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Liu Lab / Publications
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43 Publications

Showing 1-10 of 43 results
07/01/21 | Biomolecular Condensates and Their Links to Cancer Progression.
Cai D, Liu Z, Lippincott-Schwartz J
Trends in Biochemical Sciences. 2021 Jul 01;46(7):535-549. doi: 10.1016/j.tibs.2021.01.002

Liquid-liquid phase separation (LLPS) has emerged in recent years as an important physicochemical process for organizing diverse processes within cells via the formation of membraneless organelles termed biomolecular condensates. Emerging evidence now suggests that the formation and regulation of biomolecular condensates are also intricately linked to cancer formation and progression. We review the most recent literature linking the existence and/or dissolution of biomolecular condensates to different hallmarks of cancer formation and progression. We then discuss the opportunities that this condensate perspective provides for cancer research and the development of novel therapeutic approaches, including the perturbation of condensates by small-molecule inhibitors.

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07/01/21 | Single-cell imaging of genome organization and dynamics.
Xie L, Liu Z
Molecular Systems Biology. 2021 Jul 01;17(7):e9653. doi: 10.15252/msb.20209653

Probing the architecture, mechanism, and dynamics of genome folding is fundamental to our understanding of genome function in homeostasis and disease. Most chromosome conformation capture studies dissect the genome architecture with population- and time-averaged snapshots and thus have limited capabilities to reveal 3D nuclear organization and dynamics at the single-cell level. Here, we discuss emerging imaging techniques ranging from light microscopy to electron microscopy that enable investigation of genome folding and dynamics at high spatial and temporal resolution. Results from these studies complement genomic data, unveiling principles underlying the spatial arrangement of the genome and its potential functional links to diverse biological activities in the nucleus.

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05/24/21 | A general method to improve fluorophores using deuterated auxochromes.
Grimm JB, Xie L, Casler JC, Patel R, Tkachuk AN, Falco N, Choi H, Lippincott-Schwartz J, Brown TA, Glick BS, Liu Z, Lavis LD
JACS Au. 2021 May 24;1(5):690-6. doi: 10.1021/jacsau.1c00006

Fluorescence microscopy relies on dyes that absorb and then emit photons. In addition to fluorescence, fluorophores can undergo photochemical processes that decrease quantum yield or result in spectral shifts and irreversible photobleaching. Chemical strategies that suppress these undesirable pathways—thereby increasing the brightness and photostability of fluorophores—are crucial for advancing the frontier of bioimaging. Here, we describe a general method to improve small-molecule fluorophores by incorporating deuterium into the alkylamino auxochromes of rhodamines and other dyes. This strategy increases fluorescence quantum yield, inhibits photochemically induced spectral shifts, and slows irreparable photobleaching, yielding next-generation labels with improved performance in cellular imaging experiments.

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02/10/21 | Biomolecular Condensates and Their Links to Cancer Progression.
Cai D, Liu Z, Lippincott-Schwartz J
Trends in Biochemical Sciences. 2021 Feb 10:. doi: 10.1016/j.tibs.2021.01.002

Liquid-liquid phase separation (LLPS) has emerged in recent years as an important physicochemical process for organizing diverse processes within cells via the formation of membraneless organelles termed biomolecular condensates. Emerging evidence now suggests that the formation and regulation of biomolecular condensates are also intricately linked to cancer formation and progression. We review the most recent literature linking the existence and/or dissolution of biomolecular condensates to different hallmarks of cancer formation and progression. We then discuss the opportunities that this condensate perspective provides for cancer research and the development of novel therapeutic approaches, including the perturbation of condensates by small-molecule inhibitors.

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12/13/20 | Two-parameter single-molecule analysis for measurement of chromatin mobility.
Lerner J, Gomez-Garcia PA, McCarthy RL, Liu Z, Lakadamyali M, Zaret KS
STAR Protocols. 2020 Dec 13;1(3):100223. doi: 10.1016/j.xpro.2020.100223

This protocol provides a two-parameter analysis of single-molecule tracking (SMT) trajectories of Halo-tagged histones in living adherent cell lines and unveils a chromatin mobility landscape composed of five chromatin types, ranging from low to high mobility. When the analysis is applied to Halo-tagged, chromatin-binding proteins, it associates chromatin interaction properties with known functions in a way that previously used SMT parameters did not. For complete information on the use and execution of this protocol, please refer to Lerner et al. (2020).

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08/20/20 | Rational design of bioavailable photosensitizers for manipulation and imaging of biological systems.
Binns TC, Ayala AX, Grimm JB, Tkachuk AN, Castillon GA, Phan S, Zhang L, Brown TA, Liu Z, Adams SR, Ellisman MH, Koyama M, Lavis LD
Cell Chemical Biology. 2020 Aug 20;27(8):1063-72. doi: 10.1016/j.chembiol.2020.07.001

Light-mediated chemical reactions are powerful methods for manipulating and interrogating biological systems. Photosensitizers, compounds that generate reactive oxygen species upon excitation with light, can be utilized for numerous biological experiments, but the repertoire of bioavailable photosensitizers is limited. Here, we describe the synthesis, characterization, and utility of two photosensitizers based upon the widely used rhodamine scaffold and demonstrate their efficacy for chromophore-assisted light inactivation, cell ablation in culture and in vivo, and photopolymerization of diaminobenzidine for electron microscopy. These chemical tools will facilitate a broad range of applications spanning from targeted destruction of proteins to high-resolution imaging.

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08/01/20 | Two-parameter mobility assessments discriminate diverse regulatory factor behaviors in chromatin.
Lerner J, Gomez-Garcia PA, McCarthy RL, Liu Z, Lakadamyali M, Zaret KS
Molecular Cell. 2020 Aug 1;79(4):677. doi: 10.1016/j.molcel.2020.05.036

Enzymatic probes of chromatin structure reveal accessible versus inaccessible chromatin states, while super-resolution microscopy reveals a continuum of chromatin compaction states. Characterizing histone H2B movements by single-molecule tracking (SMT), we resolved chromatin domains ranging from low to high mobility and displaying different subnuclear localizations patterns. Heterochromatin constituents correlated with the lowest mobility chromatin, whereas transcription factors varied widely with regard to their respective mobility with low- or high-mobility chromatin. Pioneer transcription factors, which bind nucleosomes, can access the low-mobility chromatin domains, whereas weak or non-nucleosome binding factors are excluded from the domains and enriched in higher mobility domains. Nonspecific DNA and nucleosome binding accounted for most of the low mobility of strong nucleosome interactor FOXA1. Our analysis shows how the parameters of the mobility of chromatin-bound factors, but not their diffusion behaviors or SMT-residence times within chromatin, distinguish functional characteristics of different chromatin-interacting proteins.

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07/27/20 | A general method to optimize and functionalize red-shifted rhodamine dyes.
Grimm JB, Tkachuk AN, Xie L, Choi H, Mohar B, Falco N, Schaefer K, Patel R, Zheng Q, Liu Z, Lippincott-Schwartz J, Brown TA, Lavis LD
Nature Methods. 2020 Jul 27:. doi: 10.1038/s41592-020-0909-6

Expanding the palette of fluorescent dyes is vital to push the frontier of biological imaging. Although rhodamine dyes remain the premier type of small-molecule fluorophore owing to their bioavailability and brightness, variants excited with far-red or near-infrared light suffer from poor performance due to their propensity to adopt a lipophilic, nonfluorescent form. We report a framework for rationalizing rhodamine behavior in biological environments and a general chemical modification for rhodamines that optimizes long-wavelength variants and enables facile functionalization with different chemical groups. This strategy yields red-shifted 'Janelia Fluor' (JF) dyes useful for biological imaging experiments in cells and in vivo.

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07/20/20 | Microdomains form on the luminal face of neuronal extracellular vesicle membranes.
Matthies D, Lee NY, Gatera I, Pasolli HA, Zhao X, Liu H, Walpita D, Liu Z, Yu Z, Ioannou MS
Scientific Reports. 2020 Jul 20;10(1):11953. doi: 10.1038/s41598-020-68436-x

Extracellular vesicles (EVs) are important mediators of cell-to-cell communication and have been implicated in several pathologies including those of the central nervous system. They are released by all cell types, including neurons, and are highly heterogenous in size and composition. Yet much remains unknown regarding the biophysical characteristics of different EVs. Here, using cryo-electron microscopy (cryoEM), we analyzed the size distribution and morphology of EVs released from primary cortical neurons. We discovered massive macromolecular clusters on the luminal face of EV membranes. These clusters are predominantly found on medium-sized vesicles, suggesting that they may be specific to microvesicles as opposed to exosomes. We propose that these clusters serve as microdomains for EV signaling and play an important role in EV physiology.

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06/17/20 | Genome-wide kinetic properties of transcriptional bursting in mouse embryonic stem cells.
Ochiai H, Hayashi T, Umeda M, Yoshimura M, Harada A, Shimizu Y, Nakano K, Saitoh N, Liu Z, Yamamoto T, Okamura T, Ohkawa Y, Kimura H, Nikaido I
Science Advances. 2020 Jun 17;6(25):eaaz6699. doi: 10.1126/sciadv.aaz6699

Transcriptional bursting is the stochastic activation and inactivation of promoters, contributing to cell-to-cell heterogeneity in gene expression. However, the mechanism underlying the regulation of transcriptional bursting kinetics (burst size and frequency) in mammalian cells remains elusive. In this study, we performed single-cell RNA sequencing to analyze the intrinsic noise and mRNA levels for elucidating the transcriptional bursting kinetics in mouse embryonic stem cells. Informatics analyses and functional assays revealed that transcriptional bursting kinetics was regulated by a combination of promoter- and gene body-binding proteins, including the polycomb repressive complex 2 and transcription elongation factors. Furthermore, large-scale CRISPR-Cas9-based screening identified that the Akt/MAPK signaling pathway regulated bursting kinetics by modulating transcription elongation efficiency. These results uncovered the key molecular mechanisms underlying transcriptional bursting and cell-to-cell gene expression noise in mammalian cells.

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