Biology subjects

Losada, A.

Publications and source records attributed to Losada, A..

11 recordsLinked to original sources

bioRxiv2026

Nuclear blebs are composed of variable chromatin states but consistently enrich transcription initiation relative to elongation

Nuclear blebs are herniations of the nucleus that occur in many human conditions including aging, heart disease, muscular dystrophy, and many cancers. Nuclear blebbing causes nuclear rupture and cellular dysfunction. However, understanding the formation, stability, and identification of nuclear blebs remains an ongoing challenge. Our previous studies reveal that nuclear blebs are best hallmarked by decreased DNA density. To determine if chromatin decompaction underlies decreased DNA density in nuclear blebs, we investigated the histone composition of nuclear blebs across multiple cell lines. Time lapse and immunofluorescence imaging revealed that global histone H2B and H3 levels are decreased in the nuclear bleb relative to the nuclear body. Next, we imaged histone modification states of euchromatin and heterochromatin, which respectively track decompact and compact states of chromatin. Overall, we find that nuclear blebs display variable histone modification state across cell lines, as euchromatin does not consistently enrich nor is heterochromatin consistently depleted. Nuclear blebs did consistently show active RNA Pol II initiation is enriched relative to elongation. Thus, we find that the local histone modification state is not an essential component of nuclear blebs while transcription initiation enrichment over elongation is reproducible across cell lines and conditions. Summary statementWe measured histones and their modification states in nuclear blebs. We find that chromatin state is variable while transcription initiation is consistently enriched relative to elongation in nuclear blebs.

cell biology↗

bioRxiv2025

Integrative multi-omics reveals PARP14 as a key IFNγ-regulated mediator of metastatic progression in Ewing sarcoma.

Metastatic Ewing sarcoma (EwS) remains a major clinical challenge, highlighting the need to identify molecular drivers of disease dissemination. Through integrated transcriptomic, functional, and mechanistic analyses, we identify PARP14 as a key regulator of EwS metastatic progression. PARP14 is consistently upregulated in metastatic lesions across spontaneous and xenograft mouse models as well as in patient samples. Genetic and pharmacologic depletion of PARP14 (via siRNA knockdown, CRISPR-Cas9 knockout, or PROTAC-mediated degradation) significantly impaired EwS cell migration and invasion in vitro, without affecting proliferation or clonogenic capacity. In vivo, PARP14 loss delayed tumor growth and reduced metastatic burden, supporting a functional role in disease progression. Conversely, IFN{gamma}-induced PARP14 upregulation and stable overexpression enhanced EwS cell migration and increased lung metastasis formation. Transcriptomic profiling of PARP14-deficient cells revealed downregulation of invasive signatures and enrichment of inflammatory and p53-related pathways, together with gene sets associated with chromatin remodeling. Subcellular fractionation and interactome analyses showed that PARP14 localizes to cytoplasmic, nuclear, and chromatin-associated compartments, and interacts with chromatin, cytoskeletal and ECM regulators. ChlP analyses further demonstrated PARP14 binding to promoters enriched for NRF1 motifs, suggesting a role as a transcriptional co-regulator influencing gene networks relevant to EwS progression. Together, our results establish PARP14 as a contributor to EwS dissemination and uncover a previously unappreciated chromatin-associated role for this protein, supporting its potential as both a biomarker and therapeutic target in metastatic EwS. STATEMENT OF SIGNIFICANCEWe identify PARP14 as a novel driver of Ewing sarcoma metastasis through integrated multi-omics profiling. Genetic and pharmacological interrogation establishes PARP14 as a promising therapeutic target for this understudied malignancy.

cancer biology↗

bioRxiv2025

AT-hook-dependent DNA loop extrusion by STAG1 drives 3D genome folding

Cohesin, a ring-shaped complex composed of Smc1, Smc3, Scc1 and STAG, is essential for sister chromatid cohesion and the regulation of three-dimensional (3D) genome architecture. At the single-molecule level, cohesin extrudes DNA loops, a process thought to drive higher-order genome folding. In vertebrates, cohesin incorporates either STAG1 or STAG2. Although both support sister chromatid cohesion, they differentially regulate 3D genome organization. However, the mechanistic basis for these differences has remained unclear. Here we show, using single-molecule assays, that cohesin-STAG1 extrudes DNA loops more efficiently than cohesin-STAG2, despite comparable ATPase activity and topological DNA entrapment. We identify an AT-hook motif unique to the STAG1 N-terminus as the element that promotes loop extrusion without altering ATPase activity or DNA binding. In human somatic cells, the AT-hook is required for stable cohesin-chromatin association during G1 phase but is dispensable for sister chromatid cohesion. Mutation of this motif markedly impairs TAD and chromatin loop formation. These findings highlight AT-hook as a critical determinant that distinguishes STAG1 from STAG2 by promoting DNA loop extrusion and stabilizing cohesin-chromatin interactions in interphase through a mechanism distinct from the one underlying sister chromatid cohesion.

molecular biology↗

bioRxiv2024

A comprehensive genetic catalog of human double-strand break repair

The analysis of DNA sequence outcomes provides molecular insights into double-strand break (DSB) repair mechanisms. By employing parallel in-pool profiling of Cas9-induced indels within a genome-wide knockout library, we present a comprehensive catalog detailing how virtually every human gene influences the DSB repair process. This REPAIRome resource is validated through the identification of novel mechanisms, pathways and factors involved in DSB repair, including unexpected opposing roles for XLF and PAXX in DNA end processing, a molecular explanation for Cas9-induced multi-nucleotide insertions, the identification of HLTF as a DSB-repair factor, the involvement of the SAGA complex in microhomology-mediated end joining, and importantly, an indel mutational signature linked to VHL loss, renal carcinoma and hypoxia. Collectively, these results exemplify the potential of REPAIRome to drive future discoveries in DSB repair, CRISPR-Cas gene editing and the etiology of cancer mutational signatures.

molecular biology↗

bioRxiv2024

miR-203 controls timing of developmental transitions during early preimplantation embryogenesis

Commonly expressed at developmental transitions, microRNAs operate as fine tuners of gene expression to facilitate cell fate acquisition and lineage segregation. Nevertheless, how they might regulate the earliest developmental transitions in early mammalian embryogenesis remains obscure. Here, in a strictly in vivo approach based on novel genetically-engineered mouse models and single-cell RNA sequencing, we identify miR-203 as a critical regulator of timing and cell fate restriction within the totipotency to pluripotency transition in mouse embryos. Genetically engineered mouse models show that loss of miR-203 slows down developmental timing during preimplantation leading to the accumulation of embryos with high expression of totipotency-associated markers, including MERVL endogenous retroviral elements. A new embryonic reporter (eE-Reporter) transgenic mouse carrying MERVL-Tomato and Sox2-GFP transgenes showed that lack of miR-203 leads to sustained expression of MERVL and reduced Sox2 expression in preimplantation developmental stages. A combination of single-cell transcriptional studies and epigenetic analyses identified the central coactivator and histone acetyltransferase P300 as a major miR-203 target at the totipotency to pluripotency transition in vivo. By fine tuning P300 levels, miR-203 carves the epigenetic rewiring process needed for this developmental transition, allowing a timely and correctly paced development.

developmental biology↗

bioRxiv2022

Different NIPBL requirements of cohesin-STAG1 and cohesin-STAG2

Cohesin organizes the genome through the formation of chromatin loops. NIPBL activates cohesins ATPase and is essential for loop extrusion, but its requirement for cohesin loading is currently unclear. Here we have examined the effect of reducing NIPBL levels on the behavior of the two cohesin variants carrying STAG1 or STAG2 by combining a flow cytometry assay to measure chromatin-bound cohesin with analyses of its genome-wide distribution and genome contacts. We show that NIPBL depletion results in increased cohesin-STAG1 on chromatin that further accumulates at CTCF positions while cohesin-STAG2 diminishes genome-wide. Our data support a model in which NIPBL is not required for initial association of cohesin with chromatin but it is for loop extrusion, which in turn facilitates stabilization of cohesin-STAG2 at CTCF positions after being loaded elsewhere. In contrast, cohesin-STAG1 is loaded and stabilized at CTCF sites even under low NIPBL levels, but genome folding is severely impaired.

cell biology↗

bioRxiv2021

Unraveling the antiviral activity of plitidepsin by subcellular and morphological analysis

The pandemic caused by the new coronavirus SARS-CoV-2 has made evident the need for broad-spectrum, efficient antiviral treatments to combat emerging and re-emerging viruses. Plitidepsin is an antitumor agent of marine origin that has also shown a potent pre-clinical efficacy against SARS-CoV-2. Plitidepsin targets the host protein eEF1A (eukaryotic translation factor 1 alpha 1) and affects viral infection at an early, post-entry step. Because electron microscopy is a valuable tool to study virus-cell interactions and the mechanism of action of antiviral drugs, in this work we have used transmission electron microscopy (TEM) to evaluate the effects of plitidepsin in SARS-CoV-2 infection in cultured Vero E6 cells 24 and 48h post-infection. In the absence of plitidepsin, TEM morphological analysis showed double-membrane vesicles (DMVs), organelles that support coronavirus genome replication, single-membrane vesicles with viral particles, large vacuoles with groups of viruses and numerous extracellular virions attached to the plasma membrane. When treated with plitidepsin, no viral structures were found in SARS-CoV-2-infected Vero E6 cells. Immunogold detection of SARS-CoV-2 nucleocapsid (N) protein and double-stranded RNA (dsRNA) provided clear signals in cells infected in the absence of plitidepsin, but complete absence in cells infected and treated with plitidepsin. The present study shows that plitidepsin completely blocks the biogenesis of viral replication organelles and the morphogenesis of virus progeny. Electron microscopy morphological analysis coupled to immunogold labeling of SARS-CoV-2 products offers a unique approach to understand how antivirals such as plitidepsin work.

microbiology↗

bioRxiv2021

Establishment of 3D chromatin structure after fertilization and the metabolic switch at the morula-to-blastocyst transition require CTCF

The eukaryotic genome is tightly packed inside the nucleus, where it is organized in 3D at different scales. This structure is driven and maintained by different chromatin states and by architectural factors that bind DNA, such as the multi-zinc finger protein CTCF. Zygotic genome structure is established de novo after fertilization, but the impact of such structure on genome function during the first stages of mammalian development is still unclear. Here, we show that deletion of the Ctcf gene in mouse embryos impairs the correct establishment of chromatin structure, but initial lineage decisions take place and embryos are viable until the late blastocyst stage. Furthermore, we observe that maternal CTCF is not necessary for development. Transcriptomic analyses of mutant embryos show that the changes in metabolic and protein homeostasis programs that occur during the progression from the morula to the blastocyst depend on CTCF. Yet, these changes in gene expression do not correlate with disruption of chromatin structure, but mainly with proximal binding of CTCF to the promoter region of genes downregulated in mutants. Our results show that CTCF regulates both 3D genome organization and transcription during mouse preimplantation development, but mostly as independent processes.

developmental biology↗

bioRxiv2019

STAG2 cohesin is essential for heart morphogenesis

The distinct functions of cohesin complexes carrying STAG1 or STAG2 need to be unraveled. STAG2 is commonly mutated in cancer and germline mutations have been identified in cohesinopathy patients. To better understand the underlying pathogenic mechanisms, we here report the consequence of Stag2 ablation in mice. STAG2 is largely dispensable in adults and its tissue-wide inactivation does not lead to tumors but reduces fitness and affects both hematopoiesis and intestinal homeostasis. STAG2 is also dispensable for murine embryonic fibroblasts in vitro. In contrast, null embryos die by mid gestation showing global developmental delay and heart defects. Histopathological analysis and RNA-sequencing unveiled that STAG2 is required both for proliferation and regulation of cardiac transcriptional programs and in its absence, secondary heart field progenitors fail to enter the heart tube. These results provide compelling evidence on cell- and tissue-specific roles of the two cohesin complexes and how their dysfunction contributes to disease.

developmental biology↗

bioRxiv2019

PDS5 proteins regulate the length of axial elements and telomere integrity during male mouse meiosis

Cohesin cofactors regulate the loading, maintenance and release of cohesin complexes from chromosomes during the mitotic cell cycle but little is known on their role during vertebrate meiosis. One such cofactor is PDS5, which exists in two versions in somatic and germline cells, PDS5A and PDS5B, with unclear functional specificity. Here we have analyzed their distribution and functions in mouse spermatocytes. We show that simultaneous elimination of PDS5A and PDS5B results in severe defects during prophase I while their individual depletion does not, suggesting a functional redundancy of the two factors. Shortened axial/lateral elements and a reduction of early recombination nodules are observed in the absence of both PDS5 proteins. Moreover, telomere integrity and their association to the nuclear envelope are severely compromised. As these defects occur without detectable reduction in chromosome-bound cohesin, we propose that the dynamic behavior of the complex, mediated by PDS5 proteins, is key for successful completion of meiotic prophase I.

cell biology↗

bioRxiv2017

Distinct roles of cohesin-SA1 and cohesin-SA2 in 3D chromosome organization

In addition to mediating sister chromatid cohesion, cohesin plays a central role in DNA looping and segmentation of the genome into contact domains (TADs). Two variant cohesin complexes that contain either STAG/SA1 or SA2 are present in all cell types. Here we addressed their specific contribution to genome architecture in non-transformed human cells. We found that cohesin-SA1 drives stacking of cohesin rings at CTCF-bound sites and thereby contributes to the stabilization and preservation of TAD boundaries. In contrast, a more dynamic cohesin-SA2 promotes cell type-specific contacts between enhancers and promoters within TADs independently of CTCF. SA2 loss, a condition frequently observed in cancer cells, results in increased intra-TAD interactions, likely altering the expression of key cell identity genes.

genomics↗