Dynamics of the cytoskeleton during morphogenesis in the ciliate Euplotes: II. Cortex and continuous microtubular...

The dynamics of cortical growth and of the microtubular cytoskeleton have been followed in Euplotes by silver impregnation and immunocytochemical methods during the morphogenetic processes of division and conjugation. Data obtained with silver impregnation show that the growth of the cortex implies two steps: first, the nucleation of the new alveolar plates, correlated with basal body assembly, then their harmonious enlargement, leading to cirral movement. Data obtained with various anti-tubulin antibodies demonstrate the presence of two major classes of microtubular arrays: 1) A stable network, i.e. unaffected by depolymerizing treatments, made up of superficial microtubules; the microtubules belonging to this network partly originate from the classical basal bodies associated microtubular fibers, i.e. postciliary and transverse microtubules. However, some additional microtubules have to be nucleated in a basal body independent pathway to complete the network. A striking parallelism is observed between the orientation of microtubules within the superficial network and the path taken by the argyrome in the course of its growth. 2) A dynamic network located in the cytoplasm, and in which the nuclear apparatus is embedded. These two major microtubular arrays have different immunological reactivity towards a pannel of anti-tubulin antibodies. The cytoskeleton of Euplotes is thus organized as a series of interconnected systems, each of them apparently ensuring a specific function. The cellular architecture is maintained by the superficial microtubular system and the alveolar plates which act together in patterning the infraciliature. Connected to this system, the internal microtubular network seems to play a role in anchoring the nuclear system. The immunological properties of microtubular systems are discussed in relation to their suspected function in cellular organization.