Localization of fibrillarin in the nucleoli of ciliate species with subchromosomal organization of macronuclear genome

Abstract

SummaryFibrillarin is one of the highly evolutionary conserved nucleolar proteins. It plays an important role in the early processing and modifcation of pre-rRNA, ribosome assembly, maintenance of nuclear shape and cellular growth, and is essential for the early embryonic development. During the interphase, fibrillarin is found in nucleoli of higher eukaryotes, mainly in fibrillar centers and dense fibrillar components as well as in the Cajal bodies. At present, little is known about distribution of nucleolar proteins in ciliates. In this work, Bursaria truncatella, Paramecium multimicronucleatum and Didinium nasutum were studied. These ciliates belong to the species with subchromosomal organization of macronuclear genome. The aim of this work was to study localization of fibrillarin in their nucleoli using confocal microscopy and specific antibodies. It was shown that in the nucleoli of B. truncatella and P. multimicronucleatum fibrillarin mainly occurs in the central region of the nucleoli. In D. nasutum, on the contrary, nucleoli fibrillarin was located at the periphery of the nucleolar domain. These results are in good agreement with the electron microscopic data on morphology of the nucleoli that show an unusual, "inverted" location of the fibrillar component and the granular component in the nucleoli of D. nasutum.