WHERE AND WHEN IS MICROTUBULE DIVERSITY GENERATED IN PARAMECIUM - IMMUNOLOGICAL PROPERTIES OF MICROTUBULAR NETWORKS IN THE INTERPHASE AND DIVIDING CELLS

Ciliates are highly differentiated cells which display extensive deplo yment of microtubular systems. Because genetic diversity of tubulin is extremely reduced in these cells microtubule diversity is mostly gene rated at the post-translational level either through direct modificati on of tubulin or through the binding of associated proteins to microtu bules. We have undertaken a systematic exploration of microtubule dive rsity in ciliates by way of production of monoclonal antibodies. Previ ously we reported the biochemical characterization of these antibodies . In addition to antibodies directed against primary sequences, we obt ained antibodies directed against post-translational modifications. In this paper. we report a detailed analysis of the distribution of the various epitopes on the microtubular networks of Paramecium, both in i nterphase cells and during division morphogenesis. Each of these antib odies decorates a subset of microtubules. Acetylation, recognized by a ntibodies TEU 318 and TEU 348, is detected on stable microtubules earl y after microtubule assembly. Epitopes recognized by two other antibod ies (TAP 952 and AXO 58) are found on a subset of stable microtubules; in addition, the TAP 952 antibody is also found on labile microtubule s; both epitopes are detected as soon as microtubule assembly occurs. In contrast, the epitope of the antibody, AXO 49, is associated with o nly a restricted subset of stable microtubules in the interphase cell, and is detected a lag-time after microtubule assembly during division morphogenesis. These data show that microtubule diversity is generate d through a time-dependent sequence and according to a definite spatia l pattern.