Biology subjects

Chapin, N.

Publications and source records attributed to Chapin, N..

4 recordsLinked to original sources

bioRxiv2025

The HMGN Proteins Are Transcriptional Regulatory Factors in Humans

The high mobility group N (HMGN) proteins, which were discovered over 50 years ago, are a multigene family of abundant nucleosome-specific binding factors that are present in all vertebrates. Despite their intriguing nucleosome-binding activity, the potential functions of the HMGN proteins in chromatin have not yet been assessed unambiguously due to the presence of several related HMGN genes in vertebrates and the lack of HMGN null cells. Here, we investigated the genome-wide activities of the human HMGN proteins by generating and analyzing an HMGN null cell line and isogenic HMGN rescue cell lines. These experiments revealed that the HMGN proteins function in the activation of gene expression at the level of transcription initiation at over a thousand specific sites that are mostly in promoters and enhancers. We additionally observed shared as well as unique functions of HMGN1 and HMGN2, which are likely to be the most abundant and ancient HMGN proteins. These findings thus indicate that the HMGN nucleosome-binding proteins are vertebrate-specific regulatory factors that primarily function in the activation of transcription initiation. Hence, any comprehensive model of vertebrate gene regulation should incorporate the contributions of the HMGN proteins, which are integral components of chromatin in all vertebrates.

molecular biology↗

bioRxiv2025

Shear Stress Induces Concentration Gradient Distributions of Membrane Proteins in Live Cells

Cells sense and respond to fluid shear stress. Cell surfaces are exposed to flow, yet the influence of shear stress on the behavior of plasma membrane proteins remains unclear. Here we show that extracellular flow induces the gradient distribution of cell membrane proteins with increasing concentration toward the downstream direction of the flow. Shear stress at 10-30 dynes/cm2 caused formation of concentration gradients of both GPI-anchored proteins and transmembrane proteins, including integrin{beta}1, E-cadherin and the insulin receptor in Xenopus XTC cells. Using single-molecule live-cell imaging, we found that GPI-anchored T-cadherin molecules are dragged along the direction of flow under shear stress. In addition, shear stress induced concentration gradients of membrane proteins in COS-7 cells and human umbilical vein endothelial cells (HUVECs). Our findings suggest that external flow directly transports membrane proteins, establishing concentration gradients that may contribute to the cellular flow-sensing mechanism.

biophysics↗

bioRxiv2021

A versatile active learning workflow for optimization of genetic and metabolic networks

The study, engineering and application of biological networks require practical and efficient approaches. Current optimization efforts of these systems are often limited by wet lab labor and cost, as well as the lack of convenient, easily adoptable computational tools. Aimed at democratization and standardization, we describe METIS, a modular and versatile active machine learning workflow with a simple online interface for the optimization of biological target functions with minimal experimental datasets. We demonstrate our workflow for various applications, from simple to complex gene circuits and metabolic networks, including several cell-free transcription and translation systems, a LacI-based multi-level controller and a 27-variable synthetic CO2-fixation cycle (CETCH cycle). Using METIS, we could improve above systems between one and two orders of magnitude compared to their original setup with minimal experimental efforts. For the CETCH cycle, we explored the combinatorial space of [~]1025 conditions with only 1,000 experiments to yield the most efficient CO2-fixation cascade described to date. Beyond optimization, our workflow also quantifies the relative importance of individual factors to the performance of a system. This allows to identify so far unknown interactions and bottlenecks in complex systems, which paves the way for their hypothesis-driven improvement, which we demonstrate for the LacI multi-level controller that we were able to improve by 34-fold after having identified resource competition as limiting factor. Overall, our workflow opens the way for convenient optimization and prototyping of genetic and metabolic networks with customizable adjustments according to user experience, experimental setup, and laboratory facilities.

synthetic biology↗

bioRxiv2020

Nucleoid openness profiling links bacterial genome structure to phenotype

Gene expression requires specific structural alternations in the nucleoid structure to enable the access of the transcription machinery into the genomic DNA. In prokaryotes, DNA binding proteins, including nucleoid-associated proteins (NAPs) and transcription factors (TFs), drive the change in structure and gene expression. Currently, studies of global NAP and TF binding are often hindered by the lack of appropriate epigenomic tools. Here, we present POP-seq, a method that provides in vivo genome-wide openness profiles of the bacterial nucleoid. We demonstrate that POP-seq can be used to map the global in vivo protein-DNA binding events. Our results highlight a negative correlation between genome openness, compaction and transcription, suggesting that regions that are not accessible to Tn5 transposase are either too compacted or occupied by RNA polymerase. Importantly, we also show that the least open regions are enriched in housekeeping genes, while the most open regions are significantly enriched in genes important for fast adaptation to changing environment. Finally, we demonstrated that the genome openness profile is growth condition specific. Together, those results suggest a model where one can distinguish two types of epigenetic control: one stable, long-term silencing of highly compacted regions, and a second, highly responsive regulation through the dynamic competition between NAPs and RNA polymerase binding. Overall, POP-seq captures structural changes in the prokaryotic chromatin and provides condition-specific maps of global protein-DNA binding events, thus linking overall transcriptional and epigenetic regulation directly to phenotype.

microbiology↗