Patterning in opalinids: II. Endocytofibrillar complex in Protoopalina pseudonutti Sandon, 1976

Abstract

Summary At certain phases of the life cycle of Protoopalina pseudonutti silver impregnation according to the technique of Fernandez-Galiano reveals a large axial fibrillar complex which divides into numerous lateral branches linked to the falcular zone and the somatic kineties. An electron microscopy study, using a new method of fixation, confirmed the existence of a well-developed fibrillar network composed of microfibrillar bundles with irregularly spaced dense zones. It continues in the falcular matrix and branches extensively, producing lateral expansions, some of which extend along the somatic kineties. Others surround the nuclei which, during interphase and division, also carry a thin microfibrillar layer on the cytoplasmic face of the nuclear envelope. This fibrillar network extends caudally and forms the framework of the tip. In its morphology and ultrastructural organization, this network is similar to certain skeletal constituents observed in ciliates, such as the ecto-endoplasmic boundary of the rumen ciliates. It could thus also be composed of centrin-like proteins and has resemblances to the cortical network which characterizes the species Opalina ranarum. Consequently, it may play a role in cell morphogenesis. Its development, which in some species is more pronounced, and its location varies according to the morphology of the cell and the number of nuclei or both. In species with few nuclei cytoskeletal differentiation is required to control the positioning of the nuclei to ensure the transmission of genetic information.