Biology subjects

Valsoni, S.

Publications and source records attributed to Valsoni, S..

4 recordsLinked to original sources

bioRxiv2023

CD32 allows capturing blood cells emergence in slow motion during human embryonic development

During development, in the embryo proper blood cells emerge from a subset of specialized endothelial cells, named hemogenic endothelial cells (HECs), via a process known as endothelial-to-hematopoietic transition (EHT) driven by time-specific Notch signaling activation1. HECs represent an elusive cell population as they are rare and transient, rapidly generating blood cells, and specific markers are lacking. Therefore, it remains unclear how and when the hematopoietic fate is specified and how blood cell emergence is molecularly regulated. Notably, thorough characterization of this process is essential to guide the generation of therapeutic blood products in vitro from human pluripotent stem cells (hPSCs). To identify specific human HEC markers, we performed transcriptomic analysis of 28-32-day human embryos, a developmental stage characterized by active hematopoiesis. We observed that the expression of FCGR2B, encoding for the Fc receptor CD32, is highly enriched in the ACE+CD34+ endothelial cell population that contains HECs. Functional ex vivo analyses confirmed that multilineage hematopoietic potential is highly enriched in CD32+ endothelial cells isolated from human embryos. In addition, clonal analysis revealed that 90% of CD32+ hPSC-derived endothelial cells are bona fide HECs. We leveraged this specificity to study how HECs commit to the blood fate. Remarkably, our analyses indicated that HECs progress through different states culminating with the one identified by CD32 expression. Indeed CD32+ HECs no longer require Notch to generate hematopoietic progeny and display full commitment to hematopoiesis even before the expression of hematopoietic markers. These findings provide a precise method for isolating HECs primed to the blood fate from human embryos and hPSC cultures, thus allowing the efficient generation of hematopoietic cells in vitro.

developmental biology↗

bioRxiv2022

In vitro selection of Engineered Transcriptional Repressors for targeted epigenetic silencing and initial evaluation of their specificity profile

Gene inactivation is instrumental to study gene function and represents a promising strategy for the treatment of a broad range of diseases. Among traditional technologies, RNA interference suffers from partial target abrogation and requirement for life-long treatments. On the other hand, artificial nucleases can impose stable gene inactivation through induction of DNA Double Strand Breaks, but recent studies are questioning the safety of this approach. Targeted epigenetic editing via Engineered Transcriptional Repressors (ETRs) may represent a solution, as a single administration of specific ETRs combinations can lead to durable silencing without DNA breaks induction. ETRs are proteins containing a programmable DNA Binding Domain (DBD) and effectors from naturally occurring transcriptional repressors. Specifically, a combination of three ETRs equipped with the KRAB domain of human ZNF10, the catalytic domain of human DNMT3A and human DNMT3Lwas shown to induce heritable repressive epigenetic states on the ETR-target gene. The hit-and-run nature of this platform, the lack of impact on the DNA sequence of the target, and the possibility to revert on-demand the repressive state by DNA demethylation, make epigenetic silencing a game-changing tool. A critical step is the identification of the proper position on the target gene where to tether the ETRs in order to maximize on target and minimizing off-target silencing. Performing this step in the final ex vivo or in vivo preclinical setting can be cumbersome. Taking CRISPR-Cas9 system as a paradigmatic DBD for ETRs, here we describe a protocol consisting in the in vitro screen of gRNAs coupled to the triple ETRs combination for efficient on-target silencing, followed by evaluation of the genome-wide specificity profile of top hits. This allows to reduce the initial repertoire of candidate gRNAs to a short list of promising ones, whose complexity is suitable for their final evaluation in the therapeutically relevant setting of interest.

synthetic biology↗

bioRxiv2020

A ChIC solution for ChIP-seq quality assessment

Despite the widespread adoption of the ChIP-seq technique, there is still no consensus on quality assessment procedures. Quantitative metrics previously proposed in literature are not always effective in discriminating the success or failure of an experiment, thus hampering objectivity and reproducibility of quality control. Here we introduce ChIC, a new framework for ChIP-seq data quality assessment that overcomes the limitations of previous solutions. ChIC is the first method for ChIP-seq quality control directly considering the enrichment profile shape, thus achieving good performances on ChIP targets yielding sharp and broad peaks alike. We integrate a comprehensive set of quality control metrics into one single score reliably summarizing the sample quality. The ChIC score is based on a machine learning classifier trained on a compendium with thousands of ChIP-seq profiles, which can also be used as a reference for easier evaluation of new datasets. ChIC is implemented as a user-friendly R/Bioconductor package.

bioinformatics↗

bioRxiv2019

Early Polycomb-target deregulations in Hutchinson-Gilford Progeria Syndrome revealed by heterochromatin analysis

Hutchinson-Gilford progeria syndrome (HGPS) is characterized by the progressive accumulation of progerin, an aberrant form of Lamin A. This leads to chromatin structure disruption, in particular by interfering with Lamina Associated Domains. Although several cellular and molecular alterations have been characterized, it is still unclear how chromatin structural changes translate into premature senescence in HGPS. Moreover, early events in chromatin remodeling have not been detected so far. We developed a new high-throughput sequencing-based method, named SAMMY-seq, for genome-wide characterization of heterochromatin accessibility changes. Using SAMMY-seq, we detected early stage alterations of chromatin structure in HGPS primary fibroblasts. Of note, these structural changes do not disrupt the distribution of H3K9me3 but are associated with site-specific H3K27me3 variations and transcriptional dysregulation of Polycomb target genes. Our results show that SAMMY-seq represents a novel and sensitive tool to characterize heterochromatin alterations. Moreover, we found that the assembly of lamin associated domains is strictly connected to the correct Polycomb repression, rapidly lost in early HGPS pathogenesis.

molecular biology↗