Biology subjects

Livera, G.

Publications and source records attributed to Livera, G..

7 recordsLinked to original sources

bioRxiv2024

Genome-wide transcriptional silencing and mRNA stabilization allow the coordinated expression of the meiotic program in mice

The transcriptional dynamic of mammalian cells when these transit from the ubiquitous mitotic to a meiotic specific program is key to understand this switch central to sexual reproduction. By quantifying active RNA polymerase II and nascent transcripts using single cell dataset and ethynyl-uridine pool-down with sorted cells from synchronised testes, we detailed the transcriptional activity of murine male germ cells. When spermatogonia differentiate, transcription slows down, reaching minimal activity at meiotic entry and resumes during pachytene stage. This event, we termed EMLT (for early meiotic low transcription), is distinct from the silencing of sex chromosomes as it is independent of Setdb1 though it is accompanied by the same chromatin mark, H3K9me3. EMLT is delayed in Stra8KO but occurs in mutants altering meiotic chromosome structure or DSB formation or repair. By comparing transcript abundance and neotranscription we unveil a massive event of mRNA stabilization that parallels EMLT. Altogether our data indicate that meiosis is initiated with a nearly silent genome and we propose that the stabilization of transcripts at that time facilitates the meiotic entry by synchronising the expression of several meiotic sub-programs.

cell biology↗

bioRxiv2023

Evidence of the ability of endocrine disrupting compounds to induce testicular germ cell cancer in humans.

Testicular cancer is an increasing burden in modern societies and the most common malignancy among young adult males. Environment contaminants, especially endocrine disrupting compounds (EDC), may play a significant role in the development of these cancers through epigenetic alterations occurring during fetal and neonatal development. As long-term studies in humans and suitable experimental models with the potential to develop testicular cancer are lacking, no causal link can be established between endocrine disruptor exposure and testicular cancer incidence. Therefore, we developed an experimental model that recapitulates the differentiation of germ cells from primordial germ cells (pluripotency) into spermatocytes (meiosis) by using xenografted human fetal testis combined with germ cell transplantation into adult testis compartments. Using this model, we demonstrate that long-term fetal exposure (until 12 weeks) to a mixture of Di-2-ethylhexylphthalate (DEHP) and Bisphenol A (BPA), two most prevalent plasticizers, could interfere with fetal germ cell differentiation, leading to carcinogenesis and seminomas. Transcriptome, methylome, and histological analyses reveal that BPA/DEHP exposure induced some significant hallmarks of germ cell tumors to occur: persistent pluripotent and proliferative germ cells, global hypomethylation of CpGs in germ cells, abnormal expression of meiotic markers and fibrotic signatures in fetal testis. Additionally, we found that EDC-exposed fetal germ cells were more likely to develop seminoma in a context that allows spermatogenesis to begin. This study proposes the first experimental evidence that EDC exposure can cause long-term, irreversible lesions in fetal germ cells, which then lead to testicular tumorigenesis in adults.

cancer biology↗

bioRxiv2022

In vivo inactivation of RAD51-mediated homologous recombination leads to premature aging, but not to tumorigenesis

Genetic instability is a hallmark of both cancer and aging. Homologous recombination (HR) is a prominent DNA repair pathway maintaining genomic integrity. Mutations in many HR genes lead to cancer predisposition. Paradoxically, the consequences of mutations in the pivotal HR player, RAD51, on cancer development remain puzzling. Moreover, in contrast with other HR genes, RAD51 mouse models are not available to experimentally address the role of RAD51 on aging and carcinogenesis, in vivo. Here, we engineered a mouse model with an inducible dominant negative form of RAD51 (SMRad51) that suppresses RAD51-mediated HR without stimulating alternative non-conservative repair pathways. We found that, in vivo expression of SMRad51 did not trigger tumorigenesis, but instead induced premature aging. We propose that these in vivo phenotypes result from the exhaustion of proliferating progenitors submitted to chronic endogenous replication stress resulting from RAD51-mediated HR suppression. Our data underline the importance of the RAD51 activity for progenitors homeostasis, preventing aging, and more generally for the balance between cancer and aging.

cancer biology↗

bioRxiv2020

DNA oxidation induced by fetal exposure to BPA agonists impairs female meiosis

Many endocrine disruptors have been proven to impair the meiotic process that is mandatory to produce healthy gametes. Bisphenol A is emblematic as it impairs meiotic prophase I and causes oocyte aneuploidy following in utero exposure. However, the mechanisms underlying these deleterious effects remain poorly understood. Furthermore, the increasing uses of BPA analogs raise concerns for public health. Here, we investigated the effect on oogenesis in mouse of fetal exposure to two BPA analogs, Bisphenol A Diglycidyl Ether (BADGE) or Bisphenol AF (BPAF). These analogs delay meiosis initiation, increase MLH1 foci per cell and induce oocyte aneuploidy. We further demonstrate that these defects are accompanied by a deregulation of gene expression and aberrant mRNA splicing in fetal premeiotic germ cells. Interestingly, we observed an increase in DNA oxidation after exposure to BPA analogs. Specific induction of oxidative DNA damages during fetal germ cell differentiation causes similar defects during oogenesis, as observed in 8-Oxoguanine DNA Glycosylase (OGG1) deficient mice or after in utero exposure to potassium bromate (KBrO3), an inducer of oxidative DNA damages. Moreover, the supplementation of N-acetylcysteine (NAC) with BPA analogs counteracts the bisphenol-induced meiotic effect. Together our results position oxidative stress as a central event that negatively impacts the female meiosis with major consequences on oocyte quality. This could be a common mechanism of action for so called endocrine disruptors pollutants and it could lead to novel strategies for reprotoxic compounds.

molecular biology↗

bioRxiv2020

shani mutation in mouse affects splicing of Spata22 and leads to impaired meiotic recombination

Recombination is crucial for chromosome pairing and segregation during meiosis. SPATA22, along with its direct binding partner and functional collaborator, MEIOB, is essential for the proper repair of double-strand breaks (DSBs) during meiotic recombination. Here we describe a novel point-mutated allele (shani) of mouse Spata22 that we isolated in a forward genetic screen. shani mutant mice phenocopy Spata22-null and Meiob-null mice: mutant cells appear to form DSBs and initiate meiotic recombination, but are unable to complete DSB repair, leading to meiotic prophase arrest, apoptosis and sterility. shani mutants show precocious loss of DMC1 foci and improper accumulation of BLM-positive recombination foci, reinforcing the requirement of SPATA22-MEIOB for the proper progression of meiotic recombination events. The shani mutation lies within a Spata22 coding exon and molecular characterization shows that it leads to incorrect splicing of the Spata22 mRNA, ultimately resulting in no detectable SPATA22 protein. We propose that the shani mutation alters an exonic splicing enhancer element (ESE) within the Spata22 transcript. The affected DNA nucleotide is conserved in most tetrapods examined, suggesting that the splicing regulation we describe here may be a conserved feature of Spata22 regulation.

genetics↗

bioRxiv2019

A homozygous hypomorphic BRCA2 variant causes primary ovarian insufficiency without cancer or Fanconi anemia traits.

Primary Ovarian insufficiency (POI) affects 1% of women under forty. We studied a patient with a non-syndromic POI, from a consanguineous Turkish family. Exome sequencing identified a homozygous missense variant c.8524C>T/p.R2842C in BRCA2. BRCA2 is a major player in homologous recombination (HR). BRCA2 deficiency induces cancer predisposition and Fanconi Anemia (FA). Remarkably, neither the patient nor her family exhibit somatic pathologies. The patients somatic cells presented intermediate levels of chromosomal breaks, cell proliferation and radiation-induced RAD51 foci formation when compared to controls, the heterozygous mothers and FA cells. R2842C-BRCA2 partially complemented BRCA2 depletion for double-strand break-induced HR. The residual HR function in patients cells could explain the absence of somatic pathology. BRCA2 is expressed in human fetal ovaries in pachytene stage oocytes, when meiotic HR occurs. This study has a major impact on the understanding of genome maintenance in somatic and meiotic cells and on the management of POI patients.

genetics↗

bioRxiv2018

MEIOB and SPATA22 resemble RPA subunits and interact with the RPA complex to promote meiotic recombination

Homologous recombination is a conserved DNA repair process mandatory for chromosome segregation during meiosis. RPA, a ubiquitous complex essential to recombination, is thought to play a similar role during mitotic and meiotic recombination. MEIOB, a meiosis-specific factor with unknown molecular function, ressembles a RPA subunit. Here we use in vivo approaches to show that in mouse spermatocytes, DMC1 and RAD51 appear to be normally loaded in the absence of MEIOB but are prematurely lost from unrepaired recombination sites. This loss correlates with an accumulation of the BLM helicase on meiotic chromosomes. We also show that MEIOB alters the immunodetection of RPA subunits at meiotic recombination sites. Using electron microscopy and purified proteins, we demonstrate that the MEIOB-SPATA22 complex associates with and modifies the conformation of RPA-coated ssDNA. Finally, we identify structural homology between MEIOB, SPATA22 and RPA subunits, and show that MEIOB and SPATA22 interact through C-terminal OB-fold containing domains (OBCDs) like RPA subunits. Moreover, MEIOB and SPATA22 cooperate to interact with RPA through their OBCDs. Our results suggest that MEIOB, SPATA22 and RPA work together to ensure proper processing of meiotic recombination intermediates.

cell biology↗