Biology subjects

Sanchez-Velasquez, J.

Publications and source records attributed to Sanchez-Velasquez, J..

2 recordsLinked to original sources

bioRxiv2026

Single-molecule bouncing at a liquid interface governs presynaptic enrichment

Many cellular processes rely on accumulating highly diffusive cytoplasmic proteins to a specific location within the cell. This spatial enrichment is generally thought to rely on locally immobilizing proteins or slowing diffusion through binding and molecular crowding. Paradoxically, cytoplasmic proteins that are enriched within nerve terminals remain highly diffusive, raising questions about the mechanisms that govern presynaptic enrichment. Here, using in vivo single-molecule microscopy, we tracked the diffusion of a model cytoplasmic protein, -Synuclein (-Syn), and synaptic vesicles (SVs), in motor neuron presynapses of live Drosophila larvae. We demonstrate that -Syn undergoes rapid and frequent "bouncing" events at a presynaptic interface, locally impeding escape from the presynapse. We measured escape probabilities at the interface, and show that impeding escape, without dramatically slowing diffusion, is sufficient to govern presynaptic enrichment. The interface is liquid-like and coincides with the boundary of the SV cluster, which is a necessary scaffold for the presynaptic enrichment of -Syn. Our results provide direct evidence of interfacial reflectivity at the interface of liquid-like compartments, and that this phenomenon can govern the subcellular enrichment of proteins and small organelles at the level of individual particles.

neuroscience↗

bioRxiv2026

SMCHD1's DNA binding activity enables its stable retention on chromatin

Chromatin proteins play critical roles in gene regulation, yet frequently we do not fully understand how weak DNA binding affinity of such proteins contributes to their locus-specific actions. Here, we studied SMCHD1, a non-canonical SMC-family protein involved in three-dimensional genome organization and gene repression of the inactive X chromosome and its autosomal targets. We replaced endogenous SMCHD1 with GFP-tagged wild-type or hinge-domain DNA-binding mutant SMCHD1 to define the cellular role of DNA binding. The mutant showed reduced enrichment at the inactive X chromosome in female cells, while retaining stable binding at most autosomal binding sites. Impaired DNA binding weakens SMCHD1-mediated gene repression and chromatin-state regulation, producing hypomorphic effect. Multiple live-cell imaging methods reveal that DNA binding constrains SMCHD1 mobility and supports maintenance, rather than initial recruitment, of chromatin-bound SMCHD1 both during interphase and mitosis. Thus, SMCHD1's weak and sequence-independent DNA binding is a key determinant of its chromatin residence, localization and function. Our findings provide a framework for understanding SMCHD1 and other chromatin proteins with sequence-independent DNA binding activity.

genomics↗