Biology subjects

Levin-Klein, R.

Publications and source records attributed to Levin-Klein, R..

6 recordsLinked to original sources

bioRxiv2026

CTCF-mediated cis-regulatory chromatin insulation enforces a central B-cell tolerance checkpoint

The generation of a diverse and self-tolerant B cell repertoire is essential for adaptive immunity and is achieved through V(D)J recombination. In mice, Ig{kappa} is the dominant light chain, whereas Ig{lambda} rearrangement typically occurs in response to nonproductive or autoreactive Ig{kappa} recombination, a process termed receptor editing. Recombination at the RS element deletes the Ig{kappa} constant exon, silencing the locus and enabling Ig{lambda} expression. However, the epigenetic regulatory framework that orchestrates and governs receptor editing remains poorly defined. Here, we identify a CTCF-binding insulator element (CBE) within the 3' Ig{kappa} super-enhancer (3'-SE{kappa}) that regulates receptor editing and directs the {kappa}-to-{lambda} switch required for Ig{lambda} B-cell development. Mechanistically, loss of this CBE activates an insulated enhancer within the 3'-SE{kappa}, causing aberrant V{kappa} rearrangements and altered chromatin interactions through disrupted loop extrusion dynamics. Notably, loss of this CBE in mice leads to increased autoantibody production by ten weeks of age, demonstrating that CBE-mediated chromatin architecture shapes B cell fate by constraining autoreactive potential. Collectively, our findings define a novel CTCF-dependent cis-regulatory insulation checkpoint that connects chromatin loop extrusion to antigen-driven receptor editing, thereby enforcing B-cell tolerance.

immunology↗

bioRxiv2025

Single-Cell Spatial Mapping of Human Kidney Development Reveals the Critical Role of the Local Microenvironment in Cell Fate Decisions

Cell-cell interactions play a pivotal role in organ development, yet these communications have previously been studied one interaction at a time in model organisms, leaving a gap in our understanding of the cellular interplay in human development. To address this, we investigated human kidney development using single-cell RNA sequencing and spatial transcriptomics, analyzing over 500,000 cells. By mapping gene expression and differentiation trajectories in histologic space, we define the spatial organization of kidney development. Our analysis revealed newfound plasticity, showing that nephron progenitor cells undergo an early fate decision between renal corpuscle and tubular lineages. However, this choice is later reversed with some mature tubule cells transitioning back to a renal corpuscle fate. Further, through a genome-wide, spatially-aware cell-cell interaction analysis, we identified specific ligands and neighboring cell signals that create biologically meaningful cellular neighborhoods and mediate cell fate choices, offering a blueprint to understand the coordination of human development at scale.

genomics↗

bioRxiv2023

Amniotic Fluid Organoids As Personalized Tools For Real-Time Modeling Of The Developing Fetus

Despite biomedical advances, major knowledge gaps regarding human development remain, and many developmental disorders lack effective treatment, representing a huge clinical burden. This results from fetuses being largely inaccessible for analysis. Here, we employ fetal cells in human amniotic fluid (AF) to establish personalized fetal kidney and lung organoids (AFKO and AFLO, respectively), recapitulating fetal organs at single-cell resolution. AFKO harbor key fetal kidney cell populations, including nephrogenic, urothelial and stromal, endocytose albumin, and model PAX2-related anomalies. Strikingly, upon injection into the nephrogenic cortex of human fetal kidney explants, AFKO-derived progenitors integrate into the host progenitor niche and contribute to developing nephrons. AFLO comprise alveolar cells and most airway cell types in a typical pseudostratified structure, upregulate surfactant expression upon corticosteroid treatment, and show functional CFTR channels. Overall, this platform represents a new personalized tool that can be applied to virtually any fetus in real-time, affording unprecedented options in studying development, uncovering mechanisms of in utero pathologies (e.g., congenital anomalies, infections or chemical teratogens) deciphering the developmental origins of chronic diseases, and tailoring treatments for these pathologies, as well as for prematurity-related complications. Importantly, since AF contains cells from additional tissues (e.g., skin and gastrointestinal tract), and is derived in a procedure already performed in many patients, this platform may well become a broadly applicable tool in fetal medicine.

developmental biology↗

bioRxiv2023

Human APOBEC3B promotes tumor heterogeneity in vivo including signature mutations and metastases

The antiviral DNA cytosine deaminase APOBEC3B has been implicated as a source of mutation in many different cancers. Despite over 10 years of work, a causal relationship has yet to be established between APOBEC3B and any stage of carcinogenesis. Here we report a murine model that expresses tumor-like levels of human APOBEC3B after Cre-mediated recombination. Animals appear to develop normally with full-body expression of APOBEC3B. However, adult males manifest infertility and older animals of both sexes show accelerated rates of tumorigenesis (mostly lymphomas or hepatocellular carcinomas). Interestingly, primary tumors also show overt heterogeneity, and a subset spreads to secondary sites. Both primary and metastatic tumors exhibit increased frequencies of C-to-T mutations in TC dinucleotide motifs consistent with the established biochemical activity of APOBEC3B. Elevated levels of structural variation and insertion-deletion mutations also accumulate in these tumors. Together, these studies provide the first cause-and-effect demonstration that human APOBEC3B is an oncoprotein capable of causing a wide range of genetic changes and driving tumor formation in vivo.

cancer biology↗

bioRxiv2019

APOBEC3A Catalyzes Mutation and Drives Carcinogenesis In Vivo

The APOBEC3 family of antiviral DNA cytosine deaminases is implicated as the second largest source of mutation in cancer. This mutational process may be a causal driver or inconsequential passenger to the overall tumor phenotype. We show that human APOBEC3A expression in murine colon and liver tissues increases tumorigenesis. All other APOBEC3 family members including APOBEC3B did not as strongly promote liver tumor formation. DNA sequences from APOBEC3A-expressing animals display hallmark APOBEC signature mutations in TCA/T motifs. Bioinformatic comparisons of the observed APOBEC3A mutation signature in murine tumors, previously reported APOBEC3A and APOBEC3B mutation signatures in yeast, and reanalyzed APOBEC mutation signatures in human tumor data sets support cause-and-effect relationships for APOBEC3A-catalyzed deamination and mutagenesis in driving multiple human cancers.

cancer biology↗

bioRxiv2019

A rabbit monoclonal antibody against the antiviral and cancer genomic DNA mutating enzyme APOBEC3B

The DNA cytosine deaminase APOBEC3B (A3B) is normally an antiviral factor in the innate immune response. However, A3B has been implicated in cancer mutagenesis, particularly in solid tumors of the bladder, breast, cervix, head/neck, and lung. Here, we report data on the generation and characterization of a rabbit monoclonal antibody (mAb) for human A3B through a series of immunoblot, immunofluorescence microscopy, and immunohistochemistry experiments. Positive results indicate that one mAb, 5210-87-13, will be useful for fundamental research in virology and cancer biology and that immunohistochemical quantification of A3B enzyme levels may constitute a clinical biomarker for tumor evolvability and differential treatment.

cancer biology↗