[Ciliopaties - diseases caused by abnormal cilia functioning]

Ciliopathies are a group of genetic diseases caused by defects in the function of cilia, that are cellular processes composed of a microtubule-based core. Ciliopathies present with pathological changes in one or many organs at the same time. Symptoms of ciliopathies depend on the type of damaged tissues and organs. The most common are polycystic kidney and liver, blindness, dysfunction of neural tube, brain anomalies, mental retardation, abnormalities in skeletal system from polydactyly to abnormal short ribs and limbs, abnormalities in ectoderms, obesity, situs inversus, infertility and infections of the upper airways. Both basic and clinical studies provide data regarding novel ciliary proteins the lack or mutation of which are associated with cilia dysfunction and which, in consequence, may give rise to ciliopathies. The number of ciliopathies (35 known at present) is still increasing due to identification of additional genes (187 identified up to now) directly connected with these diseases. In this work, the most important mechanisms responsible for abnormal cilia formation and functioning, that constitute the primary cause of ciliopathies, are presented.

[Microtubule severing proteins - structure and activity regulation]

Microtubule severing proteins, katanin, spastin and fidgetin cause local destabilization of the microtubules structure. This ATP-dependent activity leads to the shortening or disassembly of the existing microtubules. The generated short microtubule fragments may serve as templates to polymerize new microtubules and in consequence, the activity of the microtubule severing proteins leads to the reorganization of the microtubular cytoskeleton. This review summarizes current knowledge concerning structural organization of the microtubule severing proteins, the molecular mechanism of their action, factors that regulate the level of the katanin and spastin within the cells and their microtubule severing activity.

[Role of microtubule severing proteins in cytoskeleton reorganization]

ATP-dependent severing activity of microtubule severing proteins leads to the local destabilization of the microtubule structure and causes shortening or disassembly of the existing microtubules or formation of the numerous short microtubule fragments that serve as templates during new microtubule polymerization. Microtubule severing protein-dependent rearrangement of the microtubular cytoskeleton plays an important role in the numerous cellular processes including chromosome segregation during meiosis and mitosis, cells migration, dendrites and axon formation, cilia assembly and arrangement of the cortical microtubules in plant cells.

PHLP2 is essential and plays a role in ciliogenesis and microtubule assembly in Tetrahymena thermophila

Recent studies have implicated the phosducin-like protein-2 (PHLP2) in regulation of CCT, a chaperonin whose activity is essential for folding of tubulin and actin. However, the exact molecular function of PHLP2 is unclear. Here we investigate the significance of PHLP2 in a ciliated unicellular model, Tetrahymena thermophila, by deleting its single homolog, Phlp2p. Cells lacking Phlp2p became larger and died within 96 h. Overexpressed Phlp2p-HA localized to cilia, basal bodies, and cytosol without an obvious change in the phenotype. Despite similar localization, overexpressed GFP-Phlp2p caused a dominant-negative effect. Cells overproducing GFP-Phlp2p had decreased rates of proliferation, motility and phagocytosis, as compared to wild type cells or cells overproducing a non-tagged Phlp2p. Growing GFP-Phlp2p-overexpressing cells had fewer cilia and, when deciliated, failed to regenerate cilia, indicating defects in cilia assembly. Paclitaxel-treated GFP-Phlp2p cells failed to elongate cilia, indicating a change in the microtubules dynamics. The pattern of ciliary and cytosolic tubulin isoforms on 2D gels differed between wild type and GFP-Phlp2p-overexpressing cells. Thus, in Tetrahymena, PhLP2 is essential and under specific experimental conditions its activity affects tubulin and microtubule-dependent functions including cilia assembly.