Biology subjects

Koyunlar, C.

Publications and source records attributed to Koyunlar, C..

6 recordsLinked to original sources

bioRxiv2024

Hematological phenotypes in GATA2 deficiency syndrome arise from secondary injuries and maladaptation to proliferation

The GATA2 transcription factor is a pivotal regulator of hematopoiesis. Disruptions in the GATA2 gene drive severe hematologic abnormalities and are associated with an increased risk of myelodysplastic syndromes and acute myeloid leukemia; however, the mechanisms underlying the pathophysiology of GATA2 deficiency remain still unclear. We developed two different mouse models that are based on serial and limiting donor cell transplantation of (aged) GATA2 haploinsufficient cells and mirror the symptoms of GATA2 deficiency. Similar to what has been observed in patients, our models show that GATA2 haploinsufficiency leads to B lymphopenia, monocytopenia, lethal bone marrow failure (BMF), myelodysplasia and leukemia. Leukemia arises exclusively as a result of BMF, driven by somatic aberrations and accompanied by increased Myc target expression and genomic instability. These findings were confirmed in human GATA2+/- K562 cell lines showing defects in cytokinesis and are in line with the fact that monosomy 7 and trisomy 8 are frequent events in patients with MDS. Key pointsO_LIIn a mouse model for GATA2 deficiency, leukemia emerges from bone marrow failure C_LIO_LIMaladaptation to proliferative signals and chromosomal segregation defects contribute to the hematological phenotypes in GATA2 deficiency C_LI

cell biology↗

bioRxiv2022

Gata2-regulated Gfi1b expression controls endothelial programming during endothelial-to-hematopoietic transition

The first hematopoietic stem cells (HSCs) are formed through endothelial-to-hematopoietic transition (EHT) events during embryonic development. The transcription factor GATA2 is a crucial regulator of EHT and HSC function throughout life. Because GATA2 haploinsufficiency patients have inborn mutations, prenatal defects are likely to have an influence on disease development. In mice, Gata2 haploinsufficiency (Gata2+/-) reduces the number and the functionality of embryonic hematopoietic stem and progenitor cells (HSPCs) generated through EHT. However, the embryonic HSPC pool is heterogeneous and the mechanisms underlying this defect in Gata2+/- embryos are unclear. Here, we investigated whether Gata2 haploinsufficiency selectively affects a cellular subset undergoing EHT. We show that Gata2+/- HSPCs initiate but cannot fully activate hematopoietic programming during EHT. In addition, due to reduced activity of the endothelial repressor Gfi1b, Gata2+/- HSPCs cannot repress the endothelial identity to complete maturation. Finally, we show that hematopoietic-specific induction of gfi1b can restore HSC production in gata2b-null (gata2b-/-) zebrafish embryos. This study illustrates pivotal roles of Gata2 on the regulation of transcriptional network governing HSPC identity throughout EHT. HighlightsO_LIMaturation of embryonic Gata2+/- HSPCs is disturbed due to aberrant endothelial gene expression and incomplete activation of hematopoietic transcriptional programming. C_LIO_LIGata2 activates Gfi1b to repress endothelial identity of embryonic HSPCs during maturation. C_LIO_LIHematopoietic-specific induction of gfi1b restores the number of embryonic HSCs in gata2b-/- zebrafish. C_LI

developmental biology↗

bioRxiv2021

Gata2b haploinsufficiency causes aberrant transcriptional signatures in HSPCs resulting in myeloid and erythroid dysplasia in zebrafish

The transcription factor GATA2 has pivotal roles in hematopoiesis. Germline GATA2 mutations in patients result in GATA2 haploinsufficiency syndrome characterized by immunodeficiency, bone marrow failure, and predispositions to myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). Clinical symptoms in GATA2 patients are diverse and mechanisms driving GATA2 related phenotypes largely unknown. To explore the impact of GATA2 haploinsufficiency on hematopoiesis, we generated a zebrafish model carrying a heterozygous mutation of gata2b (gata2b+/-), an orthologue of GATA2. Morphological analysis revealed myeloid and erythroid dysplasia in gata2b+/- kidney marrow (KM). single nucleus (sn)-ATAC-seq showed that the co-accessibility between the transcription start site (TSS) and a +3.5-4.1kb enhancer was more robust in gata2b+/- zebrafish HSPCs compared to wild type, increasing gata2b expression. This is suggestive of an auto-regulatory feedback mechanism, where gata2b expression remains at sufficient levels after the loss of a single allele to maintain the HSPC pool. As a result, gata2b+/- chromatin is also more accessible in the erythroid and myeloid lineage, causing several defects. scRNA-seq data revealed a differentiation delay in erythroid progenitors, hallmarked by downregulation of intrinsic signals like cytoskeletal transcripts, aberrant proliferative signatures, and downregulation of Gata1a, a master regulator of erythropoiesis, likely preceding erythroid dysplasia. This shows that the cell intrinsic compensatory mechanisms for the maintenance of normal levels of Gata2b to maintain HSPC integrity result in aberrant lineage differentiation and a preleukemia syndrome.

cancer biology↗

bioRxiv2020

Knockout of zebrafish desmin genes does not cause skeletal muscle degeneration but alters calcium flux

Desmin is a muscle-specific intermediate filament protein that has fundamental role in muscle structure and force transmission. Whereas human desmin protein is encoded by a single gene, two desmin paralogs (desma and desmb) exist in zebrafish. Desma and desmb show differential spatiotemporal expression during zebrafish embryonic and larval development, being similarly expressed in skeletal muscle until hatching, after which expression of desmb shifts to gut smooth muscle. We generated knockout (KO) mutant lines carrying loss-of-function mutations for each gene by using CRISPR/Cas9. Mutants are viable and fertile, and lack obvious skeletal muscle, heart or intestinal defects. In contrast to morphants, knockout of each gene did not cause any overt muscular phenotype, but did alter calcium flux in myofibres. These results point to a possible compensation mechanism in these mutant lines generated by targeting nonsense mutations to the first coding exon.

developmental biology↗

bioRxiv2019

Single cell transcriptome analysis reveals an essential role for Gata2b in hematopoietic lineage decisions in zebrafish

Hematopoietic stem cells (HSCs) are tightly controlled to keep a balance between myeloid and lymphoid cell differentiation. Gata2 is a pivotal hematopoietic transcription factor required for HSC generation and maintenance. We generated a zebrafish mutant for the mammalian Gata2 orthologue, gata2b. We found that in adult zebrafish, gata2b is required for both neutrophilic- and monocytic lineage differentiation. Single cell transcriptome analysis revealed that the myeloid defect present in Gata2b deficient zebrafish arise in the most immature hematopoietic stem and progenitor cell (HSPC) compartment and that this population is instead committed towards the lymphoid and erythroid lineage. Taken together, we find that Gata2b is vital for the fate choice between the myeloid and lymphoid lineages.

immunology↗

bioRxiv2019

A zebrafish model for MonoMAC syndrome identifies an earlier role for gata2 in haemogenic endothelium programming and generation of haematopoietic stem cells

Haematopoietic stem and progenitor cells (HSPCs) maintain the vertebrate blood system throughout life and their emergence from haemogenic endothelium (HE) is regulated by transcription factors such as Gata2. Here we deleted a conserved enhancer (i4 enhancer) driving pan-endothelial expression of gata2a and showed that Gata2a is required for HE programming by regulating expression of runx1 and of the second zebrafish Gata2 orthologue, gata2b. By 5 days, homozygous gata2a{Delta}i4/{Delta}i4 larvae showed normal numbers of HSPCs, a recovery mediated by Notch signalling driving gata2b and runx1 expression in HE. However, gata2a{Delta}i4/{Delta}i4 adults showed oedema, susceptibility to infections and marrow hypo-cellularity, consistent with bone marrow failure found in GATA2 deficiency syndromes. Thus, gata2a expression driven by the i4 enhancer is required for HE programming in embryos and maintenance of steady-state haematopoietic stem cell output in the adult. These enhancer mutants are a new paradigm to explore the pathophysiology of GATA2-related deficiencies in vivo.

developmental biology↗