An Evolutionarily Conserved Coiled-Coil Protein Implicated in Polycystic Kidney Disease Is Involved in Basal Body Duplication and Flagellar Biogenesis in Trypanosoma brucei

Abstract

Eukaryotic flagella and cilia are among the most ancient of cellular organelles, and their basic architecture is conserved from protozoa to vertebrates (28). The core structure of the flagellar/ciliar axoneme comprises a membrane-bound cylinder of nine microtubule doublets plus two central singlet microtubules. Formation of the axoneme is organized by basal bodies, cylindrical organelles with walls composed of nine triplet microtubules that serve as templates for the assembly of doublet microtubules. Basal bodies and centrioles are similar in structure, and these organelles are often interchangeable in many organisms (4). The functions of flagella and cilia include roles in development, metazoan body polarity, and cell division, while many diseases involve a defect in the function of flagellar components (17).The protozoan Trypanosoma brucei is an ideal system in which to study microtubule-mediated events, because, in addition to the flagellum, the cell is highly polarized as a consequence of an ordered array of subpellicular microtubules (8,11). The trypanosome has a single flagellum that emerges from the flagellar pocket, an invagination of the plasma membrane at the posterior end of the cell (9, 21). The axoneme of kinetoplastid protozoa is attached to a lattice-like structure of a similar diameter, the PFR, extending along most of the axoneme (9). The flagellum is attached to the cell body throughout most of its length by the FAZ, which is composed of an electron-dense filament plus four cytoplasmic microtubules that originate from the basal body region (9).During cell division the trypanosome must replicate and separate several single-copy organelles present in G 1 cells, i.e., nucleus, kinetoplast, mitochondrion, basal body, and flagellum (36, 44). Ultrastructural studies have described a number of markers of cell cycle position and elucidated a number of discrete cell cycle phases (36). The first morphological event of the T. brucei cell cycle is the maturation and duplication of the basal body, which is followed by kinetoplast S phase and then nuclear S phase (36,44). During flagellum morphogenesis, the new axoneme is assembled from the recently matured basal body. New probasal bodies are formed, and the elongation and emergence of the flagellum from the flagellar pocket is fol-* Corresponding author. Present address:

Hearing in Drosophila Requires TilB, a Conserved Protein Associated With Ciliary Motility

“…Analysis of the TilB protein domain structure suggests the presence of two highly conserved domains separated by a less conserved coiled-coiled region. The protein contains an N-terminal leucine-rich repeat (LRR) domain with four clear repeats from residues 16 to 107 and two additional repeats up to residue 164 that align less well with the consensus (Xue and Goldberg 2000;Morgan et al 2005) (see Figure S1). Using the COILS algorithm (Lupas 1997), we see strong support for a coiled-coil segment after the LRR domain at residues 171-191 (data not shown).…”

“…In Trypanosoma, the tilB ortholog (Trypanosoma brucei leucine-rich testes protein, TbLRTP) associates with the basal body (Morgan et al 2005). RNAi against the trypanosome TbLRTP results in basal body duplications and thereby increases the flagellar number.…”

LRRC50, a Conserved Ciliary Protein Implicated in Polycystic Kidney Disease

“…47 Trypanosomal TbLRTP was shown to suppress basal body replication and flagellar biogenesis and to play a critical role in cell-cycle control. 48 The zebrafish TbLRTP homolog seahorse (lrrc6l) develops pronephric cysts. 5,49 We provided direct evidence that the SDS22-like LRRs present in Lrrc50 are necessary for proper protein function, because injection of a deletion construct lacking the consensus LxxLxL sequence of the first LRR did not rescue lrrc50 hu255hϪ/Ϫ ciliary dyskinesia and pronephric cyst development.…”

Mutations in zebrafish leucine-rich repeat-containing six-like affect cilia motility and result in pronephric cysts, but have variable effects on left-right patterning

“…1AЈ). Amino acids 1-383 of Lrrc6l are homologous (39% identity, 58% similarity) to an LRR-containing protein from T. brucei (AAF73195) (Morgan et al, 2005). Full-length Lrrc6l had 55% identity to X. tropicalis LRRC6 (CAJ83438.1) and 54% identity to mouse LRRC6 (AAH46277.1) (Xue and Goldberg, 2000).…”