Biology subjects

Kirschner, M. W.

Publications and source records attributed to Kirschner, M. W..

31 records · Page 2Linked to original sources

bioRxiv2020

An optimal set of inhibitors for Reverse Engineering via Kinase Regularization.

We present a comprehensive resource of 257 kinase inhibitor profiles against 365 human protein kinases using gold-standard kinase activity assays. We show the utility of this dataset with an improved version of Kinome Regularization (KiR) to deconvolve protein kinases involved in a cellular phenotype. We assayed protein kinase inhibitors against more than 70% of the human protein kinome and chose an optimal subset of 58 inhibitors to assay at ten doses across four orders of magnitude. We demonstrate the effectiveness of KiR to identify key kinases by using a quantitative cell migration assay and updated machine learning methods. This approach can be widely applied to biological problems for which a quantitative phenotype can be measured and which can be perturbed with our set of kinase inhibitors.

systems biology↗

bioRxiv2020

Non-canonical open reading frames encode functional proteins essential for cancer cell survival

A key question in genome research is whether biologically active proteins are restricted to the [~]20,000 canonical, well-annotated genes, or rather extend to the many non-canonical open reading frames (ORFs) predicted by genomic analyses. To address this, we experimentally interrogated 553 ORFs nominated in ribosome profiling datasets. Of these 553 ORFs, 57 (10%) induced a viability defect when the endogenous ORF was knocked out using CRISPR/Cas9 in 8 human cancer cell lines, 257 (46%) showed evidence of protein translation when ectopically expressed in HEK293T cells, and 401 (73%) induced gene expression changes measured by transcriptional profiling following ectopic expression across 4 cell types. CRISPR tiling and start codon mutagenesis indicated that the biological effects of these non-canonical ORFs required their translation as opposed to RNA-mediated effects. We selected one of these ORFs, G029442--renamed GREP1 (Glycine-Rich Extracellular Protein-1)--for further characterization. We found that GREP1 encodes a secreted protein highly expressed in breast cancer, and its knock-out in 263 cancer cell lines showed preferential essentiality in breast cancer derived lines. Analysis of the secretome of GREP1-expressing cells showed increased abundance of the oncogenic cytokine GDF15, and GDF15 supplementation mitigated the growth inhibitory effect of GREP1 knock-out. Taken together, these experiments suggest that the non-canonical ORFeome is surprisingly rich in biologically active proteins and potential cancer therapeutic targets deserving of further study.

cancer biology↗

bioRxiv2019

Quantitative proteomics reveals remodeling of protein repertoire across life phases of Daphnia pulex

The microcrustacean Daphnia is becoming an organism of choice for genomic and proteomic studies of the effects of environmental stressors. However, the changes in protein expression across the life cycle have not been fully characterized. We analyzed the proteomes of adult females, juveniles, asexually produced embryos, and the ephippia - resting stages containing two sexually produced diapausing freezing- and desiccation-resistant embryos. Overall, we were significantly more likely to detect proteins with known molecular functions than proteins with no detectable orthology. Similarly we could detect those with stronger gene model support, as judged by mutual best BLAST hits between two independent genome assemblies than those without such support. This suggests that we could apply our proteomics pipeline to verify hypothesized proteins, even given less-than-perfect reference gene models. In particular, we observed up-regulation of vitellogenins and down-regulation of actins and myosins in embryos of both types, as compared to juveniles and adults and overrepresentation of cell-cycle related proteins in the developing embryos, as compared to both diapausing embryos and adults. We found upregulation of small heat-shock proteins and redox peroxidases, as well as overrepresentation of stress-response proteins in the ephippium relative to the asexually produced non-diapausing embryos. The ephippium also showed up-regulation of three trehalose-synthesis proteins and down-regulation of a trehalose hydrolase, consistent with the role of trehalose in protection against freezing and desiccation.\n\nStatement of significance of the studyFreshwater plankton crustacean Daphnia is rapidly becoming a model organism of choice for ecological and developmental genomics. While there have been several advances towards establishing the protocols and reference datasets for proteomics, a detailed dataset covering several main steps of asexual and sexual phases of Daphnia life cycle is not yet available. Moreover, different versions of D. pulex genome differ in the number of protein-coding genes identified; it is unclear whether these differences are caused by differences between sequenced genotypes or between gene model methodology used. In this study we report LC-MS2/MS3 proteomes of whole body adult females, juvenile females, asexually produces embryos and diapausing eggs capable of surviving freezing and desiccation.

systems biology↗

bioRxiv2019

Single molecule dynamics of Dishevelled at the plasma membrane and Wnt pathway activation

Dvl (Dishevelled) is one of several essential non-enzymatic components of the Wnt signaling pathway. In most current models, Dvl forms complexes with Wnt ligand receptors, Fzd and LRP5/6 at the plasma membrane, which then recruits other components of the destruction complex leading to inactivation of {beta}-catenin degradation. Although this model is widespread, direct evidence for this process is lacking. In this study, we tagged mEGFP to C-terminus of dishevlled2 gene using CRISPR/Cas9 induced homologous recombination and observed its dynamics directly at the single molecule level with Total Internal Reflection Fluorescence (TIRF) microscopy. We focused on two questions: 1) What is the native size and the dynamic features of membrane-associated Dvl complexes during Wnt pathway activation? 2) What controls the behavior of these complexes? We found that membrane bound Dvl2 is predominantly monomer in the absent of Wnt (mean size 1.10). Wnt3a stimulation leads to an increase in the total concentration of membrane-bound Dvl2 from 0.08/m2 to 0.34/m2. Wnt3a also leads to increased oligomerization which raises the weighted averaged mean size of Dvl2 complexes to 1.4; with 65% of Dvl still as monomers. The driving force for Dvl2 oligomerization is the increased concentration of Dvl2 at the membrane caused by increased affinity of Dvl2 for Fzd, the Dvl2 and Fzd binding is independent of LRP5/6. The oligomerized Dvl2 complexes have greatly increased dwell time, 2~3 minutes compared to less than 1 second for monomeric Dvl2. These properties make Dvl a unique scaffold dynamically changing its state of assembly and stability at the membrane in response to Wnt ligands.\n\nSignificance StatementCanonical Wnt signaling is one of the most widely distributed pathways in metazoan development. Despite intense genetic and biochemical study for over 35 years, the major features of signaling across the plasma membrane are still poorly understood. Dishevelled serves as an essential bridge between the membrane receptors and downstream signaling components. Attempts to reconstruct the pathway and analyze its biochemical features in vitro have been hampered by Dishevelleds tendency to aggregate in vitro and to form large aggregates of dubious significance in vivo. To obtain a molecular understanding of the role of Dvl in Wnt signaling, while circumventing these aggregation problems we have expressed a fluorescent tagged Dishevelled in cells at their physiological concentration and quantified the size distribution of Dishevelled before and after Wnt treatment. We found that limited oligomerization in response to the Wnt ligand is very dynamic and provides a key step of signal transduction.

systems biology↗

bioRxiv2019

In situ measurement of absolute concentrations by Normalized Raman Imaging

Cell mass and its chemical composition are important aggregate cellular variables for physiological processes including growth control and tissue homeostasis. Despite their central importance, it has been difficult to quantitatively measure these quantities from single cells in intact tissue. Here, we introduce Normalized Raman Imaging (NoRI), a Stimulated Raman Scattering (SRS) microscopy method that provides the local concentrations of protein, lipid and water from live or fixed tissue samples with high spatial resolution. Using NoRI, we demonstrate that single cell protein, lipid and water concentrations are maintained in a tight range in cells under same physiological conditions and are altered in different physiological states such as cell cycle stages, attachment to substrates of different stiffness, or by entering senescence. In animal tissues, protein and lipid concentration varies with cell types, yet an unexpected cell-to-cell heterogeneity was found in cerebellar Purkinje cells. Protein and lipid concentration profile provides a new means to quantitatively compare disease-related pathology as demonstrated using models of Alzheimers disease. Our demonstration shows that NoRI is a broadly applicable tool for probing the biological regulation of protein mass, lipid mass and water in cellular and tissue growth, homeostasis, and disease.

bioengineering↗

bioRxiv2019

Optimization of Quantitative Phase Microscopy reveals new features of the growth rate of adherent mammalian cells

The fine balance of growth and division is a fundamental property of the physiology of cells and one of the least understood. Its study has been thwarted by difficulties in the accurate measurement of cell size and the even greater challenges of measuring growth of a single-cell over time. We address these limitations by demonstrating a new computationally enhanced methodology for Quantitative Phase Microscopy (ceQPM) for adherent cells, using improved image processing algorithms and automated cell tracking software. Accuracy has been improved more than two-fold and this improvement is sufficient to establish the dynamics of cell growth and adherence to simple growth laws. It is also sufficient to reveal unknown features of cell growth previously unmeasurable. With these methodological and analytical improvements, we document a remarkable oscillation in growth rate in several different cell lines, occurring throughout the cell cycle, coupled to cell division or birth, and yet independent of cell cycle progression. We expect that further exploration with this improved tool will provide a better understanding of growth rate regulation in mammalian cells. Significance StatementIt has been a long-standing question in cell growth studies that whether the mass of individual cell grows linearly or exponentially. The two models imply fundamentally distinct mechanisms, and the discrimination of the two requires great measurement accuracy. Here, we develop a new method of computationally enhanced Quantitative Phase Microscopy (ceQPM), which greatly improves the accuracy and throughput of single-cell growth measurement in adherent mammalian cells. The measurements of several cell lines indicate that the growth dynamics of individual cells cannot be explained by either of the simple models but rather present an unanticipated and remarkable oscillatory behavior, suggesting more complex regulation and feedbacks.

systems biology↗

bioRxiv2019

The protein repertoire in early vertebrate embryogenesis

We present an unprecedentedly comprehensive characterization of protein dynamics across early development in Xenopus laevis, available immediately via a convenient Web portal. This resource allows interrogation of the protein expression data in conjunction with other data modalities such as genome wide mRNA expression. This study provides detailed data for absolute levels of [~]14K unique Xenopus proteins representing homologues of [~]9K unique human genes - a rich resource for developmental biologists. The purpose of this manuscript is limited to presenting and releasing the data browser.\n\nHighlightsO_LIRelative protein expression from stage IV oocyte, blastula, gastrula, neurula, and early organogenesis\nC_LIO_LIBiological triplicates with confidence intervals on protein expression reflect certainty in dynamic patterns\nC_LIO_LIConvenient time-series Web-browser integrated with the multi-media Xenbase portal\nC_LIO_LIGene-symbol search and multi-gene protein/mRNA juxtaposition capabilities\nC_LI

developmental biology↗

bioRxiv2018

YAP independently regulates cell size and population growth dynamics via non-cell autonomous mediators

The Hippo pathway, in which changes at the cell surface and in the extracellular environment control the activity of a downstream transcription factor, known as YAP in mammalian cells and Yorkie in Drosophila, has recently taken center-stage as perhaps the most important pathway in metazoans for controlling organ size. In intact tissues YAP activity is inhibited and the organ does not overgrow. When the organ is damaged, YAP is active and necessary for growth and regeneration to occur. The exact process by which YAP drives organ and tissue growth is not fully understood, although it is known to affect both cell size and cell number. Since cell size and proliferation are highly interdependent in many cultured cell studies, we investigated the role of YAP in the simultaneous regulation of both cell size and number. Our experiments reveal that YAP controls both cell size and cell proliferation by independent circuits, and that it affects each process non-cell autonomously via extracellular mediators. We identify that CYR61, a known secreted YAP target, is the major regulator of the non-cell autonomous increase in cell number, but does not affect cell size. The molecular identity of the non-cell autonomously acting mediator of cell size is yet to be identified.

cell biology↗

bioRxiv2018

The jellyfish genome sheds light on the early evolution of active predation

BackgroundUnique among cnidarians, jellyfish have remarkable morphological and biochemical innovations that allow them to actively hunt in the water column. One of the first animals to become free-swimming, jellyfish employ pulsed jet propulsion and venomous tentacles to capture prey.\n\nResultsTo understand these key innovations, we sequenced the genome of the giant Nomuras jellyfish (Nemopilema nomurai), the transcriptomes of its bell and tentacles, and transcriptomes across tissues and developmental stages of the Sanderia malayensis jellyfish. Analyses of Nemopilema and other cnidarian genomes revealed adaptations associated with swimming, marked by codon bias in muscle contraction and expansion of neurotransmitter genes, along with expanded Myosin type II family and venom domains; possibly contributing to jellyfish mobility and active predation. We also identified gene family expansions of Wnt and posterior Hox genes, and discovered the important role of retinoic acid signaling in this ancient lineage of metazoans, which together may be related to the unique jellyfish body plan (medusa formation).\n\nConclusionsTaken together, the jellyfish genome and transcriptomes genetically confirm their unique morphological and physiological traits that have combined to make these animals one of the worlds earliest and most successful multi-cellular predators.

genomics↗

bioRxiv2017

Mouse embryonic stem cells can differentiate via multiple paths to the same state

In embryonic development, cells must differentiate through stereotypical sequences of intermediate states to generate mature states of a particular fate. By contrast, direct programming can generate similar fates through alternative routes, by directly expressing terminal transcription factors. Yet the cell state transitions defining these new routes are unclear. We applied single-cell RNA sequencing to compare two mouse motor neuron differentiation protocols: a standard protocol approximating the embryonic lineage, and a direct programming method. Both undergo similar early neural commitment. Then, rather than transitioning through spinal intermediates like the standard protocol, the direct programming path diverges into a novel transitional state. This state has specific and abnormal gene expression. It opens a loop or worm hole in gene expression that converges separately onto the final motor neuron state of the standard path. Despite their different developmental histories, motor neurons from both protocols structurally, functionally, and transcriptionally resemble motor neurons from embryos.

developmental biology↗

bioRxiv2017

Cell size sensing in animal cells coordinates growth rates and cell cycle progression to maintain cell size uniformity

The uniformity of cell size in healthy tissues suggests that control mechanisms might coordinate cell growth and division. We derived a method to assay whether growth rates of individual cells depend on cell size, by combining time-lapse microscopy and immunofluorescence to monitor how variance in cell size changes as cells grow. This analysis revealed two periods in the cell cycle when cell size variance decreases in a manner incompatible with unregulated growth, suggesting that cells sense their own size and adjust their growth rate to correct aberrations. Monitoring nuclear growth in live cells confirmed that these decreases in variance reflect a process that selectively inhibits the growth of large cells while accelerating growth of small cells. We also detected cell-size-dependent adjustments of G1 length, which further reduce variability. Combining our assays with chemical and genetic perturbations confirmed that cells employ two strategies, adjusting both cell cycle length and growth rate, to maintain the appropriate size.

cell biology↗

bioRxiv2017

Size uniformity of animal cells is actively maintained by a p38 MAPK-dependent regulation of G1-length

Animal cells within a tissue typically display a striking regularity in their size. To date, the molecular mechanisms that control this uniformity are still unknown. We have previously shown that size uniformity in animal cells is promoted, in part, by size-dependent regulation of G1 length. To identify the molecular mechanisms underlying this process, we performed a large-scale small molecule screen and found that the p38 MAPK pathway is involved in coordinating cell size and cell cycle progression. Small cells display higher p38 activity and spend more time in G1 than larger cells. Inhibition of p38 MAPK leads to loss of the compensatory G1 length extension in small cells, resulting in faster proliferation, smaller cell size and increased size heterogeneity. We propose a model wherein the p38 pathway responds to changes in cell size and regulates G1 exit accordingly, to increase cell size uniformity.\n\nOne-sentence summaryThe p38 MAP kinase pathway coordinates cell growth and cell cycle progression by lengthening G1 in small cells, allowing them more time to grow before their next division.

cell biology↗

bioRxiv2016

Conformational landscape of the p28-bound human proteasome regulatory particle

The proteasome holoenzyme is activated by its regulatory particle (RP) consisting of two subcomplexes, the lid and the base. A key event in base assembly is the formation of a heterohexameric ring of AAA-ATPases, which is guided by at least four RP assembly chaperones in mammals: PAAF1, p28/gankyrin, p27/PSMD9 and S5b. We determined a cryo-EM structure of the human RP in complex with its assembly chaperone p28 at 4.5-[A] resolution. The Rpn1-p28-AAA subcomplex in the p28-bound RP is highly dynamic and was resolved to subnanometer resolution in seven states, which recapitulate the conformational landscape of the complex. Surprisingly, the p28-bound AAA ring does not form a channel in the free RP. Instead, it spontaneously samples multiple open and closed topologies. Our analysis suggests that p28 guides the proteolytic core particle to select certain conformation of the ATPase ring for RP engagement in the last step of the chaperone-mediated proteasome assembly.

biochemistry↗