(B) IFA of BF probed with mouse anti-TbFKBP12 (green). with the presence of internal translucent cavities limited by an inside-out configuration of the normal cell surface, with a luminal variant surface glycoprotein coat lined up by Ciwujianoside-B microtubules. These cavities, Ciwujianoside-B which recreated the streamlined shape of the normal trypanosome cytoskeleton, might represent unsuccessful attempts for cell abscission. We propose that TbFKBP12 differentially affects stage-specific processes through association with the cytoskeleton. INTRODUCTION African trypanosomes are extracellular protozoan flagellated parasites responsible for sleeping sickness in humans and nagana in cattle. The life cycle of encompasses different stages, including the long slender bloodstream forms (BF) proliferating in mammalian blood and the procyclic forms (PF) that actively multiply in the gut of the vector (1). Trypanosomes are among the most divergent eukaryotes in development and display specific features, many of which are related to cell division probably due to the fact that most organelles are present at one copy per cell and have to be duplicated and segregated synchronously between the daughter cells. This division involves check points that differ from those of other eukaryotes, such as the control of karyokinesis when cytokinesis is inhibited (2, 3) and vice versa (4). Molecular effectors of these check points, such as mitogen-activated protein kinase and cyclin-dependent kinase, are present in trypanosomes but diverge in function compared to other eukaryotes (5, 6). The flagellum and its motility appear to play a key role in the control of cell division (7C9). This organelle initiates Ciwujianoside-B at the basal body, which is associated to the kinetoplast (10, 11), emerges from the flagellar pocket (FP), and it is attached along the cell body for most of its length by the flagellum attachment zone (FAZ). The flagellum contains a canonical axoneme and the paraflagellar rod (PFR) that are physically linked (12C14). The duplication and segregation of these structures are interdependent. During cytokinesis, the ingression of the cleavage furrow follows an axis in between the new and the old flagellum. The position and initiation of the furrow are closely related to the FAZ, as demonstrated by the study of flagellum mutants (15C21). In eukaryotes such as yeasts or mammals the TOR pathway is a major player in the control of cell division mediated by the action of two protein complexes, TORC1 and TORC2 (22C25). These complexes contain the two different threonine/serine kinases TOR1 and TOR2 in the yeast (26C28), and one TOR protein in mammals (29). TORC1 complex controls cell mass (25, 30C32) and TORC2 the spatial aspects of cell division through cytoskeleton formation (33, 34). The role of the TOR pathway was uncovered through its inhibition by rapamycin (35). This drug, as well as a compound termed FK506, binds a cytoplasmic protein termed FKBP12 (for FK506 binding protein of 12 kDa). Binding of these compounds to FKBP12 suppresses the enzymatic peptidylprolyl isomerase (PPIase) activity of the protein (36, 37). The rapamycin/FKBP and FK506/FKBP then form ternary complexes with TOR and calcineurin, respectively (29, 30, 38, 39), leading to the inhibition of the downstream signal transduction pathways. FKBP12 binds and modulates the activity of several Ciwujianoside-B intracellular targets, such as the calcium channels ryanodine receptor (40) and inositol 1,4,5-triphosphate receptor (41, 42). In trypanosomes, two TOR proteins have been identified (43C45). In BF, their respective functions seem to match those found in other eukaryotes. They Rabbit Polyclonal to HSP90A are part of two different protein complexes with different Ciwujianoside-B cellular localizations. Gene knockdown of resulted in reduced cell growth and arrest in G1 concomitant with reduced protein synthesis, whereas RNA interference (RNAi) induced abnormal morphology and cytokinesis defects generating cells with multiple flagella and nuclei. Finally, rapamycin inhibited cell growth through interference with TOR2 but not TOR1 formation. Recently, two novel TOR kinases, TbTOR3 and TbTOR4 (formerly TbTOR-like 1 and TbTOR-like 2) were identified in the genome of (43). TbTOR3 is a cytoplasmic TOR kinase involved in polyphosphate metabolism, acidocalcisome maintenance (46), and virulence (47). TbTOR4 is involved in differentiation of.