Studies on the microtubules in heliozoa: IV. the effect of colchicine on the formation and maintenance of the axopodia and the redevelopment of pattern in <i>Actinosphaerium nucleofilum</i> (barrett)

Abstract

ABSTRACT When specimens of Actinosphaerium are placed in a solution of colchicine, the axopodia retract and that portion of the biréfringent core (axoneme) present in each axopodium disappears. In fixed specimens, it has been shown that the axoneme consists of a highly patterned bundle of microtubules each 220 Å in diameter. During colchicine treatment the microtubules, present in the axopodial portion of the axoneme, break down and do not reform until the cells are washed free of the colchicine and allowed to recover. In the basal portion of the axoneme or that portion confined to the cell body, most of the microtubules do not break down during colchicine treatment, although the spacing of the microbutules within the remaining axonemes is altered; in longitudinal section these tubules no longer appear straight but present an undulatory profile. When the specimens are washed free of the colchicine and allowed to recover, axopodia reform and within each numerous microtubules are present. From these observations we conclude that the microtubules are instrumental in the maintenance of the axopodia as well as in supplying the force necessary for their regrowth. Observations are also presented on the disintegration products of microtubules, on microtubules and cytoplasmic motility, and on the redevelopment of pattern. The latter is discussed at some length, for it appears that the inter-axonemal organization is somewhat modified by the colchicine treatment.