Biology subjects

Lippincott-Schwartz, J.

Publications and source records attributed to Lippincott-Schwartz, J..

44 records · Page 3Linked to original sources

bioRxiv2019

Spastin tethers lipid droplets to peroxisomes and directs fatty acid trafficking through ESCRT-III

Lipid droplets (LDs) are neutral lipid storage organelles that transfer lipids to various organelles including peroxisomes. Here, we show that the hereditary spastic paraplegia protein M1 Spastin, a membrane-bound AAA ATPase found on LDs, coordinates fatty acid (FA) trafficking from LDs to peroxisomes through two inter-related mechanisms. First, M1 Spastin forms a tethering complex with peroxisomal ABCD1 to promote LD-peroxisome contact formation. Second, M1 Spastin recruits the membrane-shaping ESCRT-III proteins IST1 and CHMP1B to LDs via its MIT domain to facilitate LD-to-peroxisome FA trafficking, possibly through IST1 and CHMP1B modifying LD membrane morphology. Furthermore, M1 Spastin, IST1 and CHMP1B are all required to relieve LDs of lipid peroxidation. M1 Spastins dual roles in tethering LDs to peroxisomes and in recruiting ESCRT-components to LD-peroxisome contact sites for FA trafficking may help explain the pathogenesis of diseases associated with defective FA metabolism in LDs and peroxisomes.

cell biology↗

bioRxiv2019

Fate plasticity and reprogramming in genetically distinct populations of Danio leucophores

Understanding genetic and cellular bases of adult form remains a fundamental goal at the intersection of developmental and evolutionary biology. The skin pigment cells of vertebrates, derived from embryonic neural crest, are a useful system for elucidating mechanisms of fate specification, pattern formation, and how particular phenotypes impact organismal behavior and ecology. In a survey of Danio fishes, including zebrafish Danio rerio, we identified two populations of white pigment cells--leucophores--one of which arises by transdifferentiation of adult melanophores and another that develops from a yellow/orange xanthophore-like progenitor. Single-cell transcriptomic, mutational, chemical and ultrastructural analyses of zebrafish leucophores revealed cell-type specific chemical compositions, organelle configurations and genetic requirements. At the organismal level, we identified distinct physiological responses of leucophores during environmental background matching and we show that leucophore complement influences behavior. Together, our studies revealed new, independently arisen pigment cell types and mechanisms of fate acquisition in zebrafish, and illustrate how concerted analyses across hierarchical levels can provide insights into phenotypes and their evolution.

developmental biology↗

bioRxiv2018

Cytoplasmic self-organization established by internal lipid membranes in the interplay with either actin or microtubules

Cells harbor an intrinsic organization of their components. Specific protein structures, as the centrosome, have been described master regulators of cell organization. In the absence of these key elements, however, cytoplasmic selforganization has nevertheless been observed. Cytoplasmic self-organization was postulated to arise from the interaction of microtubules with molecular motors on lipid membrane surfaces.\n\nHere, we show that lipid membranes are capable of organizing both major cytoskeletal systems, microtubules and actin, even if one or the other cytoskeletal system is completely paralyzed. A microfluidic droplet system and Xenopus oocyte extracts enabled us to build an artificial cell and study minimal requirements for cellular self-organization. Mathematical modeling reveals the interaction of lipid membranes with any filament system through molecular motors as a universal principle of cytoplasmic self-organization. Both cytoskeletal systems form mechanisms to establish robust 2-dimensional selforganization and self-centering. Pharmacologic inhibition of the cytoskeletal network systems helps dissect specific contributions of each network in the interplay with lipid membranes with regards to 2- and 3-dimensional organization, time and length scale of cytoplasmic organization and the degree of concentration of the centered elements. While microtubules provide 3-dimensional polarity, actin filaments ensure fast and dense compaction and long-range organization.

cell biology↗

bioRxiv2018

Neuron-astrocyte metabolic coupling during neuronal stimulation protects against fatty acid toxicity

GRAPHICAL ABSTACT\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=165 SRC=\"FIGDIR/small/465237_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (57K):\norg.highwire.dtl.DTLVardef@1d6cbf4org.highwire.dtl.DTLVardef@e83c9corg.highwire.dtl.DTLVardef@e35b92org.highwire.dtl.DTLVardef@910303_HPS_FORMAT_FIGEXP M_FIG C_FIG HIGHLIGHTSO_LIHyperactive neurons generate and release excess peroxidated fatty acids (FAs)\nC_LIO_LIAstrocytes endocytose toxic FAs as lipoprotein particles, delivering them to lipid droplets\nC_LIO_LILipid droplets trigger upregulation of genes involved in metabolism and detoxification\nC_LIO_LIAstrocytes detoxify and consume FAs by mitochondrial oxidation in response to neural activity\nC_LI\n\nSUMMARYMetabolic coordination between neurons and astrocytes is critical for the health of the brain. However, neuron-astrocyte coupling of lipid metabolism, particularly in response to neural activity, remains largely uncharacterized. Here, we demonstrate that toxic, peroxidated fatty acids (FAs) produced in hyperactive neurons are transferred to astrocytic lipid droplets by lipoprotein particles. Astrocytes consume the FAs stored in lipid droplets via mitochondrial {beta}-oxidation in response to neuronal activity and turn on a detoxification gene expression program. Together, our findings reveal that FA metabolism between neurons and astrocytes is coupled in an activity-dependent manner to protect neurons from FA toxicity. This coordinated mechanism for metabolizing FAs could underlie both homeostasis and a variety of disease states of the brain.

neuroscience↗

bioRxiv2018

Phase Separation of YAP Reprograms Cells for Long-term YAP Target Gene Expression

Yes-associated Protein (YAP) is a transcriptional co-activator that regulates cell proliferation and survival by binding to a selective set of enhancers for potent target gene activation, but how YAP coordinates these transcriptional responses is unknown. Here, we demonstrate that YAP forms liquid-like condensates in the nucleus in response to macromolecular crowding. Formed within seconds of hyperosmotic stress, YAP condensates compartmentalized YAPs DNA binding cofactor TEAD1 along with other YAP-related transcription co-activators, including TAZ, and subsequently induced transcription of YAP-specific proliferation genes. Super-resolution imaging using Assay for Transposase Accessible Chromatin with photoactivated localization microscopy (ATAC-PALM) revealed that YAP nuclear condensates were areas enriched in accessible chromatin domains organized as super-enhancers. Initially devoid of RNA Polymerase II (Pol II), the accessible chromatin domains later acquired Pol II, producing newly transcribed RNA. Removal of YAPs intrinsically-disordered transcription activation domain (TAD) prevented YAP condensate formation and diminished downstream YAP signaling. Thus, dynamic changes in genome organization and gene activation during YAP reprogramming is mediated by liquid-liquid phase separation.

cell biology↗

bioRxiv2018

Cortical Column and Whole Brain Imaging of Neural Circuits with Molecular Contrast and Nanoscale Resolution

Optical and electron microscopy have made tremendous inroads in understanding the complexity of the brain, but the former offers insufficient resolution to reveal subcellular details and the latter lacks the throughput and molecular contrast to visualize specific molecular constituents over mm-scale or larger dimensions. We combined expansion microscopy and lattice light sheet microscopy to image the nanoscale spatial relationships between proteins across the thickness of the mouse cortex or the entire Drosophila brain, including synaptic proteins at dendritic spines, myelination along axons, and presynaptic densities at dopaminergic neurons in every fly neuropil domain. The technology should enable statistically rich, large scale studies of neural development, sexual dimorphism, degree of stereotypy, and structural correlations to behavior or neural activity, all with molecular contrast.\n\nOne Sentence SummaryCombined expansion and lattice light sheet microscopy enables high speed, nanoscale molecular imaging of neural circuits over large volumes.

neuroscience↗

bioRxiv2018

mTOR-dependent phosphorylation controls TFEB nuclear export

The transcriptional activation of catabolic processes during starvation is induced by the nuclear translocation and consequent activation of transcription factor EB (TFEB), a master modulator of autophagy and lysosomal biogenesis. However, how TFEB is inactivated upon nutrient re-feeding is currently unknown. Here we show that TFEB subcellular localization is dynamically controlled by its continuous shuttling between the cytosol and the nucleus, with the nuclear export representing a limiting step. TFEB nuclear export is mediated by CRM1 and is modulated by nutrient availability via mTOR-dependent hierarchical multisite phosphorylation of serines S142 and S138, which are localized in proximity of a nuclear export signal (NES). Our data reveal that modulation of TFEB nuclear export via phosphorylation plays a major role in the modulation of TFEB localization and activity.

cell biology↗

bioRxiv2017

Immature HIV-1 Lattice Assembly Dynamics are Regulated by Scaffolding from Nucleic Acid and the Plasma Membrane

The packaging and budding of Gag polyprotein and viral ribonucleic acid (RNA) is a critical step in the human immunodeficiency virus-1 (HIV-1) lifecycle. High-resolution structures of the Gag polyprotein have revealed that the capsid (CA) and spacer peptide 1 (SP1) domains contain important interfaces for Gag self-assembly. However, the molecular details of the multimerization process, especially in the presence of RNA and the cell membrane, have remained unclear. In this work, we investigate the mechanisms that work in concert between the polyproteins, RNA, and membrane to promote immature lattice growth. We develop a coarse-grained (CG) computational model that is derived from sub-nanometer resolution structural data. Our simulations recapitulate contiguous and hexameric lattice assembly driven only by weak anisotropic attractions at the helical CA-SP1 junction. Importantly, analysis from CG and single-particle tracking photoactivated localization (spt-PALM) trajectories indicates that viral RNA and the membrane are critical constituents that actively promote Gag multimerization through scaffolding, while over-expression of short competitor RNA can suppress assembly. We also find that the CA amino-terminal domain imparts intrinsic curvature to the Gag lattice. As a consequence, immature lattice growth appears to be coupled to the dynamics of spontaneous membrane deformation. Our findings elucidate a simple network of interactions that regulate the early stages of HIV-1 assembly and budding.\n\nSIGNIFICANCE STATEMENTIn order for human immunodeficiency virus to proliferate, viral proteins and genomic dimers are assembled at host cell membranes and released as immature virions. Disrupting this key intermediate step in viral replication is a potential target for treatment. However, a detailed molecular view of this process remains lacking. Here, we elucidate a network of constitutive interactions that regulate viral assembly dynamics through a combined computational and experimental approach. Specifically, our analysis reveals the active roles of nucleic acid and the membrane as scaffolds that promote the multimerization of Gag polyprotein which proceeds through multi-step and self-correcting nucleation. Our findings also illustrate the functional importance of the N-terminal, C-terminal, and spacer peptide 1 protein domains.

biophysics↗