Basal body-associated nucleation center for the centrin-based cortical cytoskeletal network in Paramecium

The infraciliary lattice, a contractile cortical cytoskeletal network of Paramecium, is composed of a small number of polypeptides including centrins. Its overall pattern reflects a hierarchy of structural complexity, from assembly and bundling of microfilaments to formation of polygonal meshes arranged in a continuous network subtending the whole cell surface, with local differentiations in the shape and size of the meshes. To analyse how the geometry of this complex network is generated and maintained, we have taken two approaches. Firstly, using monoclonal antibodies raised against the purified network, we have shown that all the component polypeptides colocalize, in agreement with previous biochemical data indicating that the infraciliary lattice is formed of large complexes comprising all the component polypeptides. Secondly, by taking advantage of different experimental conditions leading to disassembly of the network, we have followed its reassembly. Cytological analysis of the process revealed 1) that the network regrows exclusively from specific infraciliary lattice organizing centers (ICLOC), precisely localized near each basal body and, 2) that the global organization is not precisely controlled by genetic information but by the basal body pattern. Finally, slight ultrastuctural differences between reassembled and control lattices suggest that the organization of the filament bundles is partly templated by that of the preexisting ones.