some features which may be relevant to such understanding of the control of FLV replication in the two types of cells.…”

“…Sparse and confluent FF cell monolayers were fixed in situ as described elsewhere (11). Both types of cells were embedded in Epon 812, cut with diamond knives (SAG International), stained with Ultrostainer (LKB, Sweden) set at standard values.…”