Biology subjects

Bombelli, S.

Publications and source records attributed to Bombelli, S..

3 recordsLinked to original sources

bioRxiv2025

Competing gene regulatory networks drive naive and memory B cell differentiation

Elucidating the gene regulatory networks (GRNs) that govern human B cell differentiation is essential for understanding immune responses to infection, vaccination and autoantigens. Here, we show that individual naive B cells can give rise to both plasma cells and germinal centre (GC) B cells. In contrast, memory B cells display a progressive increase in IRF4 activity over time, leading to PRDM1 induction and exclusive differentiation into plasma cells. Using CRISPR-based perturbations, we demonstrate that IRF4 is indispensable for both GC and plasma cell development. Notably, IRF4 promotes GC fate independently of PRDM1, as PRDM1 disruption did not impair GC differentiation. We also find that while the abundance of antibody mRNAs is clonally correlated, class switch recombination (CSR) occurs stochastically and is clonally independent. Together, these findings reveal distinct regulatory dynamics during naive and memory B cell activation and offer new insights into the GRNs underlying human B cell fate decisions.

immunology↗

bioRxiv2024

Hemogenic endothelium of the vitelline and umbilical arteries is the major contributor to mouse fetal lympho-myelopoiesis

Embryonic hematopoiesis consists of distinct waves originating in rapid succession from different anatomical locations. Hematopoietic progenitors appearing earlier than definitive hematopoietic stem cells (HSCs) play key roles in fetal and postnatal life. However, their precise origin, identity and the extent of their contribution need further clarification. To this aim, we took advantage of a genetic fate-mapping strategy in mice that allows labeling and tracking of distinct subsets of hemogenic endothelium (HE). Time-course labeling of hematopoietic progenitors emerging from HE between E8.5 and E9.5, before intra-embryonic definitive HSC generation, revealed a major fetal lympho-myeloid contribution which declined in the adult. Lineage tracing coupled with whole-mount imaging and single-cell RNA sequencing located its source within hematopoietic clusters of vitelline and umbilical arteries. Functional assays confirmed the transient nature of these progenitors. We therefore unveiled a hitherto unidentified early wave of fetal-restricted hematopoietic stem/progenitor cells poised for differentiation that provide a major contribution to pre-natal hematopoiesis.

developmental biology↗

bioRxiv2020

NOT ALL ANTIBODIES HAVE BEEN CREATED EQUAL: Antibodies validated for routinely processed tissue seldom apply to frozen tissue sections.

ABSTRACTA customized context-dependent validation of antibodies for the prospective use, rather than a general stamp of validity, is required for reproducibility and data validity, besides the need of standardized reagents. In-situ antibody staining is a technique broadly used in experimental settings and human diagnostic practice. The first typically, but not exclusively uses lightly fixed material (cell smears, frozen sections), the second, routinely processed formalin-fixed, paraffin-embedded (FFPE) tissue. Differently from techniques based on tissue extraction, there is little awareness of the context-dependent constraints inherent with either type of in situ staining except that antigen masking associated with routine tissue processing limits the range of useful antibodies. We applied a panel of 126 antibodies validated for FFPE to lightly fixed (acetone, formalin) frozen sections and found that less than 30% performed conservatively with all fixations, 35% preferred one fixation over another, 13% gave non-specific staining, 23% did not stain at all. Individual antibody variegation of the paratope fitness for the differentially fixed antigen may be the cause. Re-validation of established antibody panels is required when applied to sections whose fixation and processing is different from the tissue where they have been initially validated.Competing Interest StatementThe authors have declared no competing interest.View Full Text

pathology↗