The development of cloning vectors for green fluorescent protein (GFP) and the simplicity of yeast reverse genetics allow straightforward labeling of yeast proteins in living cells. Budding and fission yeast are therefore attractive organisms in which to study dynamic cellular processes such as growth, cell division, and morphogenesis using live cell fluorescence microscopy. This article focuses on methods to culture, mount, and observe budding yeast cells using three-dimensional (3D) microscopy, but the methods are broadly applicable to other types of cells and other imaging techniques. The emphasis is on 3D imaging, because yeast cells are roughly spherical, and most organelles in yeast move in three dimensions. Three-dimensional imaging also makes it possible to apply image restoration methods (e.g., deconvolution) to obtain sharper images with better definition. This is important, because yeast cells are small (haploid Saccharomyces cerevisiae cells have a diameter of ~4-5 µm) relative to the resolution of even the best optical microscope (~0.25 µm).

The development of cloning vectors for green fluorescent protein (GFP) and the simplicity of yeast reverse genetics allow straightforward labeling of yeast proteins in living cells. Budding and fission yeast are therefore attractive organisms in which to study dynamic cellular processes such as growth, cell division, and morphogenesis using live cell fluorescence microscopy. This article focuses on methods to culture, mount, and observe budding yeast cells using three-dimensional (3D) microscopy, but themethods are broadly applicable to other types of cells and other imaging techniques. The emphasis is on 3D imaging, because yeast cells are roughly spherical, andmost organelles in yeast move in three dimensions. Three-dimensional imaging also makes it possible to apply image restorationmethods (e.g., deconvolution) to obtain sharper images with better definition. This is important, because yeast cells are small (haploid Saccharomyces cerevisiae cells have a diameter of ~4–5 μm) relative to the resolution of even the best optical microscope (~0.25 μm).

Many proteins or other biological macromolecules are localized to more than one subcellular structure. The fraction of a protein in different cellular compartments is often measured by colocalization with organelle-specific fluorescent markers, requiring availability of fluorescent probes for each compartment and acquisition of images for each in conjunction with the macromolecule of interest. Alternatively, tailored algorithms allow finding particular regions in images and quantifying the amount of fluorescence they contain. Unfortunately, this approach requires extensive hand-tuning of algorithms and is often cell type-dependent. Here we describe a machine-learning approach for estimating the amount of fluorescent signal in different subcellular compartments without hand tuning, requiring only the acquisition of separate training images of markers for each compartment. In testing on images of cells stained with mixtures of probes for different organelles, we achieved a 93% correlation between estimated and expected amounts of probes in each compartment. We also demonstrated that the method can be used to quantify drug-dependent protein translocations. The method enables automated and unbiased determination of the distributions of protein across cellular compartments, and will significantly improve imaging-based high-throughput assays and facilitate proteome-scale localization efforts.

Glioblastoma multiforme (GBM) is a highly aggressive form of brain cancer associated with a very poor prognosis. Recently, the initiation and growth of GBM has been linked to brain tumor-initiating cells (BTICs), which are poorly differentiated and share features with neural stem cells (NSCs). Here we describe a kinome-wide RNA interference screen to identify factors that control the tumorigenicity of BTICs. We identified several genes whose silencing induces differentiation of BTICs derived from multiple GBM patients. In particular, knockdown of the adaptor protein TRRAP significantly increased differentiation of cultured BTICs, sensitized the cells to apoptotic stimuli, and negatively affected cell cycle progression. TRRAP knockdown also significantly suppressed tumor formation upon intracranial BTIC implantation into mice. Together, these findings support a critical role for TRRAP in maintaining a tumorigenic, stem cell-like state.

BACKGROUND:The mitotic spindle is a complex mechanical apparatus required for accurate segregation of sister chromosomes during mitosis. We designed a genetic screen using automated microscopy to discover factors essential for mitotic progression. Using a RNA interference library of 49,164 double-stranded RNAs targeting 23,835 human genes, we performed a loss of function screen to look for small interfering RNAs that arrest cells in metaphase.RESULTS:Here we report the identification of genes that, when suppressed, result in structural defects in the mitotic spindle leading to bent, twisted, monopolar, or multipolar spindles, and cause cell cycle arrest. We further describe a novel analysis methodology for large-scale RNA interference datasets that relies on supervised clustering of these genes based on Gene Ontology, protein families, tissue expression, and protein-protein interactions.CONCLUSION:This approach was utilized to classify functionally the identified genes in discrete mitotic processes. We confirmed the identity for a subset of these genes and examined more closely their mechanical role in spindle architecture.

I kappa B kinase 2 (IKK2 or IKK beta) is a component of the IKK complex that coordinates the cellular response to a diverse set of extracellular stimuli, including cytokines, microbial infection, and stress. In response to an external stimulus, the complex is activated, resulting in the phosphorylation and subsequent proteasome-mediated degradation Of I kappa B proteins. This event triggers the nuclear import of the NF-kappa B transcription factor, which activates the transcription of genes that regulate a variety of fundamental biological processes, including immune response, cell survival, and development. Here, we define an essential role for IKK2 in normal mitotic progression and the maintenance of spindle bipolarity. Chemical and genetic perturbation of IKK2 promotes the formation of multipolar spindles and chromosome missegregation. Depletion of IKK2 results in the deregulation of Aurora A protein stability and coincident hyperactivation of a putative Aurora A substrate, the mitotic motor KIF11. These data support a function for IKK2 as an antagonist of Aurora A signaling during mitosis. Additionally, our results indicate a direct role for IKK2 in the maintenance of genome stability and underscore the potential for oncogenic consequences in targeting this kinase for therapeutic intervention.

As cells enter mitosis, centrosomes dramatically increase in size and ability to nucleate microtubules. This process, termed centrosome maturation, is driven by the accumulation and activation of gamma-tubulin and other proteins that form the pericentriolar material on centrosomes during G2/prophase. Here, we show that the human centrosomal protein, Cep192 (centrosomal protein of 192 kDa), is an essential component of the maturation machinery. Specifically, we havefound that siRNA depletion of Cep192 results in a complete loss of functional centrosomes in mitotic but not interphase cells. In mitotic cells lacking Cep192, microtubules become organized around chromosomes but rarely acquire stable bipolar configurations. These cells contain normal numbers of centrioles but cannot assemble gamma-tubulin, pericentrin, or other pericentriolar proteins into an organized PCM. Alternatively, overexpression of Cep 192 results in the formation of multiple, extracentriolar foci of gamma-tubulin and pericentrin. Together, our findings support the hypothesis that Cep192 stimulates the formation of the scaffolding upon which gamma-tubulin ring complexes and other proteins involved in microtubule nucleation and spindle assembly become functional during mitosis.

We designed an image-based screen using automated microscopy to discover genetic factors essential for mitotic progression. Using a human genome-wide RNAi library, we performed a loss-of-function screen looking for siRNAs that arrest cells in metaphase. Supervised clustering of the multiparametric morphological data with gene ontology (GO) annotations, protein families, tissue expression and protein-protein interactions functionally classified these genes into discrete mitotic processes involved in spindle assembly. We used this approach to rapidly identify important novel genes based on their association with known genes in the clusters. We present here the automated methods used to identify these components.

Recent advances in functional genomics have enabled genome-wide genetic studies in mammalian cells. These include the establishment of high-throughput transfection and viral propagation methodologies, the production of large-scale cDNA and siRNA libraries, and the development of sensitive assay detection processes and instrumentation. The latter has been significantly facilitated by the implementation of automated microscopy and quantitative image analysis, collectively referred to as high-content screening (HCS), toward cell-based functional genomics application. This technology can be applied to whole genome analysis of discrete molecular and phenotypic events at the level of individual cells and promises to significantly expand the scope of functional genomic analyses in mammalian cells. This chapter provides a comprehensive guide for curating and preparing function genomics libraries and performing HCS at the level of the genome.

We have probed single kinetochore microtubule (k-MT) dynamics in budding yeast in the G1 phase of the cell cycle by automated tracking of a green fluorescent protein tag placed proximal to the centromere on chromosome IV and of a green fluorescent protein tag fused to the spindle pole body protein Spc42p. Our method reliably distinguishes between different dynamics in wild-type and mutant strains and under different experimental conditions. Using our methods we established that in budding yeast, unlike in metazoans, chromosomes make dynamic attachments to microtubules in G1. This makes it possible to interpret measurements of centromere tag dynamics as reflecting k-MT dynamics. We have examined the sensitivity of our assay by studying the effect of temperature, exposure to benomyl, and a tubulin mutation on k-MT dynamics. We have found that lowering the temperature and exposing cells to benomyl attenuate k-MT dynamics in a similar manner. We further observe that, in contrast to previous reports, the mutant tub2-150 forms k-MTs that depolymerize faster than wild type. Based on these findings, we propose high-resolution light microscopy of centromere dynamics in G1 yeast cells as a sensitive assay for the regulation of single k-MT dynamics.

This chapter discusses the quantitative microscopy of green fluorescent protein-labeled yeast. With the development of methods to tag proteins using green fluorescent protein (GFP), fluorescence microscopy has become increasingly important for characterizing protein function in yeast. The chapter describes the use of three-dimensional (3-D) deconvolution microscopy to perform fixed- and live-cell analysis of cells carrying GFP-tagged proteins. The chapter also discusses the process of deconvolution in fluorescence microscopy. Despite the focus on high-performance imaging, the methods described in the chapter are applicable to a wide range of experiments using conventional wide-field microscopes. The chapter describes the various steps for preparing biological samples, such as strain construction, mounting cells for microscopy, preparing slides with agar pads for live-cell microscopy, mounting cells on agar pads, mounting live cells without agar pads, fixing cells with paraformaldehyde and mounting, optimizing microscope optics, selecting filters, selecting cover glass, temperature control, minimizing spherical aberration through oil matching, acquiring images, and viewing and printing the image.

In this paper, we describe an algorithmic framework for the automatic detection of diffraction-limited fluorescent spots in 3D optical images at a separation below the Rayleigh limit, i.e. with super-resolution. We demonstrate the potential of super-resolution detection by tracking fluorescently tagged chromosomes during mitosis in budding yeast. Our biological objective is to identify and analyse the proteins responsible for the generation of tensile force during chromosome segregation. Dynamic measurements in living cells are made possible by green fluorescent protein (GFP)-tagging chromosomes and spindle pole bodies to generate cells carrying four fluorescent spots, and observe the motion of the spots over time using 3D-fluorescence microscopy. The central problem in spot detection arises with the partial or complete overlap of spots when tagged objects are separated by distances below the resolution of the optics. To detect multiple spots under these conditions, a set of candidate mixture models is built, and the best candidate is selected from the set based on chi2-statistics of the residuals in least-square fits of the models to the image data. Even with images having a signal-to-noise ratio (SNR) as low as 5-10, we are able to increase the resolution two-fold below the Rayleigh limit. In images with a SNR of 5-10, the accuracy with which isolated tags can be localized is less than 5 nm. For two tags separated by less than the Rayleigh limit, the localization accuracy is found to be between 10 and 20 nm, depending on the effective point-to-point distance. This indicates the intimate relationship between resolution and localization accuracy.

The complex series of movements that mediates chromosome segregation during mitosis is dependent on the attachment of microtubules to kinetochores, DNA-protein complexes that assemble on centromeric DNA. We describe the use of live-cell imaging and chromatin immunoprecipitation in S. cerevisiae to identify ten kinetochore subunits, among which are yeast homologs of microtubule binding proteins in animal cells. By analyzing conditional mutations in several of these proteins, we show that they are required for the imposition of tension on paired sister kinetochores and for correct chromosome movement. The proteins include both molecular motors and microtubule associated proteins (MAPs), implying that motors and MAPs function together in binding chromosomes to spindle microtubules.

Several kinesin holoenzymes, including the heterotrimeric kinesin-II and bipolar KLP61F complexes described here, are being purified in our laboratory using microtubule affinity precipitation and conventional biochemical fractionation procedures. These protocols have been optimized by using pan-kinesin peptide antibodies and subunit-specific antibodies to monitor the enrichment of kinesin-related polypeptides in particular fractions by immunoblotting. Protein purification represents the most direct route available for determining the oligomeric state and subunit composition of a kinesin holoenzyme, for identifying tightly associated accessory subunits such as SpKAP115, and for determining the molecular architecture and functional properties of native kinesin motors. Protein purification methods therefore represent an important complementary approach to molecular genetic approaches that are being pursued in many other laboratories.

Cep192 Depletion Does Not Impact Centriole Duplication but Induces Premature Centriole Disengagement Depletion of Cep192 does not appear to impact the assembly or replication of centrioles (Figure 3B and Figure S3A). The majority of Cep192 siRNA-treated cells showed four dots of centrin, corresponding to the two parental centrioles and their daughter pairs, in mitosis. However, in most of these cells, centrioles didnot localize to MTOCs. Loss of Cep192 did induce a substantial increase in the percentage of cells in which the mother and daughter centrioles became disengaged by metaphase (25% versus 5% in the control, Figure S3B). This disengagement normally occurs in telophase and is regulated by the anaphase promoting complex (APC) [S1]. We observed a similar effect after the depletion of g-tubulin, consistent with earlier reports that centriole engagement requires the presence of an intact PCM [S2, S3].