MICROTUBULES ARE REQUIRED IN AMEBA CHEMOTAXIS FOR PREFERENTIAL STABILIZATION OF APPROPRIATE PSEUDOPODS

Amoebae of Physarum polycephalum exhibit chemotactic responses to gluc ose and to cAMP. The chemotaxing amoebae exhibit alternating locomotiv e movements: relatively linear locomotion and movements that change th e direction of the locomotion. Such locomotive activity is tightly cou pled with the changes in the number and the positions of the pseudopod s; cells have one pseudopod at the leading edge during their linear lo comotion, while they have multiple pseudopods when they are changing t he direction of locomotion. Treatment of cells with microtubule-disrup ting reagents inhibited the chemotaxis of the cells. To characterize t he role of the microtubule system in chemotaxis, we quantitatively ana lyzed the relationship between the positions of multiple pseudopods of the amoebae and the relative stability of the pseudopods during reori entation. No significant differences were observed in the pseudopod dy namics between the untreated and the treated amoebae. In both cases, o ne pseudopod at the leading edge continued to expand during linear loc omotion. It then split into two to three pseudopods in the reorientati on phase, and the positions of the multiple pseudopods were random. Am ong multiple pseudopods, however, the pseudopods closer to the microne edle tip were selectively stabilized more often than those distant fro m the tip in the presence of the microtubule system. By contrast, such preferential stabilization of the appropriate pseudopods was complete ly abolished by microtubule inhibitors. The microtubule-dependent sele ction of appropriately located pseudopods enables amoebae to turn corr ectly at the reorientation step.