A simple filtration technique for obtaining purified human chromosomes in suspension

Quantitative catalogue of mammalian mitotic chromosome-associated RNAs

The faithful transmission of a cell's identity and functionality to its daughters during mitosis requires the proper assembly of mitotic chromosomes from interphase chromatin in a process that involves significant changes in the genome-bound material, including the RNA. However, our understanding of the RNA that is associated with the mitotic chromosome is presently limited. Here, we present complete and quantitative characterizations of the full-length mitotic chromosome-associated RNAs (mCARs) for 3 human cell lines, a monkey cell line, and a mouse cell line derived from high-depth RNA sequencing (3 replicates, 47 M mapped read pairs for each replicate). Overall, we identify, on average, more than 20,400 mCAR species per cell-type (including isoforms), more than 5,200 of which are enriched on the chromosome. Notably, overall, more than 2,700 of these mCARs were previously unknown, which thus also expands the annotated genome of these species. We anticipate that these datasets will provide an essential resource for future studies to better understand the functioning of mCARs on the mitotic chromosome and in the cell.

Genome-wide identification of mammalian cell-cycle invariant and mitotic-specific macroH2A1 domains

The histone variant macroH2A has been found to play important regulatory roles in genomic processes, especially in regulating transcriptomes. However, whether macroH2A nucleosomes are retained on mitotic chromosomes to enable maintenance of cell-specific transcriptomes is not known. Here, examining mouse embryonic fibroblast cells (NIH-3T3) with native chromatin immunoprecipitation and sequencing (nChIP-seq), we show that the overwhelming majority (~90%) of macroH2A1 domains identified at the G1/S stage are indeed stably retained on mitotic chromosomes. Unexpectedly though, we also find that there are a number of macroH2A domains that are specific for either mitotic or G1/S cells. Notably, more than 7,000 interphase expressed genes flanked by macroH2A1 domains are loaded with macroH2A1 nucleosomes on the mitotic chromosome to form extended domains. Overall, these results reveal that, while the majority of macroH2A1 domains are indeed faithfully transmitted through the mitotic chromosomes, there is a previously unknown cell-cycle dependent exchange of macroH2A1 nucleosomes at numerous genomic loci, indicating the existence of molecular machineries for this dynamically regulated process. We anticipate that these findings will prove to be essential for the integrity of mitotic progression and the maintenance of cellular identity.

Quantitative phase measurements of human cell nuclei using X-ray ptychography

The human cell nucleus serves as an important organelle holding the genetic blueprint for life. In this work, X-ray ptychography was applied to assess the masses of human cell nuclei using its unique phase shift information. Measurements were carried out at the I13-1 beamline at the Diamond Light Source that has extremely large transverse coherence properties. The ptychographic diffractive imaging approach allowed imaging of large structures that gave quantitative measurements of the phase shift in 2D projections. In this paper a modified ptychography algorithm that improves the quality of the reconstruction for weak scattering samples is presented. The application of this approach to calculate the mass of several human nuclei is also demonstrated.

Ultra-Structural Imaging Provides 3D Organization of 46 Chromosomes of a Human Lymphocyte Prophase Nucleus

Three dimensional (3D) ultra-structural imaging is an important tool for unraveling the organizational structure of individual chromosomes at various stages of the cell cycle. Performing hitherto uninvestigated ultra-structural analysis of the human genome at prophase, we used serial block-face scanning electron microscopy (SBFSEM) to understand chromosomal architectural organization within 3D nuclear space. Acquired images allowed us to segment, reconstruct, and extract quantitative 3D structural information about the prophase nucleus and the preserved, intact individual chromosomes within it. Our data demonstrate that each chromosome can be identified with its homolog and classified into respective cytogenetic groups. Thereby, we present the first 3D karyotype built from the compact axial structure seen on the core of all prophase chromosomes. The chromosomes display parallel-aligned sister chromatids with familiar chromosome morphologies with no crossovers. Furthermore, the spatial positions of all 46 chromosomes revealed a pattern showing a gene density-based correlation and a neighborhood map of individual chromosomes based on their relative spatial positioning. A comprehensive picture of 3D chromosomal organization at the nanometer level in a single human lymphocyte cell is presented.

X-ray Ptychography Imaging of Human Chromosomes After Low-dose Irradiation

Studies of the structural and functional role of chromosomes in cytogenetics have spanned more than 10 decades. In this work, we take advantage of the coherent X-rays available at the latest synchrotron sources to extract the individual masses of all 46 chromosomes of metaphase human B and T cells using hard X-ray ptychography. We have produced ‘X-ray karyotypes’ of both heavy metal–stained and unstained spreads to determine the gain or loss of genetic material upon low-level X-ray irradiation doses due to radiation damage. The experiments were performed at the I-13 beamline, Diamond Light Source, Didcot, UK, using the phase-sensitive X-ray ptychography method.

Size and shape based chromosome separation in the inertial focusing device

In this paper, we use a spiral channel inertial focusing device for isolation and purification of chromosomes, which are highly asymmetric. The method developed is proposed as a sample preparation process for transchromosomic research. The proposed microfluidics-based chromosome separation approach enables rapid, label-free isolation of bioactive chromosomes and is compatible with chromosome buffer. As part of this work, particle force analysis during the separation process is performed utilizing mathematic models to estimate the expected behavior of chromosomes in the channel and the model validated with experiments employing fluorescent beads. The chromosome sample is further divided into subtypes utilizing fluorescent activated cell sorting , including small condensed chromosomes, single chromosomes, and groups of two chromosomes (four sister chromatids). The separation of chromosome subtypes is realized based on their shape differences in the spiral channel device under high flow rate conditions. When chromosomes become aligned in the shear flow, the balance between the inertial focusing force and the Dean flow drag force is determined by the chromosome projection area and aspect ratio, or shape difference, leading to different focusing locations in the channel. The achieved results indicate a new separation regime in inertial microfluidics that can be used for the separation of non-spherical particles based on particle aspect ratios, which could potentially be applied in fields such as bacteria subtype separation and chromosome karyotyping.

Pressurized DNA state inside herpes capsids-A novel antiviral target

Drug resistance in viruses represents one of the major challenges of healthcare. As part of an effort to provide a treatment that avoids the possibility of drug resistance, we discovered a novel mechanism of action (MOA) and specific compounds to treat all nine human herpesviruses and animal herpesviruses. The novel MOA targets the pressurized genome state in a viral capsid, "turns off" capsid pressure, and blocks viral genome ejection into a cell nucleus, preventing viral replication. This work serves as a proof-of-concept to demonstrate the feasibility of a new antiviral target-suppressing pressure-driven viral genome ejection-that is likely impervious to developing drug resistance. This pivotal finding presents a platform for discovery of a new class of broad-spectrum treatments for herpesviruses and other viral infections with genome-pressure-dependent replication. A biophysical approach to antiviral treatment such as this is also a vital strategy to prevent the spread of emerging viruses where vaccine development is challenged by high mutation rates or other evasion mechanisms.

Use of 3D imaging for providing insights into high-order structure of mitotic chromosomes

The high-order structure of metaphase chromosomes remains still under investigation, especially the 30-nm structure that is still controversial. Advanced 3D imaging has provided useful information for our understanding of this detailed structure. It is evident that new technologies together with improved sample preparations and image analyses should be adequately combined. This mini review highlights 3D imaging used for chromosome analysis so far with future imaging directions also highlighted.

Nuclear incorporation of iron during the eukaryotic cell cycle

Scanning X-ray fluorescence microscopy has been used to probe the distribution of S, P and Fe within cell nuclei. Nuclei, which may have originated at different phases of the cell cycle, are found to show very different levels of Fe present with a strongly inhomogeneous distribution. P and S signals, presumably from DNA and associated nucleosomes, are high and relatively uniform across all the nuclei; these agree with X-ray phase contrast projection microscopy images of the same samples. Possible reasons for the Fe incorporation are discussed.

Challenges, Solutions, and Quality Metrics of Personal Genome Assembly in Advancing Precision Medicine

Even though each of us shares more than 99% of the DNA sequences in our genome, there are millions of sequence codes or structure in small regions that differ between individuals, giving us different characteristics of appearance or responsiveness to medical treatments. Currently, genetic variants in diseased tissues, such as tumors, are uncovered by exploring the differences between the reference genome and the sequences detected in the diseased tissue. However, the public reference genome was derived with the DNA from multiple individuals. As a result of this, the reference genome is incomplete and may misrepresent the sequence variants of the general population. The more reliable solution is to compare sequences of diseased tissue with its own genome sequence derived from tissue in a normal state. As the price to sequence the human genome has dropped dramatically to around $1000, it shows a promising future of documenting the personal genome for every individual. However, de novo assembly of individual genomes at an affordable cost is still challenging. Thus, till now, only a few human genomes have been fully assembled. In this review, we introduce the history of human genome sequencing and the evolution of sequencing platforms, from Sanger sequencing to emerging "third generation sequencing" technologies. We present the currently available de novo assembly and post-assembly software packages for human genome assembly and their requirements for computational infrastructures. We recommend that a combined hybrid assembly with long and short reads would be a promising way to generate good quality human genome assemblies and specify parameters for the quality assessment of assembly outcomes. We provide a perspective view of the benefit of using personal genomes as references and suggestions for obtaining a quality personal genome. Finally, we discuss the usage of the personal genome in aiding vaccine design and development, monitoring host immune-response, tailoring drug therapy and detecting tumors. We believe the precision medicine would largely benefit from bioinformatics solutions, particularly for personal genome assembly.

Staining and embedding of human chromosomes for 3-d serial block-face scanning electron microscopy

The high-order structure of human chromosomes is an important biological question that is still under investigation. Studies have been done on imaging human mitotic chromosomes using mostly 2-D microscopy methods. To image micron-sized human chromosomes in 3-D, we developed a procedure for preparing samples for serial block-face scanning electron microscopy (SBFSEM). Polyamine chromosomes are first separated using a simple filtration method and then stained with heavy metal. We show that the DNA-specific platinum blue provides higher contrast than osmium tetroxide. A two-step procedure for embedding chromosomes in resin is then used to concentrate the chromosome samples. After stacking the SBFSEM images, a familiar X-shaped chromosome was observed in 3-D.