Selich, A. | bioRxiv Science

bioRxiv2025

Septin7 is essential in early hematopoiesis, but redundant at later stages

The unique cytoskeletal protein Septin7 is generally considered to be required for cytokinesis in yeast and mammals. Whole body genetic ablation of Septin7 in mice is embryonic lethal. Septin7-deficient fibroblasts and HeLa cells are defective in cytokinesis and undergo obligate multinucleation. Surprisingly, lymphocyte- and myeloid-specific deletion of Septin7 in mice did not result in any detectable abnormalities in blood lineage development, suggesting that Septin7 is dispensable for steady-state hematopoiesis. In contrast, Septin7-deficient hematopoietic stem cells failed to engraft and establish donor chimerism following transplantation, indicating that Septin7 is essential for hematopoietic stem cell function under stress conditions. To reconcile these contradictory findings, we analyzed the effects of Septin7 deletion in hematopoietic cells from mice with either pan-hematopoietic or lymphoid lineage-specific Septin7 deletion. Our results demonstrate that Cre-induced deletion of the floxed Septin7 allele is inefficient during the early stages of hematopoiesis, suggesting strong selection pressure against Septin7 deficiency at this stage. In contrast, deletion of Septin7 at the common lymphoid progenitor stage, as well as in Hoxb8-immortalized hematopoietic progenitors, is efficient and does not result in any noticeable defects in cell division. Taken together, our findings indicate that Septin7 is essential during early hematopoiesis but becomes dispensable at later stages.

biochemistry↗

bioRxiv2018

DNA methylation patterns of replicative senescence are strand-specific and reflect changes in chromatin conformation

Culture expansion of primary cells evokes highly reproducible DNA methylation (DNAm) changes at specific sites in the genome. These changes might be due to an directly regulated epigenetic process, or to gradual deregulation of the epigenetic state, which is often referred to as "epigenetic drift". We have identified CG dinucleotides (CpGs) that become continuously hyper- or hypomethylated in the course of culture expansion of mesenchymal stem cells (MSCs) and other cell types. During reprogramming into induced pluripotent stem cells (iPSCs) particularly the culture-associated hypomethylation is reversed simultaneously with age-associated and pluripotency-associated DNAm changes. Bisulfite barcoded amplicon sequencing (BBA-seq) demonstrated that upon passaging the DNAm patterns of neighboring CpGs become more complex without evidence of continuous pattern development and without association to oligoclonal subpolulations of MSCs at later passages. Circularized chromatin conformation capture (4C) revealed reproducible changes in nuclear organization between early and late passages, while there was no preferential interaction with other genomic regions that also harbor culture-associated DNAm changes. Chromatin immunoprecipitation of CTCF did not show significant differences during long-term culture of MSCs, however culture-associated hypermethylation was enriched at CTCF binding sites and hypomethylated CpGs were devoid of CTCF. Taken together, our results indicate that DNAm changes during culture-expansion resembles epigenetic drift, which seems to occur in relation to chromatin conformation.

genomics↗