Biology subjects

Ibrahim, D. M.

Publications and source records attributed to Ibrahim, D. M..

6 recordsLinked to original sources

bioRxiv2025

Enhancer-promoter compatibility is mediated by the promoter-proximal region

Gene promoters induce transcription in response to distal enhancers. How enhancers specifically activate their target promoter while bypassing other promoters remains unclear. Here, we find that the promoter-proximal region is critical for cell-type specific enhancer-promoter compatibility. Using high-throughput genome-engineering in mouse embryonic stem cells (mESC), we systematically replace the endogenous Sox9 promoter with different libraries of core and extended (i.e. full) promoters and assess their response to long-range regulatory elements in mESCs and neural progenitor cells. We find that only a subset of full promoters is activated by distal neuronal enhancers and that the promoter-proximal region is necessary for this enhancer-promoter compatibility. Core promoters alone are insufficient to respond to distal enhancers but modulate the transcriptional output of responsive promoters. Our results suggest that within multipartite regulatory domains, the promoter-proximal region fulfills a facilitator-like function that filters and transmits signal from distal enhancers, ultimaltely conferring enhancer-promoter compatibility.

genetics↗

bioRxiv2025

Osmotic niche changes as multifaceted trigger of cellular regenerative processes in organ injury

Cell niches are organ-specific and characterized by a variety of distinct biophysical cues, including mechanics and osmolality. Injury disrupts this cellular environment and marks the start of regenerative processes. It remains unclear whether bone fracture alters the osmolality of bone marrow, and how associated changes in the extracellular matrix (ECM) affect marrow-resident cells in the onset of regeneration. Here we present analyses of human tissue samples indicating that osmolality differences among tissue types lead to a sudden drop in bone marrow osmolality upon fracture, which in turn enhances ECM viscoelasticity. We reveal that a sudden osmolality drop, mimicked in vitro by lowering ion concentrations, triggers bone regenerative processes in mesenchymal stromal cells (MSCs), markedly enhancing their spreading, proliferation, and osteogenic differentiation while residing in osmolality- responsive viscoelastic ECM. Conversely, in non-physiologically elastic ECM, similarly increased osmolality augments MSC osteogenic differentiation, suggesting that ECM viscous dissipation redirects cellular responses to osmotic changes. Mechanistically, the regenerative function of the osmolality drop depends on the matrix providing cell-adhesion ligands and physiological viscoelastic properties. Sequencing data show altered gene expression already two hours after differentiation start, with distinct characteristics related to chromatin structural changes specifically associated with hypoosmolality. Our results suggest that the osmolality drop serves as fast-acting regenerative stimulus for MSCs by extracellularly enhancing matrix viscoelasticity, while altering chromatin structure intracellularly. This stimulus upon injury potentially orchestrates the individual responses of multiple cell types within a niche, facilitating a collective action towards regeneration. Learning how to leverage osmotic cues to induce regenerative cascades may eventually advance local and personalized therapeutic strategies for patients with impaired healing capacity. We anticipate that the integration of osmotic and mechanical ECM properties, as demonstrated in our assay, will catalyze advanced 3D cell culture systems and offer new perspectives on material design in tissue engineering, disease modeling, and mechanobiology.

bioengineering↗

bioRxiv2025

Versatile and efficient non-viral integration of large transgenes in human T cells via CRISPR knock-in and engineered integrases

Current gene transfer methods often lack the precision, versatility, or efficiency when integrating large transgenes, limiting the ability to engineer therapeutic T-cells with more complex payloads. Here, we report one-pot PASTA (Programmable and Site-specific Transgene Addition), a non-viral genome engineering strategy for large gene insertion that combines CRISPR-Cas-mediated homology-directed repair (HDR) and site-specific recombination via serine integrases. Using one-pot PASTA with the Bxb1 integrase, we demonstrate efficient integration of transgenes at multiple genomic loci relevant for T-cell engineering (e.g., TRAC, B2M, CD3E, CD3Z, GAPDH). For constructs > 8 kb, one-pot PASTA outperforms conventional HDR by 19-fold on average and prime-editing-assisted site-specific integrase gene editing (PASSIGE) by 5-fold. This enables the delivery of multi-cistronic cargo to generate dual-antigen targeting CAR T-cells with a safety-switch that overcome antigen escape in lymphoma models. Finally, one-pot PASTA can be further optimized with improved integrase enzymes, such as engineered variants of Pa01 or Bxb1, and plasmids with minimized backbones. In summary, one-pot PASTA represents a versatile and scalable platform for precise, non-viral gene insertion in T-cells.

synthetic biology↗

bioRxiv2024

Conservation of Regulatory Elements with Highly Diverged Sequences Across Large Evolutionary Distances

Embryonic gene expression is remarkably conserved across vertebrates as observed, for instance, in the developing hearts of chicken and mouse which diverged >300 million years ago. However, most cis regulatory elements (CREs) are highly divergent, which makes orthology tracing based on sequence similarity difficult, especially at larger evolutionary distances. Some evidence suggests functional conservation of CREs despite sequence divergence. However, it remains unclear how widespread such functional conservation might be. Here, we address this question by profiling the regulatory genome in the embryonic hearts of chicken and mouse at equivalent developmental stages. Gene expression and 3D chromatin structure show remarkable similiarity, while the majority of CREs are non-alignable between the two species. To identify orthologous CREs independent of sequence alignability, we introduce a synteny-based strategy called Interspecies Point Projection (IPP). Compared to alignment-based approaches, IPP identifies up to 5-fold more putative orthologs in chicken, and up to 9-fold across distantly related vertebrates. We term these sequence-diverged orthologs indirectly conserved and characterize their functional conservation compared to sequence-alignable, directly conserved CREs. Indirectly and directly conserved elements show similar enrichment of functional chromatin signatures and cell-type specific enhancer sequence composition. Yet, shared transcription factor binding sites between orthologs are more heavily rearranged in indirectly conserved elements. Finally, we validate functional conservation of indirectly conserved chicken enhancers in mouse using in vivo reporter assays. Taken together, by overcoming the limitations of alignment-based methods our results reveal functional conservation of CREs across large evolutionary distances is more widespread than previously recognized.

genetics↗

bioRxiv2019

Functional dissection of TADs reveals non-essential and instructive roles in regulating gene expression

The genome is organized in megabase-sized three-dimensional units, called Topologically Associated Domains (TADs), that are separated by boundaries. TADs bring distant cis-regulatory elements into proximity, a process dependent on the cooperative action of cohesin and the DNA binding factor CTCF. Surprisingly, genome-wide depletion of CTCF has little effect on transcription, yet structural variations affecting TADs have been shown to cause gene misexpression and congenital disease. Here, we investigate TAD function in vivo in mice by systematically editing components of TAD organization at the Sox9/Kcnj locus. We find that TADs are formed by a redundant system of CTCF sites requiring the removal of all major sites within the TAD and at the boundary for two neighboring TADs to fuse. TAD fusion resulted in leakage of regulatory activity from the Sox9 to the Kcnj TAD, but no major changes in gene expression. This indicates that TAD structures provide robustness and precision, but are not essential for developmental gene regulation. Gene misexpression and resulting disease phenotypes, however, were attained by re-directing regulatory activity through inversions and/or the re-positioning of boundaries. Thus, efficient re-wiring of enhancer promoter interaction and aberrant disease causing gene activation is not induced by a mere loss of insulation but requires the re-direction of contacts.

genetics↗

bioRxiv2019

Crowdfunded whole-genome sequencing of the celebrity cat Lil BUB identifies causal mutations for her osteopetrosis and polydactyly

Rare diseases and their underlying molecular causes are often poorly studied, posing challenges for patient diagnosis and prognosis. The development of next-generation sequencing and its decreasing costs promises to alleviate such issues by supplying personal genomic information at a moderate price. Here, we used crowdfunding as an alternative funding source to sequence the genome of Lil BUB, a celebrity cat affected by rare disease phenotypes characterized by supernumerary digits, osteopetrosis and dwarfism, all phenotypic traits that also occur in human patients. We discovered that Lil BUB is affected by two distinct mutations: a heterozygous mutation in the limb enhancer of the Sonic hedgehog gene, previously associated with polydactyly in Hemingway cats; and a novel homozygous frameshift deletion affecting the TNFRSF11A (RANK) gene, which has been linked to osteopetrosis in humans. We communicated the progress of this project to a large online audience, detailing the inner workings of personalized whole genome sequencing with the aim of improving genetic literacy. Our results highlight the importance of genomic analysis in the identification of disease-causing mutations and support crowdfunding as a means to fund low-budget projects and as a platform for scientific communication.

genetics↗