Biology subjects

Djeghloul, D.

Publications and source records attributed to Djeghloul, D..

4 recordsLinked to original sources

bioRxiv2026

Non-Canonical Heme Oxygenase-1 Function in Hematopoietic Stem Cell Homeostasis and Aging

Heme oxygenase-1 (HO-1, encoded by Hmox1) is a cytoprotective enzyme with well-established roles in defending against oxidative stress. Global Hmox1 deficiency in mice accelerates hematopoietic stem cell (HSC) exhaustion and aging, effects previously attributed primarily to loss of HO-1 activity within the bone marrow (BM) niche. However, the cell-intrinsic contribution of HO-1 to HSC regulation has remained unclear. Here, we show that global Hmox1 deficiency results in accumulation of an expanded but largely quiescent HSC pool characterized by compromised genome maintenance, altered apoptotic signaling, and defective cell-cycle checkpoint control. We further demonstrate that HO-1 protein is expressed in HSCs and exhibits a predominantly nuclear, non-canonical localization. Using Hoxb5-CreERT2-mediated conditional deletion of Hmox1 in HSCs, we uncover an intrinsic requirement for HO-1 in controlling early hematopoietic differentiation. HSC-specific loss of HO-1 skews stem cell output toward short-term progenitors and increases colony-forming capacity. Transcriptomic profiling of Hmox1fl/fl;Hoxb5-CreERT2 HSCs revealed broad dysregulation of pathways involved in translation and RNA metabolism, together with aberrant expression of key transcription factors controlling hematopoietic differentiation. Collectively, these findings identify a non-canonical, cell-intrinsic role for HO-1 in regulating HSC homeostasis, differentiation, and aging.

cell biology↗

bioRxiv2024

PBK/TOPK mediates Ikaros, Aiolos and CTCF displacement from mitotic chromosomes and alters chromatin accessibility at selected C2H2-zinc finger protein binding sites

PBK/TOPK is a mitotic kinase implicated in haematological and non-haematological cancers. Here we show that the key haemopoietic regulators Ikaros and Aiolos require PBK-mediated phosphorylation to dissociate from chromosomes in mitosis. Eviction of Ikaros is rapidly reversed by addition of the PBK-inhibitor OTS514, revealing dynamic regulation by kinase and phosphatase activities. To identify more PBK targets, we analysed loss of mitotic phosphorylation events in Pbk-/-preB cells and performed proteomic comparisons on isolated mitotic chromosomes. Among a large pool of C2H2-zinc finger targets, PBK is essential for evicting the CCCTC-binding protein CTCF and zinc finger proteins encoded by Ikzf1, Ikzf3, Znf131 and Zbtb11. PBK-deficient cells were able to divide but showed altered chromatin accessibility and nucleosome positioning consistent with CTCF retention. Our studies reveal that PBK controls the dissociation of selected factors from condensing mitotic chromosomes and contributes to their compaction.

molecular biology↗

bioRxiv2022

Loss of H3K9 tri-methylation alters chromosome compaction and transcription factor retention during mitosis

Recent studies have shown that repressive chromatin machinery, including DNA methyltransferases (DNMTs) and Polycomb Repressor Complexes (PRCs), bind to chromosomes throughout mitosis and their depletion results in increased chromosome size. Here we show that enzymes that catalyse H3K9 methylation, such as Suv39h1, Suv39h2, G9a and Glp, are also retained on mitotic chromosomes. Surprisingly however, mutants lacking H3K9me3 have unusually small and compact mitotic chromosomes that are associated with increased H3S10ph and H3K27me3 levels. Chromosome size and centromere compaction in these mutants were rescued by providing exogenous Suv39h1, or inhibiting Ezh2 activity. Quantitative proteomic comparisons of native mitotic chromosomes isolated from wildtype versus Suv39h1/Suv39h2 double-null ESCs revealed that H3K9me3 was essential for the efficient retention of bookmarking factors such as Esrrb. These results highlight an unexpected role for repressive heterochromatin domains in preserving transcription factor binding through mitosis, and underscore the importance of H3K9me3 for sustaining chromosome architecture and epigenetic memory during cell division.

molecular biology↗

bioRxiv2019

Systematic identification of factors bound to isolated metaphase ESC chromosomes reveals a role for chromatin repressors in compaction

Epigenetic information is transmitted from mother to daughter cells through mitosis. To identify trans-acting factors and cis-acting elements that might be important for conveying epigenetic memory through cell division, we isolated native (unfixed) chromosomes from metaphase-arrested cells using flow cytometry and performed LC-MS/MS to determine the repertoire of chromosome-bound proteins. Quantitative proteomic comparisons between metaphase-arrested cell lysates and chromosome-sorted samples revealed a cohort of proteins that were significantly enriched on mitotic ESC chromosomes. These include pluripotency-associated transcription factors, repressive chromatin-modifiers (such as PRC2 and DNA methyl-transferases) and proteins governing chromosome architecture. We showed that deletion of PRC2, DNMT1/3a/3b or Mecp2 provoked an increase in the size of individual mitotic chromosomes consistent with de-condensation, as did experimental cleavage of cohesin complexes. These data provide a comprehensive inventory of chromosome-bound factors in pluripotent stem cells at mitosis and reveal an unexpected role for chromatin repressor complexes in preserving mitotic chromosome compaction.

cell biology↗