Micromanipulation Experiments Research Articles

Microtubule-dependent reticulopodial motility: is there a role for actin?

We summarize our recent immunocytochemical characterization of the reticulopodial cytoskeleton of two allogromiid foraminifers and our pharmacologic dissection of its motility. The reticulopodial microtubule cytoskeleton stained with an antiserum to brain microtubule-associated protein 2. Polymeric actin was localized in the reticulopodia by rhodamine-phalloidin staining. Microtubule inhibitors reversibly inhibited all aspects of motility; cytochalasins induced altered morphology and disorganization of motility but did not inhibit pseudopodial movements or intracellular transport. Simultaneous application of KCN and salicylhydroxamic acid (an alternative oxidase inhibitor) rapidly blocked all movement, indicating that motility is dependent on metabolic energy and that an alternative oxidative pathway functions in allogromiids. Micromanipulation and laser microsurgical experiments revealed tension throughout the reticulopodium. Our results suggest that microtubules are active components of the reticulopodial motile machinery. Actin may mediate substrate adhesion, whole-cell locomotion, pseudopodial tension, and coordination of the microtubule-based motility.

Studies on the Mechanism of T Cell-Mediated Lysis at the Single Effector Cell Level

Abstract A procedure has been previously developed to allow kinetic analysis of target cell lysis in individual conjugates formed between murine alloimmune peritoneal exudate lymphocytes (PEL) and relevant tumor cells in suspension. Under the conditions used in the present work, 60% of the conjugates consisted of one lymphocyte bound to one target cell, whereas the remaining were multicellular, i.e., contained one lymphocyte bound to either two (24%), three (12%), or four (4%) target cells. Both ultrastructural studies and micromanipulation experiments with individual multicellular conjugates indicated differences in the degree of target cell binding to the same PEL. In more than 80% of the multicellular conjugates, lysis of all conjugated target cells occurred within a 3-hr incubation period at 37°C. Kinetic analysis of target cell lysis, however, showed that the time required for target cell death was quite variable, both within the same multicellular conjugate and between different conjugates, ranging from a few minutes to 3 hr after conjugation. By comparing the elapsed time necessary for lysis of 50% of the target cells in conjugates containing one lymphocyte bound to three target cells, it could be estimated that, on the average, lysis of the first, second, and third target cells occurred after 30, 60, and 90 min, respectively. The time required for lethal hit of each conjugated target cell was measured by adding EDTA to the incubation medium of individual multicellular conjugates at various time intervals. Evidence could be obtained that a CTL induced irreversible lesions in only one of the conjugated target cells at a time, i.e., lethal hits were given sequentially rather than simultaneously.

Chromosome distribution: experiments on cell hybrids and in vitro.

Ostergren (1951) provided a simple explanation for both chromosome distribution in mitosis and chromosome segregation in meiosis, and more recently a molecular extension of his hypothesis has been possible. This report focuses on experimental tests of these ideas. Micromanipulation experiments on cell hybrids containing both meiotic and mitotic spindles demonstrate that differences in meiotic and mitotic chromosome behavior are determined by something intrinsic to the chromosome: meiotic chromosomes transferred to a mitotic spindle (or vice versa) behave just as they normally would. The molecular explanation postulates polarized growth or binding of microtubules at kinetochores. This has just been tested in vitro by McGill & Brinkley (1975) and by Telzer, Moses & Rosenbaum (1975), and their results are reviewed. In addition, a novel method for in vitro studies is described - mechanical demembranation of cells which is compatible with quite normal chromosome movement in anaphase. After addition of microtubule subunits to a demembranated prophase cell, chromosome orientation and movement toward an aster was observed for the first time in vitro. It is concluded that important aspects of chromosome distribution are probably understood at both the cellular and molecular levels, but final tests are still required. The outlook is hopeful indeed because the gaps in our knowledge are well known - the necessity of observations on prophase is a recurrent theme - and the means of filling the gaps are in hand.