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Relationship of Lipid Rafts to Transient Confinement Zones Detected by Single Particle Tracking

Christian Dietrich et al.Jan 1, 2002

We examined the physical and chemical characteristics of transient confinement zones (TCZs) that are detected in single particle trajectories of molecules moving within the membrane of C3H 10T1/2 murine fibroblasts and their relationship to "rafts." We studied the lateral movement of different membrane molecules thought to partition to varying degrees into or out of the putative lipid domains known as rafts. We found that lipid analogs spend significantly less time in TCZs compared with Thy-1, a glycosylphosphatidylinositol-anchored protein, and GM1, a glycosphingolipid. For Thy-1, we found that zone abundance was markedly reduced by cholesterol extraction, suggesting that a major source of the observed temporary confinement is related to the presence of raft domains. More detailed analysis of particle trajectories reveals that zones can be revisited even tens of seconds after the original escape and that diffusion within the zones is reduced by a factor of ∼2, consistent with the zone being a cholesterol-rich liquid-ordered phase. Surprisingly, transient confinement was not strongly temperature dependent. Overall, our data demonstrate that there are raft-related domains present in certain regions of the plasma membrane of C3H cells, which can persist for tens of seconds.

Ecology

Biochemistry

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Majorbio Cloud: A one‐stop, comprehensive bioinformatic platform for multiomics analyses

Yi Ren et al.Mar 16, 2022

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Perturb-tracing enables high-content screening of multiscale 3D genome regulators

Yubao Cheng et al.Feb 1, 2023

Three-dimensional (3D) genome organization becomes altered during development, aging, and disease1-23, but the factors regulating chromatin topology are incompletely understood and currently no technology can efficiently screen for new regulators of multiscale chromatin organization. Here, we developed an image-based high-content screening platform (Perturb-tracing) that combines pooled CRISPR screen, a new cellular barcode readout method (BARC-FISH), and chromatin tracing. We performed a loss-of-function screen in human cells, and visualized alterations to their genome organization from 13,000 imaging target-perturbation combinations, alongside perturbation-paired barcode readout in the same single cells. Using 1.4 million 3D positions along chromosome traces, we discovered tens of new regulators of chromatin folding at different length scales, ranging from chromatin domains and compartments to chromosome territory. A subset of the regulators exhibited 3D genome effects associated with loop-extrusion and A-B compartmentalization mechanisms, while others were largely unrelated to these known 3D genome mechanisms. We found that the ATP-dependent helicase CHD7, the loss of which causes the congenital neural crest syndrome CHARGE24 and a chromatin remodeler previously shown to promote local chromatin openness25-27, counter-intuitively compacts chromatin over long range in different genomic contexts and cell backgrounds including neural crest cells, and globally represses gene expression. The DNA compaction effect of CHD7 is independent of its chromatin remodeling activity and does not require other protein partners. Finally, we identified new regulators of nuclear architectures and found a functional link between chromatin compaction and nuclear shape. Altogether, our method enables scalable, high-content identification of chromatin and nuclear topology regulators that will stimulate new insights into the 3D genome functions, such as global gene and nuclear regulation, in health and disease.

Genetics

Molecular Biology

38

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Regulated nuclear accumulation of a histone methyltransferase times the onset of heterochromatin formation inC. elegansembryos

Beste Mutlu et al.May 18, 2018

ONE SENTENCE SUMMARY MET-2/SETDB1 and interactors (LIN-65/ATF7IP and ARLE-14/ARL14EP) initiate heterochromatin formation during embryogenesis. ABSTRACT Heterochromatin formation during early embryogenesis is timed precisely, but it has been elusive how this process is regulated. Here we report the discovery of a histone methyltransferase complex whose nuclear accumulation determines the onset of heterochromatin formation in C. elegans embryos. We find that the inception of heterochromatin generation coincides with the nuclear accumulation of the methyltransferase MET-2 (SETDB). The absence of MET-2 results in delayed and disturbed heterochromatin formation, whereas accelerated nuclear localization of the methyltransferase leads to precocious heterochromatin. We identify two factors that bind to and function with MET-2: LIN-65, which resembles ATF7IP, localizes MET-2 into nuclear hubs, and ARLE-14, orthologous to ARL14EP, promotes stable association of MET-2 with chromatin. These data reveal that nuclear accumulation of MET-2 in conjunction with LIN-65 and ARLE-14 regulates timing of heterochromatin domains during embryogenesis.

Genetics

Developmental Biology

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The developmentally-timed decay of an essential microRNA family is seed sequence-dependent

Bridget Donnelly et al.Nov 20, 2021

Abstract MicroRNA (miRNA) abundance is tightly controlled by regulation of biogenesis and decay. Here we show that the mir-35 miRNA family undergoes selective decay at the transition from embryonic to larval development in C. elegans . The seed sequence of the miRNA is necessary and largely sufficient for this regulation. Sequences outside the seed (3’ end) regulate mir-35 abundance in the embryo but are not necessary for sharp decay at the transition to larval development. Enzymatic modifications of the miRNA 3’ end are neither prevalent nor correlated with changes in decay, suggesting that miRNA 3’ end display is not a core feature of this mechanism and further supporting a seed-driven decay model. Our findings demonstrate that seed sequence-specific decay can selectively and coherently regulate all redundant members of a miRNA seed family, a class of mechanism that has great biological and therapeutic potential for dynamic regulation of a miRNA family’s target repertoire.

Genetics

Molecular Biology

2

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The catalytic activity of microRNA Argonautes plays a modest role in microRNA star strand cleavage inC. elegans

Kasuen Kotagama et al.Jan 20, 2023

Abstract Many Argonaute proteins can cleave RNA (“slicing”) as part of the microRNA-induced silencing complex (miRISC), even though miRNA-mediated target repression is generally independent of target cleavage. Here we use C. elegans to examine the role of miRNA-guided slicing in organismal development. We find that unwinding and decay of the miRNA star strand is weakly defective in the absence of slicing, with the largest effect observed in embryos. Argonaute-Like Gene 2 (ALG-2) is more dependent on slicing for unwinding than ALG-1. The miRNAs that displayed the greatest (albeit very minor) dependence on slicing for unwinding tend to form stable duplexes with their star strand, and in some cases, lowering duplex stability alleviates dependence on slicing. While a few miRNA guide strands are reduced in slicing mutants, the basis of this is unclear since changes were not dependent on EBAX-1, a factor in the Target-Directed miRNA Degradation (TDMD) pathway. Gene expression and gross phenotype were wild type in slicing mutants, indicating that 1) slicing is not required for target regulation and 2) the weak unwinding defect does not significantly reduce the pool of functional miRISC. Thus, in contrast to previous work, miRISC slicing in C. elegans is dispensable in standard laboratory conditions.

Genetics

Paleontology

4

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Multiplexed imaging of nucleome architectures in single cells of mammalian tissue

Miao Liu et al.Dec 22, 2019

The three-dimensional architecture of the genome affects genomic functions. Multiple genome architectures at different length scales, including chromatin loops, domains, compartments, and regions associated with nuclear lamina and nucleoli, have been discovered. However, how these structures are arranged in the same cell and how they are correlated with each other in different cell types in mammalian tissue are largely unknown. Here, we developed Multiplexed Imaging of Nucleome Architectures that measures multiscale chromatin folding, copy numbers of numerous RNA species, and associations of numerous genomic regions with nuclear lamina, nucleoli and surface of chromosomes in the same, single cells. We applied this method in mouse fetal liver, and identified de novo cell-type-specific chromatin architectures associated with gene expression, as well as chromatin organization principles independent of cell type. Polymer simulation showed that both intra-chromosomal phase-separating interactions and extra-chromosomal interactions are necessary to establish the observed organization. Our experiments and modeling provide a multiscale and multi-faceted picture of chromatin folding and nucleome architectures in mammalian tissue and illustrate physical principles for maintaining chromatin organization.

Genetics

Molecular Biology

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The Hippo pathway origin and its oncogenic alteration in evolution

Yuxuan Chen et al.Nov 11, 2019

The Hippo pathway is a central regulator of organ size and a key tumor suppressor via coordinating cell proliferation and death. Initially discovered in Drosophila, the Hippo pathway has been implicated as an evolutionarily conserved pathway in mammals; however, how this pathway was evolved to be functional from its origin is still largely unknown. In this study, we traced the Hippo pathway in premetazoan species, characterized the intrinsic functions of its ancestor components, and unveiled the evolutionary history of this key signaling pathway from its unicellular origin. In addition, we elucidated the paralogous gene history for the mammalian Hippo pathway components and characterized their cancer-derived somatic mutations from an evolutionary perspective. Taken together, our findings not only traced the conserved function of the Hippo pathway to its unicellular ancestor components, but also provided novel evolutionary insights into the Hippo pathway organization and oncogenic alteration.

Genetics

History

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Genetics

History

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