Biology subjects

Noyvert, B.

Publications and source records attributed to Noyvert, B..

4 recordsLinked to original sources

bioRxiv2021

GENETICALLY-DETERMINED MYB INSUFFICIENCY DIRECTLYIMPACTS ON PROTEOSTASIS IN HEMATOPOIETIC STEM CELLSPREDISPOSING TO AGE-RELATED MYELOID NEOPLASIA

The Myb transcription factor plays critical roles in normal and malignant hematopoiesis. Acquired genetic dysregulation of Myb, which plays a central role in hematopoietic stem cell (HSC) gene regulation, is involved in the etiology of a number of leukemias. Also, inherited non-coding variants of the Myb gene are a factor in susceptibility to many hematological conditions, including myeloproliferative neoplasms (MPN), but the mechanisms by which variations in Myb levels predispose to disease, including age-dependency in disease occurrence, are completely unknown. Here, we address these key points by showing that Myb insufficiency in mice leads in later life to MPN, myelodysplasia, and leukemia, mirroring the age profile of equivalent human diseases. This age-dependence is intrinsic to HSC, involving progressive accumulation of subtle changes. Interestingly, and linking to previous studies showing the importance of proteostasis to the maintenance of normal HSC, we observed altered proteosomal activity in young Myb-insufficient mice and later elevated ribosome activity. We propose that these alterations collectively cause an imbalance in proteostasis, potentially creating a cellular milieu favoring disease initiation by driver mutations.

cancer biology↗

bioRxiv2021

Gata2a maintains cebpa and npm1a in haematopoietic stem cells to sustain lineage differentiation and genome stability

The transcription factor Gata2 is required to produce and maintain haematopoietic stem and progenitor cells (HSPCs) in development and adult haematopoiesis. Mutations in GATA2 lead to GATA2 deficiency syndrome and predispose patients to acquire leukaemia. Here we use zebrafish gata2a enhancer deletion mutants and single cell transcriptomics to understand how GATA2 mediates survival and differentiation of haematopoietic stem cells in GATA2 deficiency. Gata2a mutants show marrow failure, neutropenia, B-lymphopenia and erythrocytosis from 6 months post-fertilization (mpf). Single cell transcriptional profiling of the adult kidney marrow demonstrated that HSPCs express elevated expression of erythroid- and decreased expression of myeloid genes, including cebpa. This is associated with a lineage skewing towards the erythroid fate at the expense of the myeloid fate. Thus, Gata2a is required to initiate and maintain lineage priming in HSPCs, favouring myeloid differentiation. Gata2a regulates expression of multiple targets associated with replication and DNA damage repair (DDR), including npm1a, a zebrafish NPM1 orthologue. Accordingly, mutant marrow cells show increased DNA damage associated with progressive loss of npm1a expression with age. This effect was replicated by inhibiting NPM1 activity in murine HPC7 progenitor cells. We propose that the impaired DDR leads to marrow failure in GATA2 deficiency. This leads to increased genomic instability in the surviving HSPCs, favouring acquisition of secondary leukaemogenic mutations.

cancer biology↗

bioRxiv2021

The chromatin insulator CTCF regulates HPV18 transcript splicing and differentiation-dependent late gene expression

The ubiquitous host protein, CCCTC-binding factor (CTCF), is an essential regulator of cellular transcription and functions to maintain epigenetic boundaries, stabilise chromatin loops and regulate splicing of alternative exons. We have previously demonstrated that CTCF binds to the E2 open reading frame (ORF) of human papillomavirus (HPV) 18 and functions to repress viral oncogene expression in undifferentiated keratinocytes by co-ordinating an epigenetically repressed chromatin loop within HPV episomes. Cellular differentiation, which is necessary for HPV life cycle completion disrupts CTCF-dependent chromatin looping of HPV18 episomes inducing enhanced activity of the HPV18 early promoter P105 and increased viral oncogene expression. To further characterise CTCF function in HPV transcription control we utilised direct, long-read Nanopore RNA-sequencing which provides information on the structure and abundance of full-length transcripts. Nanopore analysis of primary human keratinocytes containing HPV18 episomes before and after synchronous differentiation allowed quantification of viral transcript species in these cultures, including the identification of low abundance novel transcripts. Comparison of transcripts produced in wild type HPV18 genome-containing cells to those identified in CTCF-binding deficient genome-containing cells (HPV18-{Delta}CTCF) identifies CTCF as a key regulator of differentiation-dependent late promoter activation, required for efficient E1^E4 and L1 protein expression. Furthermore, our data show that CTCF binding at the E2 ORF of HPV18 promotes usage of the downstream weak splice donor (SD) sites SD3165 and SD3284, to the dominant E4 splice acceptor site at nucleotide 3434. These findings demonstrate importance of CTCF-dependent transcription regulation at multiple stages of the HPV life cycle. IMPORTANCEOncogenic human papillomavirus (HPV) infection is the cause of a subset of epithelial cancers of the uterine cervix, other anogenital areas and the oropharynx. HPV infection is established in the basal cells of epithelia where a restricted programme of viral gene expression is required for replication and maintenance of the viral episome. Completion of the HPV life cycle is dependent on the maturation (differentiation) of infected cells which induces enhanced viral gene expression and induction of capsid production. We previously reported that the host cell transcriptional regulator, CTCF, is hijacked by HPV to control viral gene expression. In this study, we use long-read mRNA sequencing to quantitatively map the variety and abundance of HPV transcripts produced in early and late stages of the HPV life cycle and to dissect the function of CTCF in controlling HPV gene expression and transcript processing.

microbiology↗

bioRxiv2021

Germline loss-of-function variants in the base-excision repair gene MBD4 cause a Mendelian recessive syndrome of adenomatous colorectal polyposis and acute myeloid leukaemia

Inherited defects in base-excision repair (BER) predispose to adenomatous polyposis and colorectal cancer (CRC), yet our understanding of this important DNA repair pathway remains incomplete. By combining detailed clinical, histological and molecular profiling, we reveal biallelic germline loss-of-function (LOF) variants in the BER gene MBD4 to predispose to adenomatous polyposis and -uniquely amongst CRC predisposition syndromes- to myeloid neoplasms. Neoplasms from MBD4-deficient patients almost exclusively accumulate somatic CpG>TpG mutations, resembling mutational signature SBS1. MBD4-deficient adenomas harbour mutations in known CRC driver genes, although AMER1 mutations were more common and KRAS mutations less frequent. We did not find an increased risk for colorectal tumours in individuals with a monoallelic MBD4 LOF variant. We suggest that this condition should be termed MBD4-associated neoplasia syndrome (MANS) and that MBD4 is included in testing for the genetic diagnosis of polyposis and/or early-onset AML.

genetics↗