Biology subjects

Lazar, E.

Publications and source records attributed to Lazar, E..

7 recordsLinked to original sources

bioRxiv2026

In utero barcoding of mouse mesoderm reveals the clonal architecture of organ mesenchyme

The mesoderm coordinates organogenesis and generates the cardiovascular, visceral and musculoskeletal systems, yet in mammals this germ layer is difficult to access, impeding its genetic manipulation and study. Here, we establish embryonic day (E) 7.5 exocoelomic cavity nano-injection as a scalable route for selective genetic targeting of mouse mesoderm. Combining in utero lentiviral barcoding with single-cell and spatial transcriptomics, we reconstructed mesodermal and neural crest clonal relationships across >590,000 cells and 31,000 multicellular clones from E9.5-E10.5 embryos and E16.5 livers and hearts. In liver, capsular mesothelium was closely related to hepatic stellate cells, whereas fibroblast and vascular smooth muscle lineages diverged earlier. In heart, epicardium was clonally coupled to three spatially restricted mesenchymal sub-lineages but not to cardiomyocytes, and lineage tracing separated epicardial- and neural crest-derived populations within transcriptionally convergent valve mesenchyme. This approach enables Cre-independent manipulation of mammalian mesoderm and resolves organ mesenchyme development at clonal resolution.

developmental biology↗

bioRxiv2026

Dissecting human fetal cardiac repair using cardioids

Human cardiac injury responses are governed by dynamic interacting processes that are difficult to resolve. Unlike adults, fetal mammalian hearts regenerate through coordinated remodeling and proliferation supported by a pro-regenerative immune environment, extracellular matrix (ECM), and immature cardiomyocytes, including trabecular subtypes. Here, we establish a modular human cardioid injury platform to dissect these interactions. We show that anti-inflammatory macrophages selectively migrate to the injury, clear debris, and promote ECM remodeling, whereas inflammatory macrophages suppress cardiomyocyte proliferation. Synergistic FGF2-NRG1 signaling induces trabecular identity and morphology in a hyaluronan-dependent manner, conferring enhanced injury repair, characterized by cytoskeletal remodeling and cardiomyocyte proliferation mediated by YAP and WNT signaling. Exogenous YAP, but not WNT, is sufficient to promote repair in non-trabecular cardioids. These findings uncover coordinated immune-ECM-cardiomyocyte interactions governing human fetal regenerative competence and mechanistically resolve remodeling and proliferative components of cardiac repair. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=162 SRC="FIGDIR/small/735236v1_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@1e647a2org.highwire.dtl.DTLVardef@16911f8org.highwire.dtl.DTLVardef@11ad14eorg.highwire.dtl.DTLVardef@1a35d94_HPS_FORMAT_FIGEXP M_FIG C_FIG

developmental biology↗

bioRxiv2024

Spatial Dynamics of the Developing Human Heart

Heart development relies on a topologically defined interplay between a diverse array of cardiac cells. We finely curated spatial and single-cell measurements with subcellular imaging-based transcriptomics validation to explore spatial dynamics during early human cardiogenesis. Analyzing almost 80,000 individual cells and 70,000 spatially barcoded tissue regions between the 5.5th and 14th postconceptional weeks, we identified 31 coarse- and 72 fine-grained cell states and mapped them to highly resolved cardiac cellular niches. We provide novel insight into the development of the cardiac pacemaker-conduction system, heart valves, and atrial septum, and decipher heterogeneity of the hitherto elusive cardiac fibroblast population. Furthermore, we describe the formation of cardiac autonomic innervation and present the first spatial account of chromaffin cells in the fetal human heart. We support independent exploration of our datasets by an open-access, spatially centric interactive viewer. In summary, our study delineates the cellular and molecular landscape of the developing hearts architecture, offering links to genetic causes of heart disease.

developmental biology↗

bioRxiv2023

A latent cardiomyocyte regeneration potential in the human heart

Cardiomyocytes in the adult human heart show a regenerative capacity, with an annual renewal rate around 0.5%. Whether this regenerative capacity of human cardiomyocytes is employed in heart failure has been controversial. Using retrospective 14C birth dating we analyzed cardiomyocyte renewal in patients with end-stage heart failure. We show that cardiomyocyte generation is minimal in end-stage heart failure patients at rates 18-50 times lower compared to the healthy heart. However, patients receiving left ventricle support device therapy, who showed significant functional and structural cardiac improvement, had a >6-fold increase in cardiomyocyte renewal relative to the healthy heart. Our findings reveal a substantial cardiomyocyte regeneration potential in human heart disease, which could be exploited therapeutically.

cell biology↗

bioRxiv2022

FiNuTyper: an automated deep learning-based platform for simultaneous fiber and nucleus type analysis in human skeletal muscle

SummaryWhile manual quantification is still considered the gold standard for skeletal muscle histological analysis, it is time-consuming and prone to investigator bias. We assembled an automated image analysis pipeline, FiNuTyper (Fiber and Nucleus Typer), from recently developed deep learning-based image segmentation methods, optimized for unbiased evaluation of fresh and postmortem human skeletal muscle. We validated and utilized SERCA1 and SERCA2 as type-specific myonucleus and myofiber markers. Parameters including myonuclei per fiber, myonuclear domain, central myonuclei per fiber, and grouped myofiber ratio were determined in a fiber type-specific manner, revealing a large degree of gender- and muscle-related heterogeneity. Our platform was also tested on pathological muscle tissue (ALS) and adapted for the detection of other resident cell types (leukocytes, satellite cells, capillary endothelium). In summary, we present an automated image analysis tool for the simultaneous quantification of myofiber and myonuclear types, to characterize the composition of healthy and diseased human skeletal muscle. HighlightsO_LIA deep learning-based automated platform for skeletal muscle microscopic analysis C_LIO_LIHigh-fidelity identification and characterization of myonuclei and myofibers C_LIO_LIValidation of SERCA1 and SERCA2 as markers for myofiber and myonuclear subtypes C_LIO_LICharacterization of healthy and pathological human skeletal muscle tissue features C_LIO_LIAdaptations provided for studies on other resident cell types like satellite cells C_LI eTOC BlurbAn automated platform for unbiased analysis of skeletal muscle immunohistochemical images, focusing on type-specific myofiber-myonucleus relationships, facilitating high-throughput studies of healthy and diseased tissues.

cell biology↗

bioRxiv2022

Dual spatially resolved transcriptomics for SARS-CoV-2 host-pathogen colocalization studies in humans

To advance our understanding of cellular host-pathogen interactions, technologies that facilitate the co-capture of both host and pathogen spatial transcriptome information are needed. Here, we present an approach to simultaneously capture host and pathogen spatial gene expression information from the same formalin-fixed paraffin embedded (FFPE) tissue section using the spatial transcriptomics technology. We applied the method to COVID-19 patient lung samples and enabled the dual detection of human and SARS-CoV-2 transcriptomes at 55 m resolution. We validated our spatial detection of SARS-CoV-2 and identified an average specificity of 94.92% in comparison to RNAScope and 82.20% in comparison to in situ sequencing (ISS). COVID-19 tissues showed an upregulation of host immune response, such as increased expression of inflammatory cytokines, lymphocyte and fibroblast markers. Our colocalization analysis revealed that SARS-CoV-2+ spots presented shifts in host RNA metabolism, autophagy, NF{kappa}B, and interferon response pathways. Future applications of our approach will enable new insights into host response to pathogen infection through the simultaneous, unbiased detection of two transcriptomes.

genomics↗

bioRxiv2021

Identification and characterization of distinct cell cycle stages in cardiomyocytes using the FUCCI transgenic system

Understanding the regulatory mechanism by which cardiomyocyte proliferation transitions to endoreplication and cell cycle arrest during the neonatal period is crucial for identifying proproliferative factors and developing regenerative therapies. We used a transgenic mouse model based on the fluorescent ubiquitination-based cell cycle indicator (FUCCI) system to isolate and characterize cycling cardiomyocytes at different cell cycle stages at a single-cell resolution. Single-cell transcriptome analysis of cycling and noncycling cardiomyocytes was performed at postnatal days 0 (P0) and 7 (P7). The FUCCI system proved to be efficient for the identification of cycling cardiomyocytes with the highest mitotic activity at birth, followed by a gradual decline in the number of cycling and mitotic cardiomyocytes during the neonatal period. Cardiomyocytes showed premature cell cycle exit at G1/S shortly after birth and delayed G1/S progression during endoreplication at P7. Single-cell RNA-seq confirmed previously described signaling pathways involved in cardiomyocyte proliferation (Erbb2 and Hippo/YAP), cardiomyocyte motility, and maturation-related transcriptional changes during postnatal development, including the metabolic switch from glycolysis to fatty acid oxidation in cardiomyocytes. Additionally, we generated transcriptional profiles specific to cell division and endoreplication in cardiomyocytes. Deciphering transcriptional changes at different developmental stages and in a cell cycle-specific manner may facilitate the identification of genes important for adult cardiomyocyte proliferation and heart regeneration. Main findingsFUCCI reliably identifies cycling cardiomyocytes at distinct cell cycle stages in neonatal, juvenile, and adult hearts. Cell cycle activity decreases as the metabolic switch transitions from glycolysis to fatty acid metabolism in postnatal cardiomyocytes. Cell cycle arrest at G1/S is linked to the DNA damage response in postnatal cardiomyocytes. Distinct gene expression patterns are linked to different cell cycle phases in dividing and endoreplicating postnatal cardiomyocytes.

cell biology↗