Rosanne Boudreau

Biological applications of colloidal nanocrystals

Due to their interesting properties, research on colloidal nanocrystals has moved in the last few years from fundamental research to first applications in materials science and life sciences. In this review some recent biological applications of colloidal nanocrystals are discussed, without going into biological or chemical details. First, the properties of colloidal nanocrystals and how they can be synthesized are described. Second, the conjugation of nanocrystals with biological molecules is discussed. And third, three different biological applications are introduced: (i) the arrangement of nanocrystal–oligonucleotide conjugates using molecular scaffolds such as single-stranded DNA, (ii) the use of nanocrystal–protein conjugates as fluorescent probes for cellular imaging, and (iii) a motility assay based on the uptake of nanocrystals by living cells.

Cell motility and metastatic potential studies based on quantum dot imaging of phagokinetic tracks

A wide variety of eukaryotic cells are shown to engulf colloidal semiconductor nanocrystals, or quantum dots, when they migrate. Here we show that the uptake of the nanocrystals is directly correlated with the cell motility, by comparing in detail the motions of both cancerous and healthy human breast cancer cells, as well as several other cell types. The nanocrystals are more photochemically robust than organic dyes (which fade quickly) and do not perturb the cells. The ability to examine these behaviors in live cells over extended time periods, and to quantify changes in response to various molecular manipulations, provides a powerful tool for studying the processes of cell motility and migration – behaviors that are responsible for metastases of primary cancers.

Nanoimaging Cells Using Soft X-Ray Tomography

Soft X-ray microscopy is ideally suited to visualizing and quantifying biological cells. Specimens, including eukaryotic cells, are imaged intact, unstained and fully hydrated, and therefore visualized in a near-native state. The contrast in soft X-ray microscopy is generated by the differential attenuation of X-rays by the molecules in the specimen-water is relatively transmissive to this type of illumination compared to carbon and nitrogen. The attenuation of X-rays by the specimen follows the Beer-Lambert law, and therefore both linear and a quantitative measure of thickness and chemical species present at each point in the cell. In this chapter, we will describe the procedures and computational methods that lead to 50 nm (or better) tomographic reconstructions of cells using soft X-ray microscope data, and the subsequent segmentation and analysis of these volumetric reconstructions. In addition to being a high-fidelity imaging modality, soft X-ray tomography is relatively high-throughput; a complete tomographic data set can be collected in a matter of minutes. This new modality is being applied to imaging cells that range from small prokaryotes to stem cells obtained from mammalian tissues.

Measuring Cell Motility Using Quantum Dot Probes

The ability of cancer cells to migrate and metastasize is known to be directly related to tumor cell motility. Therefore, assaying the level of tumor cell motility is an excellent indicator of metastatic potential. We have developed an efficient and sensitive two-dimensional cell motility assay to image the phagokinetic uptake of colloidal CdSe/ZnS semiconductor nanocrystals (quantum dots [QDs]). As cells move across a thin, homogeneous layer of QDs, they engulf and uptake the nanocrystals and leave behind a fluorescent-free trail. By measuring the ratio of trail area to cell area we have discovered that it is possible to distinguish between noninvasive and invasive cancer cells lines. This technique has, therefore, the potential to be used as a rapid, robust, and quantitative in vitro measure of metastatic potential. Because the technique only relies on fluorescence detection, requires no significant data processing, and is used with live cells, it is both rapid and straightforward.

Quantum Dot-Based Cell Motility Assay

Because of their favorable physical and photochemical properties, colloidal CdSe/ZnS-semiconductor nanocrystals (commonly known as quantum dots) have enormous potential for use in biological imaging. In this report, we present an assay that uses quantum dots as markers to quantify cell motility. Cells that are seeded onto a homogeneous layer of quantum dots engulf and absorb the nanocrystals and, as a consequence, leave behind a fluorescence-free trail. By subsequently determining the ratio of cell area to fluorescence-free track area, we show that it is possible to differentiate between invasive and noninvasive cancer cells. Because this assay uses simple fluorescence detection, requires no significant data processing, and can be used in live-cell studies, it has the potential to be a powerful new tool for discriminating between invasive and noninvasive cancer cell lines or for studying cell signaling events involved in migration.

Visualizing red blood cell sickling and the effects of inhibition of sphingosine kinase 1 using soft X-ray tomography.

ABSTRACT Sickle cell disease is a destructive genetic disorder characterized by the formation of fibrils of deoxygenated hemoglobin, leading to the red blood cell (RBC) morphology changes that underlie the clinical manifestations of this disease. Using cryogenic soft X-ray tomography (SXT), we characterized the morphology of sickled RBCs in terms of volume and the number of protrusions per cell. We were able to identify statistically a relationship between the number of protrusions and the volume of the cell, which is known to correlate to the severity of sickling. This structural polymorphism allows for the classification of the stages of the sickling process. Recent studies have shown that elevated sphingosine kinase 1 (Sphk1)-mediated sphingosine 1-phosphate production contributes to sickling. Here, we further demonstrate that compound 5C, an inhibitor of Sphk1, has anti-sickling properties. Additionally, the variation in cellular morphology upon treatment suggests that this drug acts to delay the sickling process. SXT is an effective tool that can be used to identify the morphology of the sickling process and assess the effectiveness of potential therapeutics. Highlighted Article: Soft X-ray cryotomography revealed an inverse relationship between sickle RBC volume and number of protrusions upon sickling. Subtomogram analysis showed beneficial effects with Sphk1 inhibitor treatment.

Integrated systems biology and imaging of the smallest free-living eukaryote Ostreococcus tauri

Ostreococcus tauri is an ancient phototrophic microalgae that possesses favorable genetic and cellular characteristics for reductionist studies probing biosystem design and dynamics. Here multimodal bioimaging and multi-omics techniques were combined to interrogate O. tauri cellular changes in response to variations in bioavailable nitrogen and carbon ratios. Confocal microscopy, stimulated Raman scattering, and cryo-soft x-ray tomography revealed whole cell ultrastructural dynamics and composition while proteomic and lipidomic profiling captured changes at the molecular and macromolecular scale. Despite several energy dense long-chain triacylglycerol lipids showing more than 40-fold higher abundance under N deprivation, only a few proteins directly associated with lipid biogenesis showed significant expression changes. However, the entire pathway for starch granule biosynthesis was highly upregulated suggesting much of the cellular energy is preferentially directed towards starch over lipid accumulation. Additionally, three of the five most downregulated and five of the ten most upregulated proteins during severe nitrogen depletion were unnamed protein products that warrant additional biochemical analysis and functional annotation to control carbon transformation dynamics in this smallest eukaryote.

Ostreococcus tauri is a high-lipid content green algae that extrudes clustered lipid droplets

Lipid droplet biogenesis, accumulation and secretion is an important field of research spanning biofuel feedstock production in algae and yeast to plant-microbe symbiosis or human metabolic disorders and other diseases. Here we evaluate the critical elements that influence lipid accumulation in the highly simplified and smallest known eukaryote Ostreococcus tauri and identify several conditions that satisfy its classification as an oleaginous green alga. In addition, these experiments revealed the release of excess lipids in pea-pod like structures where many dense lipid droplets are clustered in a linear fashion surrounded by an enveloping membrane which contrasts with known mechanisms from other eukaryotes. These results highlight the potential for Ostreococcus tauri to probe the evolution of lipid droplet dynamics as an emerging model organism with a compacted eukaryotic genome and also to impact lipid feedstock bioproduction applications either directly or using synthetic biology. One Sentence Summary The smallest known eukaryote Ostreococcus tauri is oleaginous and sheds lipid droplets as pea-pod like membrane enclosed clusters.

Quantitative Analyzing the Spatial Organization of the Organelles in Cancer Cell Using Soft X-Ray Tomography

Using soft x-ray microscopy (SXM), we are able to image and quantitatively analyze the spatial organization of the organelles within cancer cells [1]. Crucial cellular activities, such as cancer invasion and metastasis, mostly take place within a three-dimensional extracellular matrix (ECM) [2]. Thus, the information of three-dimensional organization of organelles in cancer cells is required to tackle questions regarding those highly remodeling activities.

The National Center for X-Ray Tomography: Status Update

The National Center for X-ray Tomography (NCXT) develops new technologies for bio-imaging. In particular, the NCXT pioneered the development of soft x-ray tomography (SXT) as a method for imaging whole, hydrated cells, including eukaryotic cells. This presentation will describe the current status of this work, together our progress incorporating ‘super-resolution’ cryogenic SIM as a correlative partner for SXT.