N2FXm, a method for joint nuclear and cytoplasmic volume measurements, unravels the osmo-mechanical regulation of nuclear volume in mammalian cells.

In eukaryotes, cytoplasmic and nuclear volumes are tightly regulated to ensure proper cell homeostasis. However, current methods to measure cytoplasmic and nuclear volumes, including confocal 3D reconstruction, have limitations, such as relying on two-dimensional projections or poor vertical resolution. Here, to overcome these limitations, we describe a method, N2FXm, to jointly measure cytoplasmic and nuclear volumes in single cultured adhering human cells, in real time, and across cell cycles. We find that this method accurately provides joint size over dynamic measurements and at different time resolutions. Moreover, by combining several experimental perturbations and analyzing a mathematical model including osmotic effects and tension, we show that N2FXm can give relevant insights on how mechanical forces exerted by the cytoskeleton on the nuclear envelope can affect the growth of nucleus volume by biasing nuclear import. Our method, by allowing for accurate joint nuclear and cytoplasmic volume dynamic measurements at different time resolutions, highlights the non-constancy of the nucleus/cytoplasm ratio along the cell cycle.

Leveraging Tissue-Specific Enhancer-Target Gene Regulatory Networks Identifies Enhancer Somatic Mutations That Functionally Impact Lung Cancer.

Enhancers are noncoding regulatory DNA regions that modulate the transcription of target genes, often over large distances along with the genomic sequence. Enhancer alterations have been associated with various pathological conditions, including cancer. However, the identification and characterization of somatic mutations in noncoding regulatory regions with a functional effect on tumorigenesis and prognosis remain a major challenge. Here, we present a strategy for detecting and characterizing enhancer mutations in a genome-wide analysis of patient cohorts, across three lung cancer subtypes. Lung tissue-specific enhancers were defined by integrating experimental data and public epigenomic profiles, and the genome-wide enhancer-target gene regulatory network of lung cells was constructed by integrating chromatin three-dimensional architecture data. Lung cancers possessed a similar mutation burden at tissue-specific enhancers and exons but with differences in their mutation signatures. Functionally relevant alterations were prioritized on the basis of the pathway-level integration of the effect of a mutation and the frequency of mutations on individual enhancers. The genes enriched for mutated enhancers converged on the regulation of key biological processes and pathways relevant to tumor biology. Recurrent mutations in individual enhancers also affected the expression of target genes, with potential relevance for patient prognosis. Together, these findings show that noncoding regulatory mutations have a potential relevance for cancer pathogenesis and can be exploited for patient classification. SIGNIFICANCE: Mapping enhancer-target gene regulatory interactions and analyzing enhancer mutations at the level of their target genes and pathways reveal convergence of recurrent enhancer mutations on biological processes involved in tumorigenesis and prognosis.

SELENON (SEPN1) protects skeletal muscle from saturated fatty acid-induced ER stress and insulin resistance.

Selenoprotein N (SELENON) is an endoplasmic reticulum (ER) protein whose loss of function leads to a congenital myopathy associated with insulin resistance (SEPN1-related myopathy). The exact cause of the insulin resistance in patients with SELENON loss of function is not known. Skeletal muscle is the main contributor to insulin-mediated glucose uptake, and a defect in this muscle-related mechanism triggers insulin resistance and glucose intolerance. We have studied the chain of events that connect the loss of SELENON with defects in insulin-mediated glucose uptake in muscle cells and the effects of this on muscle performance. Here, we show that saturated fatty acids are more lipotoxic in SELENON-devoid cells, and blunt the insulin-mediated glucose uptake of SELENON-devoid myotubes by increasing ER stress and mounting a maladaptive ER stress response. Furthermore, the hind limb skeletal muscles of SELENON KO mice fed a high-fat diet mirrors the features of saturated fatty acid-treated myotubes, and show signs of myopathy with a compromised force production. These findings suggest that the absence of SELENON together with a high-fat dietary regimen increases susceptibility to insulin resistance by triggering a chronic ER stress in skeletal muscle and muscle weakness. Importantly, our findings suggest that environmental cues eliciting ER stress in skeletal muscle (such as a high-fat diet) affect the pathological phenotype of SEPN1-related myopathy and can therefore contribute to the assessment of prognosis beyond simple genotype-phenotype correlations.

A monoclonal antibody specific for prophase phosphorylation of histone deacetylase 1: a readout for early mitotic cells.

Histone deacetylases (HDACs) are modification enzymes that regulate a plethora of biological processes. HDAC1, a crucial epigenetic modifier, is deregulated in cancer and subjected to a variety of post-translational modifications. Here, we describe the generation of a new monoclonal antibody that specifically recognizes a novel highly dynamic prophase phosphorylation of serine 406-HDAC1, providing a powerful tool for detecting early mitotic cells.

A monoclonal antibody against mutated nucleophosmin 1 for the molecular diagnosis of acute myeloid leukemias.

Mutations in the nucleophosmin 1 (NPM1) gene are the most frequent genetic aberrations of acute myeloid leukemia (AML) and define a clinically distinct subset of AML. A monoclonal antibody (T26) was raised against a 19-amino acid polypeptide containing the unique C-terminus of the type A NPM1 mutant protein. T26 recognized 10 of the 21 known NPM1 mutants, including the A, B, and D types, which cover approximately 95% of all cases, and did not cross-react with wild-type NPM1 or unrelated cellular proteins. It performed efficiently with different detection technologies, including immunofluorescence, immunohistochemistry, and flow cytometry. Within a series of consecutive de novo AML patients, 44 of 110 (40%) and 15 of 39 (38%) cases scored positive using the T26 antibody in immunofluorescence and flow cytometry assays, respectively. T26-positive cases were found to be all carrying mutations of NPM1 exclusively, as determined by molecular analysis. T26 is the first antibody that specifically recognizes a leukemia-associated mutant protein. Immunofluorescence or flow cytometry using T26 may thus become a new tool for a rapid, simple, and cost-effective molecular diagnosis of AMLs.

Monoclonal antibodies isolated by large-scale screening are suitable for labeling adult zebrafish (Danio rerio) tissues and cell structures.

The lack of a sufficient number of antibodies represents an obstacle in the research performed using the zebrafish (Danio rerio) as a model organism. On the other hand, high-throughput generation of antibodies, especially those suitable for immunohistochemistry, is not an established methodology. Here we present the results of an immunization experiment with a zebrafish tissue lysate that allowed for the isolation of hundreds of monoclonal antibodies suitable for labeling of a large variety of zebrafish tissue and cell structures. Some of them were further characterized in terms of detailed localization and age-dependent expression. In addition, the antigen recognized by one of them was first immunoprecipitated and then identified by mass spectrometry. Furthermore, immunofluorescence-competent recombinant antibodies were also isolated by panning large repertoire phage display libraries, in both single-chain (scFv) and single-domain (VHH) format. Such selection alternative is simpler to organize and could contribute to limit the costs of antibody screening and production.