Four-dimensional imaging and quantitative reconstruction to analyse complex spatiotemporal processes in live cells.

Live-cell imaging technology using fluorescent proteins (green fluorescent protein and its homologues) has revolutionized the study of cellular dynamics. But tools that can quantitatively analyse complex spatiotemporal processes in live cells remain lacking. Here we describe a new technique--fast multi-colour four-dimensional imaging combined with automated and quantitative time-space reconstruction--to fill this gap. As a proof of principle, we apply this method to study the re-formation of the nuclear envelope in live cells. Four-dimensional imaging of three spectrally distinct fluorescent proteins is used to simultaneously visualize three different cellular compartments at high speed and with high spatial resolution. The highly complex data, comprising several thousand images from a single cell, were quantitatively reconstructed in time-space by software developed in-house. This analysis reveals quantitative and qualitative insights into the highly ordered topology of nuclear envelope formation, in correlation with chromatin expansion - results that would have been impossible to achieve by manual inspection alone. Our new technique will greatly facilitate study of the highly ordered dynamic architecture of eukaryotic cells.

Dynamics and retention of misfolded proteins in native ER membranes.

When co-translationally inserted into endoplasmic reticulum (ER) membranes, newly synthesized proteins encounter the lumenal environment of the ER, which contains chaperone proteins that facilitate the folding reactions necessary for protein oligomerization, maturation and export from the ER. Here we show, using a temperature-sensitive variant of vesicular stomatitis virus G protein tagged with green fluorescent protein (VSVG-GFP), and fluorescence recovery after photobleaching (FRAP), the dynamics of association of folded and misfolded VSVG complexes with ER chaperones. We also investigate the potential mechanisms underlying protein retention in the ER. Misfolded VSVG-GFP complexes at 40 degrees C are highly mobile in ER membranes and do not reside in post-ER compartments, indicating that they are not retained in the ER by immobilization or retrieval mechanisms. These complexes are immobilized in ATP-depleted or tunicamycin-treated cells, in which VSVG-chaperone interactions are no longer dynamic. These results provide insight into the mechanisms of protein retention in the ER and the dynamics of protein-folding complexes in native ER membranes.

Dual-colour imaging with GFP variants.

Green fluorescent protein (GFP) has become an important tool in cell biology and is widely used as a reporter for imaging intracellular proteins and structures in live cells. Recently, spectral variants of GFP with red- and blue-shifted fluorescence emissions have been characterized, opening the possibility of double labelling with two different-coloured GFP fusion proteins. This article reviews recent advances in this technique, with special emphasis on time-lapse imaging applications in living cells.

Retrograde transport of Golgi-localized proteins to the ER.

The ER is uniquely enriched in chaperones and folding enzymes that facilitate folding and unfolding reactions and ensure that only correctly folded and assembled proteins leave this compartment. Here we address the extent to which proteins that leave the ER and localize to distal sites in the secretory pathway are able to return to the ER folding environment during their lifetime. Retrieval of proteins back to the ER was studied using an assay based on the capacity of the ER to retain misfolded proteins. The lumenal domain of the temperature-sensitive viral glycoprotein VSVGtsO45 was fused to Golgi or plasma membrane targeting domains. At the nonpermissive temperature, newly synthesized fusion proteins misfolded and were retained in the ER, indicating the VSVGtsO45 ectodomain was sufficient for their retention within the ER. At the permissive temperature, the fusion proteins were correctly delivered to the Golgi complex or plasma membrane, indicating the lumenal epitope of VSVGtsO45 also did not interfere with proper targeting of these molecules. Strikingly, Golgi-localized fusion proteins, but not VSVGtsO45 itself, were found to redistribute back to the ER upon a shift to the nonpermissive temperature, where they misfolded and were retained. This occurred over a time period of 15 min-2 h depending on the chimera, and did not require new protein synthesis. Significantly, recycling did not appear to be induced by misfolding of the chimeras within the Golgi complex. This suggested these proteins normally cycle between the Golgi and ER, and while passing through the ER at 40 degrees C become misfolded and retained. The attachment of the thermosensitive VSVGtsO45 lumenal domain to proteins promises to be a useful tool for studying the molecular mechanisms and specificity of retrograde traffic to the ER.

Nuclear pore complexes form immobile networks and have a very low turnover in live mammalian cells.

The nuclear pore complex (NPC) and its relationship to the nuclear envelope (NE) was characterized in living cells using POM121-green fluorescent protein (GFP) and GFP-Nup153, and GFP-lamin B1. No independent movement of single pore complexes was found within the plane of the NE in interphase. Only large arrays of NPCs moved slowly and synchronously during global changes in nuclear shape, strongly suggesting mechanical connections which form an NPC network. The nuclear lamina exhibited identical movements. NPC turnover measured by fluorescence recovery after photobleaching of POM121 was less than once per cell cycle. Nup153 association with NPCs was dynamic and turnover of this nucleoporin was three orders of magnitude faster. Overexpression of both nucleoporins induced the formation of annulate lamellae (AL) in the endoplasmic reticulum (ER). Turnover of AL pore complexes was much higher than in the NE (once every 2.5 min). During mitosis, POM121 and Nup153 were completely dispersed and mobile in the ER (POM121) or cytosol (Nup153) in metaphase, and rapidly redistributed to an immobilized pool around chromatin in late anaphase. Assembly and immobilization of both nucleoporins occurred before detectable recruitment of lamin B1, which is thus unlikely to mediate initiation of NPC assembly at the end of mitosis.

Nuclear membrane dynamics and reassembly in living cells: targeting of an inner nuclear membrane protein in interphase and mitosis.

The mechanisms of localization and retention of membrane proteins in the inner nuclear membrane and the fate of this membrane system during mitosis were studied in living cells using the inner nuclear membrane protein, lamin B receptor, fused to green fluorescent protein (LBR-GFP). Photobleaching techniques revealed the majority of LBR-GFP to be completely immobilized in the nuclear envelope (NE) of interphase cells, suggesting a tight binding to heterochromatin and/or lamins. A subpopulation of LBR-GFP within ER membranes, by contrast, was entirely mobile and diffused rapidly and freely (D = 0. 41 +/- 0.1 microm2/s). High resolution confocal time-lapse imaging in mitotic cells revealed LBR-GFP redistributing into the interconnected ER membrane system in prometaphase, exhibiting the same high mobility and diffusion constant as observed in interphase ER membranes. LBR-GFP rapidly diffused across the cell within the membrane network defined by the ER, suggesting the integrity of the ER was maintained in mitosis, with little or no fragmentation and vesiculation. At the end of mitosis, nuclear membrane reformation coincided with immobilization of LBR-GFP in ER elements at contact sites with chromatin. LBR-GFP-containing ER membranes then wrapped around chromatin over the course of 2-3 min, quickly and efficiently compartmentalizing nuclear material. Expansion of the NE followed over the course of 30-80 min. Thus, selective changes in lateral mobility of LBR-GFP within the ER/NE membrane system form the basis for its localization to the inner nuclear membrane during interphase. Such changes, rather than vesiculation mechanisms, also underlie the redistribution of this molecule during NE disassembly and reformation in mitosis.

Kinetic analysis of secretory protein traffic and characterization of golgi to plasma membrane transport intermediates in living cells.

Quantitative time-lapse imaging data of single cells expressing the transmembrane protein, vesicular stomatitis virus ts045 G protein fused to green fluorescent protein (VSVG-GFP), were used for kinetic modeling of protein traffic through the various compartments of the secretory pathway. A series of first order rate laws was sufficient to accurately describe VSVG-GFP transport, and provided compartment residence times and rate constants for transport into and out of the Golgi complex and delivery to the plasma membrane. For ER to Golgi transport the mean rate constant (i.e., the fraction of VSVG-GFP moved per unit of time) was 2.8% per min, for Golgi to plasma membrane transport it was 3.0% per min, and for transport from the plasma membrane to a degradative site it was 0.25% per min. Because these rate constants did not change as the concentration of VSVG-GFP in different compartments went from high (early in the experiment) to low (late in the experiment), secretory transport machinery was never saturated during the experiments. The processes of budding, translocation, and fusion of post-Golgi transport intermediates carrying VSVG- GFP to the plasma membrane were also analyzed using quantitative imaging techniques. Large pleiomorphic tubular structures, rather than small vesicles, were found to be the primary vehicles for Golgi to plasma membrane transport of VSVG-GFP. These structures budded as entire domains from the Golgi complex and underwent dynamic shape changes as they moved along microtubule tracks to the cell periphery. They carried up to 10,000 VSVG-GFP molecules and had a mean life time in COS cells of 3.8 min. In addition, they fused with the plasma membrane without intersecting other membrane transport pathways in the cell. These properties suggest that the post-Golgi intermediates represent a unique transport organelle for conveying large quantities of protein cargo from the Golgi complex directly to the plasma membrane.

ZAP-70 association with T cell receptor zeta (TCRzeta): fluorescence imaging of dynamic changes upon cellular stimulation.

The nonreceptor protein tyrosine kinase ZAP-70 is a critical enzyme required for successful T lymphocyte activation. After antigenic stimulation, ZAP-70 rapidly associates with T cell receptor (TCR) subunits. The kinetics of its translocation to the cell surface, the properties of its specific interaction with the TCRzeta chain expressed as a chimeric protein (TTzeta and Tzetazeta), and its mobility in different intracellular compartments were studied in individual live HeLa cells, using ZAP-70 and Tzetazeta fused to green fluorescent protein (ZAP-70 GFP and Tzetazeta-GFP, respectively). Time-lapse imaging using confocal microscopy indicated that the activation-induced redistribution of ZAP-70 to the plasma membrane, after a delayed onset, is of long duration. The presence of the TCRzeta chain is critical for the redistribution, which is enhanced when an active form of the protein tyrosine kinase Lck is coexpressed. Binding specificity to TTzeta was indicated using mutant ZAP-70 GFPs and a truncated zeta chimera. Photobleaching techniques revealed that ZAP-70 GFP has decreased mobility at the plasma membrane, in contrast to its rapid mobility in the cytosol and nucleus. Tzetazeta- GFP is relatively immobile, while peripherally located ZAP-70 in stimulated cells is less mobile than cytosolic ZAP-70 in unstimulated cells, a phenotype confirmed by determining the respective diffusion constants. Examination of the specific molecular association of signaling proteins using these approaches has provided new insights into the TCRzeta-ZAP-70 interaction and will be a powerful tool for continuing studies of lymphocyte activation.

An evolutionarily conserved NPC subcomplex, which redistributes in part to kinetochores in mammalian cells.

The nuclear pore complexes (NPCs) are evolutionarily conserved assemblies that allow traffic between the cytoplasm and the nucleus. In this study, we have identified and characterized a novel human nuclear pore protein, hNup133, through its homology with the Saccharomyces cerevisiae nucleoporin scNup133. Two-hybrid screens and immunoprecipitation experiments revealed a direct and evolutionarily conserved interaction between Nup133 and Nup84/Nup107 and indicated that hNup133 and hNup107 are part of a NPC subcomplex that contains two other nucleoporins (the previously characterized hNup96 and a novel nucleoporin designated as hNup120) homologous to constituents of the scNup84 subcomplex. We further demonstrate that hNup133 and hNup107 are localized on both sides of the NPC to which they are stably associated at interphase, remain associated as part of a NPC subcomplex during mitosis, and are targeted at early stages to the reforming nuclear envelope. Throughout mitosis, a fraction of hNup133 and hNup107 localizes to the kinetochores, thus revealing an unexpected connection between structural NPCs constituents and kinetochores. Photobleaching experiments further showed that the mitotic cytoplasm contains kinetochore-binding competent hNup133 molecules and that in contrast to its stable association with the NPCs the interaction of this nucleoporin with kinetochores is dynamic.

Nucleocytoplasmic transport: diffusion channel or phase transition?

How exactly large molecules translocate through nuclear pores has been mysterious for a long time. Recent kinetic measurements of transport rates through the pore have led to a novel translocation model that elegantly combines selectivity with very high transport rates.

A bromodomain protein, MCAP, associates with mitotic chromosomes and affects G(2)-to-M transition.

We describe a novel nuclear factor called mitotic chromosome-associated protein (MCAP), which belongs to the poorly understood BET subgroup of the bromodomain superfamily. Expression of the 200-kDa MCAP was linked to cell division, as it was induced by growth stimulation and repressed by growth inhibition. The most notable feature of MCAP was its association with chromosomes during mitosis, observed at a time when the majority of nuclear regulatory factors were released into the cytoplasm, coinciding with global cessation of transcription. Indicative of its predominant interaction with euchromatin, MCAP localized on mitotic chromosomes with exquisite specificity: (i) MCAP-chromosome association became evident subsequent to the initiation of histone H3 phosphorylation and early chromosomal condensation; and (ii) MCAP was absent from centromeres, the sites of heterochromatin. Supporting a role for MCAP in G(2)/M transition, microinjection of anti-MCAP antibody into HeLa cell nuclei completely inhibited the entry into mitosis, without abrogating the ongoing DNA replication. These results suggest that MCAP plays a role in a process governing chromosomal dynamics during mitosis.

A new model for nuclear envelope breakdown.

Nuclear envelope breakdown was investigated during meiotic maturation of starfish oocytes. Fluorescent 70-kDa dextran entry, as monitored by confocal microscopy, consists of two phases, a slow uniform increase and then a massive wave. From quantitative analysis of the first phase of dextran entry, and from imaging of green fluorescent protein chimeras, we conclude that nuclear pore disassembly begins several minutes before nuclear envelope breakdown. The best fit for the second phase of entry is with a spreading disruption of the membrane permeability barrier determined by three-dimensional computer simulations of diffusion. We propose a new model for the mechanism of nuclear envelope breakdown in which disassembly of the nuclear pores leads to a fenestration of the nuclear envelope double membrane.

A preliminary report on investigation of oncogenic potential of herpes simplex virus type 2 in Cebus monkeys.

A total of 301 female and 133 male Cebus monkeys have been placed under study during a 3-year period. Females are inoculated intradermally into the cervix every 6 months; 225 receive virus and 76 receive control material. More than 50% of the animals were infected on primary inoculation, and a similar percentage was foundon the 1st reinoculation. Males are housed with females at 1:1 to 1:3 ratios. Eighteen % of the males exposed to virus-inoculated females have become infected. To date, a total of 55 pregnancies have produced 14 live births and 8 abortions. The remaining 33 animals are still pregnant. No neonatal herpes simplex virus type 2 infections have been identified. Cytological changes of mild (atypia) to moderate (dysplasia) anaplasia have persisted for 12 to 32 months in 13 herpes simplex virus type 2-infected females. These animals received their 1st inoculation 14 to 50 months ago. Persistent anaplasia has not been found in control animals.

Nutritional studies in the pregnant rhesus monkey--the effect of protein-calorie or protein deprivation on growth of the fetal brain.

Twenty four pregnant nulliparous rhesus monkeys were distributed in three groups. While pregnant, the mothers were fed a diet, adequate in mineral and vitamins, that afforded 4.2 g protein and 100 cal; 1.2 g protein and 100 cal; or 1.2 g protein and 50 cal per kg per day. The fetuses were taken by cesarian section at 156 days gestation (term = 165 days) and the cerebrum and cerebellum were subsequently analysed chemically to assess composition and growth. Analyses revealed no statistically significant changes in protein, DNA, RNA, cholesterol, phospholipid, water, or chloride space of either tissue. The zinc concentration per gram of cerebral tissue or protein was significantly elevated in the low protein low calorie group. These results indicate that the brain of the fetus of this primate is protected during frank protein-calorie restriction of the mother. Moreover it is during this time that the major part of brain development takes place. It is argued that the differences observed after maternal restriction of protein and/or calories in subprimate mammals are not necessarily applicable to the human situation.

Febrile seizures and later intellectual performance.

The relationship of febrile seizures to later intellectual and academic performance was examined in a sibling-control study. Amont 431 sibling pairs tested at the age of 7 years, the mean full scale IQ on the Vechsler Intelligence Scales for Children was not different for children who had febrile seizures as compared with siblings who were seizure-free. Neither recurrent seizures nor those lasting 30 minutes or longer were associated with IQ deficit. Poor academic achievement, defined as Wide Range Achievement Test performance more than one grade level below school placement in children with IQs of 90 or above, was equally frequent in index cases and control patients. Febrile seizures were not associated with a decrement in IQ or early academic performance, as judged by comparison of affected children with their siblings.

Posttraumatic Amnesia as a predictor of outcome after severe closed head injury. Prospective assessment.

OBJECTIVES: To identify the demographic and clinical variables related to the duration of posttraumatic amnesia after severe closed head injury; to evaluate the usefulness of posttraumatic amnesia duration in predicting outcome at the time of hospital discharge and at 6 months after injury. SETTING: Four clinical centers located in primary care hospitals. PATIENTS: Three hundred fourteen severely injured subjects aged 16 years or older who did not have trauma as a result of a penetrating injury and came out of coma before hospital discharge. INTERVENTIONS: Approximately half of the subjects were administered phenytoin sodium for some period after termination of coma; 17% were administered dexamethasone and 41% morphine sulfate. MAIN OUTCOME MEASURES: Galveston Orientation and Amnesia Test scores defined the duration of posttraumatic amnesia. The Glasgow Outcome Scale was used to grade outcome at the time of hospital discharge and at 6 months. RESULTS: Older age, low initial Glasgow Coma Scale score, nonreactive pupil(s), coma duration, and use of phenytoin were associated with a longer duration of posttraumatic amnesia. Poor pupillary response, time in coma, and duration of posttraumatic amnesia and use of phenytoin was predictive of the 6-month outcome. CONCLUSIONS: The results support the prognostic usefulness of prospectively measuring duration of posttraumatic amnesia after termination of coma. Pending replication, our findings suggest that posttraumatic amnesia duration may be a useful surrogate outcome measure for clinical trials involving interventions for acute head injury.

Migraine and other diseases in women of reproductive age. The influence of smoking on observed associations.

From among the pregnant women in the Collaborative Perinatal Project of the National Institute of Neurological and Communicative Disorders and Stroke, we identified 508 who had migraine, and 3192 who had no history of migraine, of taking headache medication during the previous 12 months, and of headaches during the pregnancy. Migraineurs smoked more heavily and had a longer smoking history than their headache-free peers. Among migraineurs, smokers were not more likely to consume analgesics than nonsmokers. Regardless of smoking classification, more migraineurs consumed tranquilizers, amphetamines, and sleeping pills than headache-free women. Among smokers only, migraine was associated with heart disease, thrombosis/phlebitis, asthma, peptic ulcer, and pneumonia. In nonsmokers, migraine was associated with drug sensitivity and other allergies.

Preclinical detection in studies of the etiology, natural history, and treatment of Parkinson's disease.

The development of reliable preclinical detection procedures for idiopathic Parkinson's disease may be the fundamental advance required for the establishment of the cause, the natural history, and ultimately, the prevention of this neurodegenerative disorder. The usefulness of these preclinical markers in efforts to better understand the etiology and development of this disorder will relate to whether they are direct measures of dopamine production or indirect measures such as metabolic changes or comorbidity, whether they can be used in the first or later decades of life, whether they are invasive, and whether they are expensive and sophisticated or simple and cheap. An overview of the criteria for evaluation of the utility of specific markers, as well as an assessment of the importance of early markers in future research, is presented.

Maternal seizure disorder, outcome of pregnancy, and neurologic abnormalities in the children.

Among 45,000 pregnant women, 21.4 per 1000 (2.1%) reported at least one seizure before or during pregnancy. During the study pregnancy, 4.4 per 1000 had a noneclamptic seizure, and another 4.5 per 1000 had one in the 5 years preceding the study. Stillbirth, microcephaly, mental retardation, and nonfebrile seizure disorders occurred with heightened frequency in the offspring of women with seizure disorders; low birthweight, neonatal seizures, and first-year deaths were not more common. Approximately 80% of the women with seizure disorders had infants with none of the unfavorable outcomes studied. The observational nature of this and other clinical studies on this topic makes it difficult to evaluate the role of medical therapy in the outcome.

The risk of recurrence of nonfebrile seizures in children.

In a prospective study, the risk of recurrence after a first postneonatal nonfebrile seizure was 61% by age 7 years. The risk of recurrence for nonsymptomatic seizures was considerably higher than for seizures attributed to immediate precipitating factors. Focal motor seizures were more likely than generalized motor seizures to recur. Children who had prior neonatal seizures were at greater risk for nonfebrile recurrence than children with no prior seizure. Family history and neurodevelopmental status were not significantly related to recurrence risk. Almost 90% of recurrences took place within 1 year, and 96% within 2 years.