A macrophage colony-stimulating factor receptor-green fluorescent protein transgene is expressed throughout the mononuclear phagocyte system of the mouse

The c-fms gene encodes the receptor for macrophage colony-stimulating factor (CSF-1). The gene is expressed selectively in the macrophage and trophoblast cell lineages. Previous studies have indicated that sequences in intron 2 control transcript elongation in tissue-specific and regulated expression of c-fms. In humans, an alternative promoter was implicated in expression of the gene in trophoblasts. We show that in mice, c-fms transcripts in trophoblasts initiate from multiple points within the 2-kilobase (kb) region flanking the first coding exon. A reporter gene construct containing 3.5 kb of 5' flanking sequence and the downstream intron 2 directed expression of enhanced green fluorescent protein (EGFP) to both trophoblasts and macrophages. EGFP was detected in trophoblasts from the earliest stage of implantation examined at embryonic day 7.5. During embryonic development, EGFP highlighted the large numbers of c-fms-positive macrophages, including those that originate from the yolk sac. In adult mice, EGFP location was consistent with known F4/80-positive macrophage populations, including Langerhans cells of the skin, and permitted convenient sorting of isolated tissue macrophages from disaggregated tissue. Expression of EGFP in transgenic mice was dependent on intron 2 as no lines with detectable EGFP expression were obtained where either all of intron 2 or a conserved enhancer element FIRE (the Fms intronic regulatory element) was removed. We have therefore defined the elements required to generate myeloid- and trophoblast-specific transgenes as well as a model system for the study of mononuclear phagocyte development and function.

mDia mediates Rho-regulated formation and orientation of stable microtubules

Rho-GTPase stabilizes microtubules that are oriented towards the leading edge in serum-starved 3T3 fibroblasts through an unknown mechanism. We used a Rho-effector domain screen to identify mDia as a downstream Rho effector involved in microtubule stabilization. Constitutively active mDia or activation of endogenous mDia with the mDia-autoinhibitory domain stimulated the formation of stable microtubules that were capped and oriented towards the wound edge. mDia co-localized with stable microtubules when overexpressed and associated with microtubules in vitro. Rho kinase was not necessary for the formation of stable microtubules. Our results show that mDia is sufficient to generate and orient stable microtubules, and indicate that Dia-related formins are part of a conserved pathway that regulates the dynamics of microtubule ends.

Visualizing lipid-formulated siRNA release from endosomes and target gene knockdown

A central hurdle in developing small interfering RNAs (siRNAs) as therapeutics is the inefficiency of their delivery across the plasma and endosomal membranes to the cytosol, where they interact with the RNA interference machinery. With the aim of improving endosomal release, a poorly understood and inefficient process, we studied the uptake and cytosolic release of siRNAs, formulated in lipoplexes or lipid nanoparticles, by live-cell imaging and correlated it with knockdown of a target GFP reporter. siRNA release occurred invariably from maturing endosomes within ~5-15 min of endocytosis. Cytosolic galectins immediately recognized the damaged endosome and targeted it for autophagy. However, inhibiting autophagy did not enhance cytosolic siRNA release. Gene knockdown occurred within a few hours of release and required <2,000 copies of cytosolic siRNAs. The ability to detect cytosolic release of siRNAs and understand how it is regulated will facilitate the development of rational strategies for improving the cytosolic delivery of candidate drugs.

Light-dependent translocation of a phytochrome B-GFP fusion protein to the nucleus in transgenic Arabidopsis

Phytochrome is a ubiquitous photoreceptor of plants and is encoded by a small multigene family. We have shown recently that a functional nuclear localization signal may reside within the COOH-terminal region of a major member of the family, phytochrome B (phyB) (Sakamoto, K., and A. Nagatani. 1996. Plant J. 10:859-868). In the present study, a fusion protein consisting of full-length phyB and the green fluorescent protein (GFP) was overexpressed in the phyB mutant of Arabidopsis to examine subcellular localization of phyB in intact tissues. The resulting transgenic lines exhibited pleiotropic phenotypes reported previously for phyB overexpressing plants, suggesting that the fusion protein is biologically active. Immunoblot analysis with anti-phyB and anti-GFP monoclonal antibodies confirmed that the fusion protein accumulated to high levels in these lines. Fluorescence microscopy of the seedlings revealed that the phyB-GFP fusion protein was localized to the nucleus in light grown tissues. Interestingly, the fusion protein formed speckles in the nucleus. Analysis of confocal optical sections confirmed that the speckles were distributed within the nucleus. In contrast, phyB-GFP fluorescence was observed throughout the cell in dark-grown seedlings. Therefore, phyB translocates to specific sites within the nucleus upon photoreceptor activation.

Clathrin-dependent and -independent internalization of plasma membrane sphingolipids initiates two Golgi targeting pathways

Sphingolipids (SLs) are plasma membrane constituents in eukaryotic cells which play important roles in a wide variety of cellular functions. However, little is known about the mechanisms of their internalization from the plasma membrane or subsequent intracellular targeting. We have begun to study these issues in human skin fibroblasts using fluorescent SL analogues. Using selective endocytic inhibitors and dominant negative constructs of dynamin and epidermal growth factor receptor pathway substrate clone 15, we found that analogues of lactosylceramide and globoside were internalized almost exclusively by a clathrin-independent ("caveolar-like") mechanism, whereas an analogue of sphingomyelin was taken up approximately equally by clathrin-dependent and -independent pathways. We also showed that the Golgi targeting of SL analogues internalized via the caveolar-like pathway was selectively perturbed by elevated intracellular cholesterol, demonstrating the existence of two discrete Golgi targeting pathways. Studies using SL-binding toxins internalized via clathrin-dependent or -independent mechanisms confirmed that endogenous SLs follow the same two pathways. These findings (a) provide a direct demonstration of differential SLs sorting into early endosomes in living cells, (b) provide a "vital marker" for endosomes derived from caveolar-like endocytosis, and (c) identify two independent pathways for lipid transport from the plasma membrane to the Golgi apparatus in human skin fibroblasts.

Bone marrow is a reservoir of repopulating mesangial cells during glomerular remodeling

The renal glomerulus, whose cellular components are developmentally derived from the mesenchyme, plays a pivotal role in filtratating plasma. Irretrievable changes of glomerular components are responsible for the initiation and progression of impaired renal function. Recently, it has been shown that functional stem cells exist in the bone marrow of adult bodies and that they can reconstitute damaged tissues of the mesenchymal origin. To examine whether the bone marrow provides stem cells to damaged glomeruli, transgenic rats carrying enhanced green fluorescence protein (EGFP rat) were established in a systemic and constitutive manner. After transplanting the bone marrow of EGFP rats into wild-type rats, the progeny of the transplanted marrow cells were tracked with a tag of EGFP. Recruitment of bone marrow-derived cells into glomeruli was dramatically facilitated in response to mesangiolysis evoked in anti-Thy1 antibody-mediated glomerulonephritis. In the restored glomeruli, 11% to 12% of glomerular cells were derived from the transplanted bone marrow. The number of bone marrow-derived CD45(+) cells transiently increased during the disease process, and CD45-negative cells constantly accounted for more than half of the bone marrow-derived population in glomeruli. Bone marrow-derived Thy1(+) cells kept increasing in number until the remodeling ceased and finally made up 7% to 8% of glomerular cells. Laser scanning microscopy displayed that the bone marrow-derived Thy1(+) cells provide structural support for glomerular capillaries, which indicates that they are mesangial cells. Although CD45(-)Thy1(-) bone marrow-derived cells exist during the remodeling of glomeruli, none of them expressed endothelial markers such as Factor VIII and RECA1 as long as they were tested. The results indicate that the bone marrow can give rise to mesangial cells in vivo.

Genetic analysis of endocytosis in Caenorhabditis elegans: coelomocyte uptake defective mutants

The coelomocytes of Caenorhabditis elegans are scavenger cells that continuously and nonspecifically endocytose fluid from the pseudocoelom (body cavity). Green fluorescent protein (GFP) secreted into the pseudocoelom from body wall muscle cells is endocytosed and degraded by coelomocytes. We show that toxin-mediated ablation of coelomocytes results in viable animals that fail to endocytose pseudocoelomic GFP, indicating that endocytosis by coelomocytes is not essential for growth or survival of C. elegans under normal laboratory conditions. We examined known viable endocytosis mutants, and performed RNAi for other known endocytosis genes, for coelomocyte uptake defective (Cup) phenotypes. We also screened for new genes involved in endocytosis by isolating viable mutants with Cup defects; this screen identified 14 different genes, many with multiple alleles. A variety of Cup terminal phenotypes were observed, consistent with defects at various steps in the endocytic pathway. Available molecular information indicates that the Cup mutant screen has identified novel components of the endocytosis machinery that are conserved in mammals but not in Saccharomyces cerevisiae, the only other organism for which large-scale genetic screens for endocytosis mutants have been performed.

A bright cyan-excitable orange fluorescent protein facilitates dual-emission microscopy and enhances bioluminescence imaging in vivo

Orange-red fluorescent proteins (FPs) are widely used in biomedical research for multiplexed epifluorescence microscopy with GFP-based probes, but their different excitation requirements make multiplexing with new advanced microscopy methods difficult. Separately, orange-red FPs are useful for deep-tissue imaging in mammals owing to the relative tissue transmissibility of orange-red light, but their dependence on illumination limits their sensitivity as reporters in deep tissues. Here we describe CyOFP1, a bright, engineered, orange-red FP that is excitable by cyan light. We show that CyOFP1 enables single-excitation multiplexed imaging with GFP-based probes in single-photon and two-photon microscopy, including time-lapse imaging in light-sheet systems. CyOFP1 also serves as an efficient acceptor for resonance energy transfer from the highly catalytic blue-emitting luciferase NanoLuc. An optimized fusion of CyOFP1 and NanoLuc, called Antares, functions as a highly sensitive bioluminescent reporter in vivo, producing substantially brighter signals from deep tissues than firefly luciferase and other bioluminescent proteins.

Fluid-phase uptake by macropinocytosis in Dictyostelium

To study fluid-phase endocytosis in living cells and its relationship to changes in the cell cortex, we have used a green fluorescent protein (GFP)-tagged version of coronin, an actin-associated protein that localises to dynamic regions of the Dictyostelium cell cortex. In the confocal microscope, internalisation of fluorescently labelled dextran as a fluid-phase marker can be recorded simultaneously with the recruitment of the coronin-GFP fusion-protein from the cytoplasm of the phagocyte. At crown-shaped surface protrusions, extracellular medium is taken up into vesicles with an average diameter of 1.6 microns, which is significantly larger than the 0.1 microns diameter of clathrin-coated pinosomes. The observed frequency of macropinosome formation can account for a large portion, if not all, of the fluid-phase uptake. The redistribution of coronin-GFP strongly resembles cytoskeletal rearrangements during phagocytosis. Scanning-electron micrographs indicate that crown-shaped cell-surface extensions can undergo shape changes, without a particle bound, that are similar to shape changes that occur during phagocytosis. In quantitative assays, the uptake of particles and fluid are about equally dependent on F-actin and coronin.

Regulation of presynaptic terminal organization by C. elegans RPM-1, a putative guanine nucleotide exchanger with a RING-H2 finger domain

Presynaptic terminals contain highly organized subcellular structures to facilitate neurotransmitter release. In C. elegans, the typical presynaptic terminal has an electron-dense active zone surrounded by synaptic vesicles. Loss-of-function mutations in the rpm-1 gene result in abnormally structured presynaptic terminals in GABAergic neuromuscular junctions (NMJs), most often manifested as a single presynaptic terminal containing multiple active zones. The RPM-1 protein has an RCC1-like guanine nucleotide exchange factor (GEF) domain and a RING-H2 finger. RPM-1 is most similar to the Drosophila presynaptic protein Highwire (HIW) and the mammalian Myc binding protein Pam. RPM-1 is localized to the presynaptic region independent of synaptic vesicles and functions cell autonomously. The temperature-sensitive period of rpm-1 coincides with the time of synaptogenesis. rpm-1 may regulate the spatial arrangement, or restrict the formation, of presynaptic structures.

Calcium-induced restructuring of nuclear envelope and endoplasmic reticulum calcium stores

The spatial organization of endoplasmic reticulum (ER) and nuclear envelope (NE) calcium stores is important for the regulation of localized calcium signals and sustained calcium gradients. Here, we have used a lumenal GFP fusion protein and shown that, in resting cells, large molecules can rapidly diffuse across the cell within the lumenal storage space defined by the ER and NE membranes. Increases in cytosolic calcium concentration reversibly fragmented ER tubules and prevented lumenal diffusion. However, the integrity of the NE was maintained, and a significant fraction of NE lumenal protein accumulated in an NE-associated vesicle. These dynamic properties of ER-NE calcium stores provide insights into the spatiotemporal control of calcium signaling.

Maturation and intranuclear transport of pre-ribosomes requires Noc proteins

How pre-ribosomes temporally and spatially mature during intranuclear biogenesis is not known. Here, we report three nucleolar proteins, Noc1p to Noc3p, that are required for ribosome maturation and transport. They can be isolated in two distinct complexes: Noc1p/Noc2p associates with 90S and 66S pre-ribosomes and is enriched in the nucleolus, and Noc2p/Noc3p associates with 66S pre-ribosomes and is mainly nucleoplasmic. Mutation of each Noc protein impairs intranuclear transport of 60S subunits at different stages and inhibits pre-rRNA processing. Overexpression of a conserved domain common to Noc1p and Noc3p is dominant-negative for cell growth, with a defect in nuclear 60S subunit transport, but no inhibition of pre-rRNA processing. We propose that the dynamic interaction of Noc proteins is crucial for intranuclear movement of ribosomal precursor particles, and, thereby represent a prerequisite for proper maturation.

Extracellular glycosaminoglycans modify cellular trafficking of lipoplexes and polyplexes

It has been shown that extracellular glycosaminoglycans (GAGs) limit the gene transfer by cationic lipids and polymers. The purpose of this study was to clarify how interactions with anionic GAGs (hyaluronic acid and heparan sulfate) modify the cellular uptake and distribution of lipoplexes and polyplexes. Experiments on cellular DNA uptake and GFP reporter gene expression showed that decreased gene expression can rarely be explained by lower cellular uptake. In most cases, the cellular uptake is not changed by GAG binding to the lipoplexes or polyplexes. Reporter gene expression is decreased or blocked by heparan sulfate, but it is increased by hyaluronic acid; this suggests that intracellular factors are involved. Confocal microscopy experiments demonstrated that extracellular heparan sulfate and hyaluronic acid are taken into cells both with free and DNA-associated carriers. We conclude that extracellular GAGs may alter both the cellular uptake and the intracellular behavior of the DNA complexes.

The nuclear envelope serves as an intermediary between the ER and Golgi complex in the intracellular parasite Toxoplasma gondii

Morphological examination of the highly polarized protozoan parasite Toxoplasma gondii suggests that secretory traffic in this organism progresses from the endoplasmic reticulum to the Golgi apparatus using the nuclear envelope as an intermediate compartment. While the endoplasmic reticulum is predominantly located near the basal end of the parasite, the Golgi is invariably adjacent to the apical end of the nucleus, and the space between the Golgi and nuclear envelope is filled with numerous coatomer-coated vesicles. Staining with antiserum raised against recombinant T. gondii beta-COP confirms its association with the apical juxtanuclear region. Perturbation of protein secretion using brefeldin A, microtubule inhibitors or dithiothreitol disrupts the Golgi, causing swelling of the nuclear envelope, particularly at its basal end. Prolonged drug treatment leads to gross distention of the endoplasmic reticulum, filling the basal end of the parasite. Cloning and sequencing of the T. gondii homolog of the chaperonin protein BiP identifies the carboxy-terminal amino acid sequence HDEL as this organism's endoplasmic reticulum-retention signal. Appending the HDEL motif to a recombinant secretory protein (a chimera between the parasite's major surface protein fusion, P30, and the Green Fluorescent Protein) causes this secretory reporter to be retained intracellularly. P30-GFP-HDEL fluorescence was most intense within the nuclear envelope, particularly at the apical end. These data support a model of secretion in which protein traffic from the endoplasmic reticulum to Golgi occurs via the apical end of the nuclear envelope.

GFP imaging: methodology and application to investigate cellular compartmentation in plants

The cloning of the jellyfish gfp (green fluorescent protein) gene and its alteration for expression in subcellular locations in transformed plant cells have resulted in new views of intracellular organization and dynamics. Fusions of GFP with entire proteins of known or unknown function have shown where the proteins are located and whether the proteins move from one compartment to another. GFP and variants with different spectral properties have been deliberately targeted to separate compartments to determine their size, shape, mobility, and dynamic changes during development or environmental response. Fluorescence Resonance Energy Transfer (FRET) between GFP variants can discern protein/ protein interactions. GFP has been used as a sensor to detect changes or differences in calcium, pH, voltage, metal, and enzyme activity. Photobleaching and photoactivation of GFP as well as fluorescence correlation spectroscopy can measure rates of diffusion and movement of GFP within or between compartments. This review covers past applications of these methods as well as promising developments in GFP imaging for understanding the functional organization of plant cells.

The dynamic organization of the perinucleolar compartment in the cell nucleus

The perinucleolar compartment (PNC) is a unique nuclear structure preferentially localized at the periphery of the nucleolus. Several small RNAs transcribed by RNA polymerase III (e.g., the Y RNAs, MRP RNA, and RNase P H1 RNA) and the polypyrimidine tract binding protein (PTB; hnRNP I) have thus far been identified in the PNC (Ghetti, A., S. PinolRoma, W.M. Michael, C. Morandi, and G. Dreyfuss. 1992. Nucleic Acids Res. 20:3671-3678; Matera, A.G., M.R. Frey, K. Margelot, and S.L. Wolin. 1995. J. Cell Biol. 129:1181-1193; Lee, B., A.G. Matera, D.C. Ward, and J. Craft. 1996. Proc. Natl. Acad. Sci. USA. 93: 11471-11476). In this report, we have further characterized this structure in both fixed and living cells. Detection of the PNC in a large number of human cancer and normal cells showed that PNCs are much more prevalent in cancer cells. Analysis through the cell cycle using immunolabeling with a monoclonal antibody, SH54, specifically recognizing PTB, demonstrated that the PNC dissociates at the beginning of mitosis and reforms at late telophase in the daughter nuclei. To visualize the PNC in living cells, a fusion protein between PTB and green fluorescent protein (GFP) was generated. Time lapse studies revealed that the size and shape of the PNC is dynamic over time. In addition, electron microscopic examination in optimally fixed cells revealed that the PNC is composed of multiple strands, each measuring approximately 80-180 nm diam. Some of the strands are in direct contact with the surface of the nucleolus. Furthermore, analysis of the sequence requirement for targeting PTB to the PNC using a series of deletion mutants of the GFP-PTB fusion protein showed that at least three RRMs at either the COOH or NH2 terminus are required for the fusion protein to be targeted to the PNC. This finding suggests that RNA binding may be necessary for PTB to be localized in the PNC.

Neuroprotection in the rat Parkinson model by intrastriatal GDNF gene transfer using a lentiviral vector

We used a recombinant lentiviral vector (rLV) for gene delivery of GDNF to the striatum, and assessed its neuroprotective effects in the intrastriatal 6-hydroxydopamine (6-OHDA) lesion model. The level of GDNF expression obtained with the rLV-GDNF vector was dose-related and ranged between 0.9-9.3 ng/mg tissue in the transduced striatum, as determined by ELISA, and 0.2-3.0 ng/mg tissue were detected in the ipsilateral substantia nigra (SN), due to anterograde transport of the GDNF protein. GDNF expression was apparent at 4 days and maintained for > 8 months after injection. Striatal delivery of rLV-GDNF efficiently protected the nigral dopamine (DA) neurons and their projection, against the 6-OHDA lesion (65-77% of intact side). Sprouting of the lesioned axons was observed along the nigrostriatal pathway, precisely corresponding to the areas containing anterogradely transported GDNF.

Visualization of IP(3) dynamics reveals a novel AMPA receptor-triggered IP(3) production pathway mediated by voltage-dependent Ca(2+) influx in Purkinje cells

IP(3) signaling in Purkinje cells is involved in the regulation of cell functions including LTD. We have used a GFP-tagged pleckstrin homology domain to visualize IP(3) dynamics in Purkinje cells. Surprisingly, IP(3) production was observed in response not only to mGluR activation, but also to AMPA receptor activation in Purkinje cells in culture. AMPA-induced IP(3) production was mediated by depolarization-induced Ca(2+) influx because it was mimicked by depolarization and was blocked by inhibition of the P-type Ca(2+) channel. Furthermore, trains of complex spikes, elicited by climbing fiber stimulation (1 Hz), induced IP(3) production in Purkinje cells in cerebellar slices. These results revealed a novel IP(3) signaling pathway in Purkinje cells that can be elicited by synaptic inputs from climbing fibers.

Live Cell Imaging of ERK and MEK: simple binding equilibrium explains the regulated nucleocytoplasmic distribution of ERK

In response to epidermal growth factor (EGF), the mitogen-activated protein kinase ERK2 translocates into the nucleus. To probe the mechanisms regulating the subcellular localization of ERK2, we used live cell imaging to examine the interaction between MEK1 and ERK2. Fluorescence resonance energy transfer (FRET) studies show that MEK1 and ERK2 directly interact and demonstrate that this interaction in the cytoplasm is largely responsible for cytoplasmic retention of ERK2. Stimulation with EGF caused loss of FRET as ERK separated from MEK and moved into the nucleus. FRET was recovered as ERK returned to the cytosol, indicating ERK reassociation with MEK in the cytoplasm. The EGF-induced transit of ERK through the nucleus was complete within 20 min, and there was no significant movement of MEK into the nucleus. Fluorescence recovery after photobleaching experiments was used to assess the rate of movement of MEK and ERK. The steady-state rate of ERK entry into the nucleus in resting cells was energy-independent and greater than the rate of ERK entry upon EGF stimulation. This suggests that the rate constant for ERK transport across the nuclear membrane is not limiting nuclear entry. Thus, we suggest that the movement of ERK into and out of the nucleus in response to agonist occurs primarily by diffusion and is controlled by interactions with binding partners in the cytosol and nucleus. No evidence of ERK dimerization was detected by FRET methods; the kinetics for nucleocytoplasmic transport were unaffected by mutations in the ERK putative dimerization domain.

Applications of novel resonance energy transfer techniques to study dynamic hormone receptor interactions in living cells

Many aspects of hormone receptor function that are crucial for controlling signal transduction of endocrine pathways can be monitored more accurately with the use of non-invasive, live cell resonance energy transfer (RET) techniques. Fluorescent RET (FRET), and its variation, bioluminescent RET (BRET), can be used to assess the real-time responses to specific hormonal stimuli, whilst preserving the cellular protein network, compartmentalization and spatial arrangement. Both FRET and BRET can be readily adapted to the study of membrane proteins. Here, we focus on their applications to the analysis of interactions involving the superfamily of hormone G-protein-coupled receptors. RET is also emerging as a significant tool for the determination of protein function in general. Such techniques will undoubtedly be of value in determining the functional identities of the vast array of proteins that are encoded by the human genome.

The dynamics of SAP90/PSD-95 recruitment to new synaptic junctions

SAP90/PSD-95 is thought to be a central organizer of the glutamatergic synapse postsynaptic reception apparatus. To assess its potential role during glutamatergic synapse formation, we used GFP-tagged SAP90/PSD-95, time lapse confocal microscopy, and cultured hippocampal neurons to determine its dynamic recruitment into new synaptic junctions. We report that new SAP90/PSD-95 clusters first appeared at new axodendritic contact sites within 20-60 min of contact establishment. SAP90/PSD-95 clustering was rapid, with kinetics that fit a single exponential with a mean time constant of approximately 23 min. Most new SAP90/PSD-95 clusters were found juxtaposed to functional presynaptic boutons as determined by labeling with FM 4-64. No evidence was found for the existence of discrete transport particles similar to those previously reported to mediate presynaptic active zone cytoskeleton assembly. Instead, we found that SAP90/PSD-95 is recruited to nascent synapses from a diffuse dendritic cytoplasmic pool. Our findings show that SAP90/PSD-95 is recruited to nascent synaptic junctions early during the assembly process and indicate that its assimilation is fundamentally different from that of presynaptic active zone components.

Real-time imaging of nuclear permeation by EGFP in single intact cells

The NPC is the portal for the exchange of proteins, mRNA, and ions between nucleus and cytoplasm. Many small molecules (<10 kDa) permeate the nucleus by simple diffusion through the pore, but molecules larger than 70 kDa require ATP and a nuclear localization sequence for their transport. In isolated Xenopus oocyte nuclei, diffusion of intermediate-sized molecules appears to be regulated by the NPC, dependent upon [Ca(2+)] in the nuclear envelope. We have applied real-time imaging and fluorescence recovery after photobleaching to examine the nuclear pore permeability of 27-kDa EGFP in single intact cells. We found that EGFP diffused bidirectionally via the NPC across the nuclear envelope. Although diffusion is slowed approximately 100-fold at the nuclear envelope boundary compared to diffusion within the nucleus or cytoplasm, this delay is expected for the reduced cross-sectional area of the NPCs. We found no evidence for significant nuclear pore gating or block of EGFP diffusion by depletion of perinuclear Ca(2+) stores, as assayed by a nuclear cisterna-targeted Ca(2+) indicator. We also found that EGFP exchange was not altered significantly during the cell cycle.

Glial cell death induced by overexpression of alpha-synuclein

alpha-Synuclein is present in intracellular protein aggregates that are hallmarks of common neurodegenerative disorders including Parkinson disease, dementia with Lewy bodies, and multiple system atrophy. alpha-Synuclein is localized in neurons and presynaptic terminals. Under pathological conditions, however, it is also found in glia. The role of alpha-synuclein in glial cells and its relevance to the molecular pathology of neurodegenerative diseases is presently unclear. To investigate the consequence of alpha-synuclein overexpression in glia, we transfected U373 astrocytoma cells with vectors encoding wild-type human alpha-synuclein or C-terminally truncated synuclein fused to red fluorescent protein. alpha-synuclein immunocytochemistry of transfected astroglial cells revealed diffuse cytoplasmic labeling associated with discrete inclusions both within cell bodies and processes. Susceptibility to oxidative stress was increased in astroglial cells overexpressing alpha-synuclein, particularly in the presence of cytoplasmic inclusions. Furthermore, overexpression of alpha-synuclein induced apoptotic death of astroglial cells as shown by TUNEL staining. Our in vitro model is the first to replicate salient features of the glial pathology associated with alpha-synucleinopathies. It provides a simple testbed to further explore the cascade of events that leads to apoptotic glial cell death in some of these disorders; it may also be useful to assess the effects of therapeutic interventions including antioxidative and antiapoptotic strategies.

Mitochondrial activity and forward scatter vary in necrotic, apoptotic and membrane-intact spermatozoan subpopulations

In the present study, we have related mitochondrial membrane potential (DeltaPsim) and forward scatter (FSC) to apoptotic-related changes in spermatozoa. Thawed red deer spermatozoa were incubated in synthetic oviductal fluid medium (37 degrees C, 5% CO2), with or without antioxidant (100 microm Trolox). At 0, 3, 6 and 9 h, aliquots were assessed for motility and were stained with a combination of Hoechst 33342, propidium ioide (PI), YO-PRO-1 and Mitotracker Deep Red for flow cytometry. The proportion of spermatozoa YO-PRO-1+ and PI+ (indicating a damaged plasmalemma; DEAD) increased, whereas that of YO-PRO-1- and PI- (INTACT) spermatozoa decreased. The proportion of YO-PRO-1+ and PI- spermatozoa (altered plasmalemma; APOPTOTIC) did not change. Both DEAD and APOPTOTIC spermatozoa had low DeltaPsim. Most high-DeltaPsim spermatozoa were INTACT, and their proportion decreased with time. The FSC signal also differed between different groups of spermatozoa, in the order APOPTOTIC > DEAD > INTACT/low DeltaPsim > INTACT/high DeltaPsim; however, the actual meaning of this difference is not clear. APOPTOTIC spermatozoa seemed motile at 0 h, but lost motility with time. Trolox only slightly improved the percentage of INTACT spermatozoa (P < 0.05). The population of APOPTOTIC spermatozoa in the present study may be dying cells, possibly with activated cell death pathways (loss of DeltaPsim). We propose that the sequence of spermatozoon death here would be: (1) loss of DeltaPsim; (2) membrane changes (YO-PRO-1+ and PI-); and (3) membrane damage (PI+). INTACT spermatozoa with low DeltaPsim or altered FSC may be compromised cells. The present study is the first that directly relates membrane integrity, apoptotic markers and mitochondrial status in spermatozoa. The results of the present study may help us understand the mechanisms leading to loss of spermatozoon viability after thawing.

Targeted Subcellular Protein Delivery Using Cleavable Cyclic Cell-Penetrating Peptides

The delivery of entire functional proteins into living cells is a long-sought goal in science. Cyclic cell-penetrating peptides (cCPPs) have proven themselves to be potent delivery vehicles to carry proteins upon conjugation into the cytosol of living cells with immediate bioavailability via a non-endosomal uptake pathway. With this strategy, we pursue the cytosolic delivery of mCherry, a medium-sized fluorescent protein. Afterward, we achieve subcellular delivery of mCherry to different intracellular loci by genetic fusion of targeting peptides to the protein sequence. We show efficient transport into a membrane-bound compartment, the nucleus, as well as targeting of the actin cytoskeleton, marking one of the first ways to label actin fluorescently in genetically unmodified living cells. Furthermore, we demonstrate that only by conjugation of cCPPs via a disulfide bond, is flawless localization to the target area achieved. This finding underlines the importance of using a cCPP-based delivery vehicle that is cleaved inside cells, for the precise intracellular localization of a protein of interest.