The glycosylphosphatidylinositol-PLC in Trypanosoma brucei forms a linear array on the exterior of the flagellar membrane before and after activation.

Bloodstream forms of Trypanosoma brucei contain a glycosylphosphatidylinositol-specific phospholipase C (GPI-PLC) that cleaves the GPI-anchor of the variable surface glycoprotein (VSG). Its location in trypanosomes has been controversial. Here, using confocal microscopy and surface labelling techniques, we show that the GPI-PLC is located exclusively in a linear array on the outside of the flagellar membrane, close to the flagellar attachment zone, but does not co-localize with the flagellar attachment zone protein, FAZ1. Consequently, the GPI-PLC and the VSG occupy the same plasma membrane leaflet, which resolves the topological problem associated with the cleavage reaction if the VSG and the GPI-PLC were on opposite sides of the membrane. The exterior location requires the enzyme to be tightly regulated to prevent VSG release under basal conditions. During stimulated VSG release in intact cells, the GPI-PLC did not change location, suggesting that the release mechanism involves lateral diffusion of the VSG in the plane of the membrane to the fixed position of the GPI-PLC.

Images of mitochondrial UCP 1 in mouse thymocytes using confocal microscopy.

The aim of this study was to demonstrate the constitutive expression of mitochondrial uncoupling protein 1 (UCP 1) in pure thymocytes using laser scanning confocal microscopic imagery. To that end we probed thymocytes from UCP 1 knock-out and wild-type mice. Mitochondrial location in thymocytes was determined using Mitotracker Red and the nucleus was labelled using Hoescht stain. We demonstrate that all cells investigated were thymocytes as determined by a monoclonal antibody specific for the thymocyte surface marker Thy 1 (CD90) pre-coupled to a fluorescent labelled (Alexa 448, green). Using a primary peptide antibody specific to UCP 1, and secondary fluorescently labelled (Alexa 647, magenta) antibody, we were able to demonstrate that UCP 1 is associated with mitochondria in thymocytes from UCP 1 wild-type mice but not thymocytes from UCP1-knock-out mice. These are the first images demonstrating the presence of UCP 1 in thymocyte mitochondria, in situ, and the first to clearly demonstrate UCP 1 expression in cells other than brown adipocytes. We conclude that mouse thymocytes contain UCP 1 in their mitochondria.

Advanced microscopy: laser scanning confocal microscopy.

Fluorescence microscopy is an important and fundamental tool for biomedical research. Optical microscopy is almost non-invasive and allows highly spatially resolved images of organisms, cells, macromolecular complexes, and biomolecules to be obtained. Generally speaking, the architecture of the observed structures is not significantly modified and the environmental conditions can be kept very close to physiological reality. The development of fluorescence microscopy was revolutionized with the invention of laser scanning confocal microscopy (LSCM). With its unique three-dimensional representation and analysis capabilities, this technology gives us a more real view of the world.This chapter introduces the reader to the methodology of setting up basic experiments for use with a laser scanning confocal microscope. There are practical guidelines about sample preparation for both fixed and living specimens, as well as examples of some of the applications of confocal microscopy.

Identification and characterization of an unusual class I myosin involved in vesicle traffic in Trypanosoma brucei.

Myosins are a multimember family of motor proteins with diverse functions in eukaryotic cells. African trypanosomes possess only two candidate myosins and thus represent a useful system for functional analysis of these motors. One of these candidates is an unusual class I myosin (TbMyo1) that is expressed at similar levels but organized differently during the life cycle of Trypanosoma brucei. This myosin localizes to the polarized endocytic pathway in bloodstream forms of the parasite. This organization is actin dependent. Knock down of TbMyo1 results in a significant reduction in endocytic activity, a cessation in cell division and eventually cell death. A striking morphological feature in these cells is an enlargement of the flagellar pocket, which is consistent with an imbalance in traffic to and from the surface. In contrast TbMyo1 is distributed throughout procyclic forms of the tsetse vector and a loss of approximately 90% of the protein has no obvious effects on growth or morphology. These results reveal a life cycle stage specific requirement for this myosin in essential endocytic traffic and represent the first description of the involvement of a motor protein in vesicle traffic in these parasites.

Measuring autophagy in macrophages.

Macroautophagy is a conserved intracellular homeostatic mechanism for the degradation of cytosolic constituents. Autophagy can promote cell survival by providing essential amino acids from the breakdown of macromolecules during periods of nutrient deprivation, and can remove damaged or excess organelles, such as mitochondria and peroxisomes. More recently, autophagy has been shown to play an important role in innate and adaptive immune responses to pathogenic bacteria in macrophages and dendritic cells. This unit presents protocols for the measurement of autophagy in macrophages.

Characterisation of the plasma membrane subproteome of bloodstream form Trypanosoma brucei.

Proteome analysis by conventional approaches is biased against hydrophobic membrane proteins, many of which are also of low abundance. We have isolated plasma membrane sheets from bloodstream forms of Trypanosoma brucei by subcellular fractionation, and then applied a battery of complementary protein separation and identification techniques to identify a large number of proteins in this fraction. The results of these analyses have been combined to generate a subproteome for the pellicular plasma membrane of bloodstream forms of T. brucei as well as a separate subproteome for the pellicular cytoskeleton. In parallel, we have used in silico approaches to predict the relative abundance of proteins potentially expressed by bloodstream form trypanosomes, and to identify likely polytopic membrane proteins, providing quality control for the experimentally defined plasma membrane subproteome. We show that the application of multiple high-resolution proteomic techniques to an enriched organelle fraction is a valuable approach for the characterisation of relatively intractable membrane proteomes. We present here the most complete analysis of a protozoan plasma membrane proteome to date and show the presence of a large number of integral membrane proteins, including 11 nucleoside/nucleobase transporters, 15 ion pumps and channels and a large number of adenylate cyclases hitherto listed as putative proteins.