MICROTUBULE BIOGENESIS AND CELL SHAPE IN OCHROMONAS

Abstract

The role of microtubules and microtubule nucleating sites in the unicell, Ochromonas has been examined through the use of two mitotic inhibitors, isopropyl N-phenylcarbamate (IPC) and isopropyl N-3-chlorophenyl carbamate (CIPC) . Although IPC and CIPC have little or no effect on intact microtubules, the assembly of three separate sets of microtubules in Ochromonas has been found to be differentially affected by IPC and CIPC . The assembly of flagellar microtubules after mechanical deflagellation is partially inhibited ; the reassembly of rhizoplast microtubules after pressure depolymerization is totally inhibited (however, macrotubules may form at the sites of microtubule initiation or elsewhere) ; and, the reassembly of the beak set of microtubules after pressure depolymerization may be unaffected although similar concentrations of IPC and CICP completely inhibit microtubule regeneration on the rhizoplast . These effects on microtubule assembly, either inhibitory or macrotubule inducing, are fully reversible . The kinetics of inhibition and reversal are found to be generally similar for both flagellar and cell shape regeneration . Incorporation data suggest that neither IPC nor CIPC has significant effects on protein synthesis in short term experiments . Conversely, inhibiting protein synthesis with cycloheximide has little effect on microtubule regeneration when IPC or CIPC is removed . Although the exact target for IPC and CIPC action remains uncertain, the available evidence suggests that the microtubule protein pool or the microtubule nucleating sites are specifically and reversibly affected . Comparative experiments using the mitotic inhibitor colchicine indicate some similarities and differences in its mode of action with respect to that of IPC and CIPC on assembly and disassembly of microtubules in these cells .In the first two papers of this series (Bouck and ently independent sets of cytoplasmic microBrown, 1973 ; Brown and Bouck, 1973) evidence tubules which (a) differ from each other in sensiwas presented that the characteristic asymmetric tivity to the microtubule depolymerizing agents shape of Ochromonas is mediated by two appar-colchicine and hydrostatic pressure, (b) are 514

The effects of Isopropyl-N-Phenylcarbomate on meiotic maturation of mammalian oocytes

“…These results correspond with those obtained on other cells lacking centrioles : algae (Coss and Pickett-Heaps, 1974) unicellular organisms (Mergulis, and Banerjee, 1969 ;Brown and Bouck, 1974), plant cells (Hepler and Jackson, 1969 ;Hervas, 1974) and tend to demonstrate that IPC reacts with MTOCs and not directly with microtubules ; but its mechanism of action remains still unknow.…”

Contraction of chromosomes and depression of RNA synthesis by isopropyl N-(3-chlorophenyl) carbamate (CIPC) in Vicia faba root tip cells.

“…Colchicine binds to subunits of microtubules and prevents their poly merization (Hart and Sabnis 1977). On the other hand, several studies have con firmed that IPC and CIPC do not bind to microtubules nor do they prevent the polymerization of microtubule proteins (Bartels and Hilton 1973, Brown andBouck 1974, Coss et al 1975). Microtubules of IPC-or CIPC-treated cells do not disap pear but instead are aggregated in inappropriate ways or on inappropriate organelles (Hepler and Jackson 1969), cf: Dustin (1978).…”

Effect of Digitonin on Cellular Division Part VI

“…Moreover, these tubules disappeared during recovery of the cold-treated cells. Brown and Bouck (1971) found in Ochromonas that microtubules disappear in IPC-treated cells subjected to hydrostatic pressure, and "macrotubules" (350 to 400 A in diameter) appear at sites of microtubule dis assembly. In addition, Burton and Fernandez (1971) found in some axons of the ventral nerve cord of crayfish that hyaluronidase induces formation of "macrotubules" 400 to 500 A in diameter.…”