@article{KruegerBatsiosBaumannetal.2012, author = {Kr{\"u}ger, Anne and Batsios, Petros and Baumann, Otto and Luckert, Eva and Schwarz, Heinz and Stick, Reimer and Meyer, Irene and Gr{\"a}f, Ralph}, title = {Characterization of NE81, the first lamin-like nucleoskeleton protein in a unicellular organism}, series = {Molecular biology of the cell : the official publication of the American Society for Cell Biology}, volume = {23}, journal = {Molecular biology of the cell : the official publication of the American Society for Cell Biology}, number = {2}, publisher = {American Society for Cell Biology}, address = {Bethesda}, issn = {1059-1524}, doi = {10.1091/mbc.E11-07-0595}, pages = {360 -- 370}, year = {2012}, abstract = {Lamins build the nuclear lamina and are required for chromatin organization, gene expression, cell cycle progression, and mechanical stabilization. Despite these universal functions, lamins have so far been found only in metazoans. We have identified protein NE81 in Dictyostelium, which has properties that justify its denomination as a lamin-like protein in a lower eukaryote. This is based on its primary structure, subcellular localization, and regulation during mitosis, and its requirement of the C-terminal CaaX box as a posttranslational processing signal for proper localization. Our knockout and overexpression mutants revealed an important role for NE81 in nuclear integrity, chromatin organization, and mechanical stability of cells. All our results are in agreement with a role for NE81 in formation of a nuclear lamina. This function is corroborated by localization of Dictyostelium NE81 at the nuclear envelope in human cells. The discovery of a lamin-like protein in a unicellular organism is not only intriguing in light of evolution, it may also provide a simple experimental platform for studies of the molecular basis of laminopathies.}, language = {en} } @article{BatsiosPeterBaumannetal.2012, author = {Batsios, Petros and Peter, Tatjana and Baumann, Otto and Stick, Reimer and Meyer, Irene and Gr{\"a}f, Ralph}, title = {A lamin in lower eukaryotes?}, series = {Nucleus}, volume = {3}, journal = {Nucleus}, number = {3}, publisher = {Landes Bioscience}, address = {Austin}, issn = {1949-1034}, doi = {10.4161/nucl.20149}, pages = {237 -- 243}, year = {2012}, abstract = {Lamins are the major components of the nuclear lamina and serve not only as a mechanical support, but are also involved in chromatin organization, epigenetic regulation, transcription and mitotic events. Despite these universal tasks, lamins have so far been found only in metazoans. Yet, recently we have identified Dictyostelium NE81 as the first lamin-like protein in a lower eukaryote. Based on the current knowledge, we draw a model for nuclear envelope organization in Dictyostelium in this Extra View and we review the experimental data that justified this classification. Furthermore we provide unpublished data underscoring the requirement of posttranslational CaaX-box processing for proper protein localization at the nuclear envelope. Sequence comparison of NE81 sequences from four Dictyostelia with bona fide lamins illustrates the evolutional relationship between these proteins. Under certain conditions these usually unicellular social amoebae congregate to form a multicellular body. We propose that the evolution of the lamin-like NE81 went along with the invention of multicellularity.}, language = {en} } @article{KuhnertBaumannMeyeretal.2012, author = {Kuhnert, Oliver and Baumann, Otto and Meyer, Irene and Gr{\"a}f, Ralph}, title = {Functional characterization of CP148, a novel key component for centrosome integrity in Dictyostelium}, series = {Cellular and molecular life sciences}, volume = {69}, journal = {Cellular and molecular life sciences}, number = {11}, publisher = {Springer}, address = {Basel}, issn = {1420-682X}, doi = {10.1007/s00018-011-0904-2}, pages = {1875 -- 1888}, year = {2012}, abstract = {The centrosome consists of a layered core structure surrounded by a microtubule-nucleating corona. A tight linkage through the nuclear envelope connects the cytosolic centrosome with the clustered centromeres within the nuclear matrix. At G2/M the corona dissociates, and the core structure duplicates, yielding two spindle poles. CP148 is a novel coiled coil protein of the centrosomal corona. GFP-CP148 exhibited cell cycle-dependent presence and absence at the centrosome, which correlates with dissociation of the corona in prophase and its reformation in late telophase. During telophase, GFP-CP148 formed cytosolic foci, which coalesced and joined the centrosome. This explains the hypertrophic appearance of the corona upon strong overexpression of GFP-CP148. Depletion of CP148 by RNAi caused virtual loss of the corona and disorganization of interphase microtubules. Surprisingly, formation of the mitotic spindle and astral microtubules was unaffected. Thus, microtubule nucleation complexes associate with centrosomal core components through different means during interphase and mitosis. Furthermore, CP148 RNAi caused dispersal of centromeres and altered Sun1 distribution at the nuclear envelope, suggesting a role of CP148 in the linkage between centrosomes and centromeres. Taken together, CP148 is an essential factor for the formation of the centrosomal corona, which in turn is required for centrosome/centromere linkage.}, language = {en} } @article{KuhnertBaumannMeyeretal.2012, author = {Kuhnert, Oliver and Baumann, Otto and Meyer, Irene and Gr{\"a}f, Ralph}, title = {CP55, a novel key component of centrosomal organization in dictyostelium}, series = {Cellular and molecular life sciences}, volume = {69}, journal = {Cellular and molecular life sciences}, number = {21}, publisher = {Springer}, address = {Basel}, issn = {1420-682X}, doi = {10.1007/s00018-012-1040-3}, pages = {3651 -- 3664}, year = {2012}, abstract = {Dictyostelium centrosomes consist of a layered core structure surrounded by a microtubule-nucleating corona. At the G2/M transition, the corona dissociates and the core structure duplicates, yielding two spindle pole bodies. Finally, in telophase, the spindle poles mature into two new, complete centrosomes. CP55 was identified in a centrosomal proteome analysis. It is a component of the centrosomal core structure, and persists at the centrosome throughout the entire cell cycle. FRAP experiments revealed that during interphase the majority of centrosomal GFP-CP55 is immobile, which indicates a structural task of CP55 at the centrosome. The CP55null mutant is characterized by increased ploidy, a less structured, slightly enlarged corona, and by supernumerary, cytosolic MTOCs, containing only corona proteins and lacking a core structure. Live cell imaging showed that supernumerary MTOCs arise in telophase. Lack of CP55 also caused premature recruitment of the corona organizer CP148 to mitotic spindle poles, already in metaphase instead of telophase. Forces transmitted through astral microtubules may expel prematurely acquired or loosely attached corona fragments into the cytosol, where they act as independent MTOCs. CP55null cells were also impaired in growth, most probably due to difficulties in centrosome splitting during prophase. Furthermore, although they were still capable of phagocytosis, they appeared unable to utilize phagocytosed nutrients. This inability may be attributed to their partially disorganized Golgi apparatus.}, language = {en} }