Biology subjects

Jacobson, E. C.

Publications and source records attributed to Jacobson, E. C..

4 recordsLinked to original sources

bioRxiv2020

Xist-seeded nucleation sites form local concentration gradients of silencing proteins to inactivate the X-chromosome

The long non-coding RNA Xist exploits numerous effector proteins to progressively induce gene silencing across the X chromosome and form the inactive X (Xi)-compartment. The mechanism underlying formation of the chromosome-wide Xi-compartment is poorly understood. Here, we find that formation of the Xi-compartment is induced by [~]50 locally confined granules, where two Xist RNA molecules nucleate supra-molecular complexes (SMCs) of interacting proteins. Xist-SMCs are transient structures that concentrate rapidly recycling proteins in the X by increasing protein binding affinity. We find that gene silencing originates at Xist-SMCs and propagates across the entire chromosome over time, achieved by Polycomb-mediated coalescence of chromatin regions and aggregation, via its intrinsically disordered domains, of the critical silencing factor SPEN. Our results suggest a new model for X chromosome inactivation, in which Xist RNA induces macromolecular crowding of heterochromatinizing proteins near distinct sites which ultimately increases their density throughout the chromosome. This mechanism enables deterministic gene silencing without the need for Xist ribonucleoprotein complex-chromatin interactions at each target gene.

cell biology↗

bioRxiv2018

Hi-C detects novel structural variants in HL-60 and HL-60/S4 cell lines

Cancer cell lines often have large structural variants (SVs) that evolve over time. There are many reported differences in large scale SVs between HL-60 and HL-60/S4, cell lines derived from the same acute promyelocytic leukemia sample. However, the stability and variability of inter- and intra-chromosomal SVs between different sources is unknown. Here, we used Hi-C and RNA-seq to identify and compare large SVs in HL-60 and HL-60/S4 cell lines.\n\nComparisons with previously reported karyotypes identified two non-canonical SVs in HL-60. Ten previously unreported SVs were identified in HL-60/S4. The unreported SVs were generally small enough to be plausibly undetected with traditional karyotyping methods. An expansion centered on MYC was found in a novel genomic location in HL-60. The HL-60 cell line has more within-line structural variation than the HL-60/S4 derivative cell line.\n\nHL-60 and HL-60/S4 karyotypes are generally consistent with the current literature, with some exceptions. Hic_breakfinder is an effective tool for identifying all SVs, but intra-chromosomal SVs are less reliably detected across different samples. The orientation of SV patterns, and strandedness of gene fusions, allowed us to differentiate inversions from other forms of intra-chromosomal SV. Visual inspection of Hi-C heatmap patterns allow further characterization of SVs without additional methods, although orthogonal information such as gene fusions contribute to the characterization.

genomics↗

bioRxiv2018

TNF-α differentially regulates cell cycle genes in promyelocytic and granulocytic HL-60/S4 cells

Tumor necrosis factor alpha (TNF-) is a potent cytokine involved in systemic inflammation and immune modulation. Signaling responses that involve TNF- are context dependent and capable of stimulating pathways promoting both cell death and survival. TNF- treatment has been investigated as part of a combined therapy for acute myeloid leukemia due to its modifying effects on all-trans retinoic acid (ATRA) mediated differentiation into granulocytes.\n\nTo investigate the interaction between cellular differentiation and TNF-, we performed RNA-sequencing on two forms of the human HL-60/S4 promyelocytic leukemia cell line treated with TNF-. The ATRA-differentiated granulocytic form of HL-60/S4 cells had an enhanced transcriptional response to TNF- treatment compared to the undifferentiated promyelocytes. The observed TNF- responses included differential expression of cell cycle gene sets, which were generally upregulated in TNF- treated promyelocytes, and downregulated in TNF- treated granulocytes. This is consistent with TNF- induced cell cycle repression in granulocytes and cell cycle progression in promyelocytes. Moreover, comparisons with gene expression changes associated with differentiation indicated that TNF- treatment of granulocytes shifts the transcriptome towards that of a macrophage.\n\nWe conclude that TNF- treatment promotes a divergent transcriptional program in promyelocytes and granulocytes. TNF- promotes cell cycle associated gene expression in promyelocytes. In contrast, TNF- stimulated granulocytes have reduced cell cycle gene expression, and a macrophage-like transcriptional program.

genomics↗

bioRxiv2018

Migration through a small pore disrupts inactive chromatin organisation in neutrophil-like cells

BackgroundMammalian cells are flexible and can rapidly change shape when they contract, adhere, or migrate. Their nucleus must be stiff enough to withstand cytoskeletal forces, but flexible enough to remodel as the cell changes shape. This is particularly important for cells migrating through constricted space, where the nuclear shape must change in order to fit through the constriction. This occurs many times in the life cycle of a neutrophil, which must protect its chromatin from damage and disruption associated with migration.\n\nResultsTotal RNA-sequencing identified that neutrophil migration through 5 or 14m pores was associated with changes in the transcript levels of inflammation and chemotaxis-related genes, when compared to unmigrated cells. Differentially expressed transcripts specific to migration with constriction were enriched for groups of genes associated with cytoskeletal remodeling.\n\nHi-C was used to capture the genome organization in control and migrated cells. Minimal switching was observed between the active (A) and inactive (B) compartments after migration. However, global depletion of short range contacts was observed following migration with constriction compared to migration without constriction. Regions with disrupted contacts, TADs, and compartments were enriched for inactive chromatin.\n\nConclusionShort range genome organization is preferentially altered in inactive chromatin, possibly protecting transcriptionally active contacts from the disruptive effects of migration with constriction. This is consistent with current hypotheses implicating heterochromatin as the mechanoresponsive form of chromatin. Further investigation concerning the contribution of heterochromatin to stiffness, flexibility, and protection of nuclear function will be important for understanding cell migration in human health and disease.

genomics↗