Nuclear Speckles: Dynamic Hubs of Gene Regulation

Nuclear speckles are highly conserved, membrane-less organelles found within the nuclei of eukaryotic cells. Enriched in RNA-binding proteins, splicing factors, and other regulatory molecules, nuclear speckles are dynamic biomolecular condensates formed through multivalent molecular interactions and liquid–liquid phase separation. Two large scaffold proteins, SON and SRRM2, play central roles in maintaining their structural integrity and dynamic properties. Traditionally viewed as storage and assembly sites for RNA-processing factors, nuclear speckles are now recognized as important regulatory hubs that coordinate multiple aspects of gene expression, including transcription, RNA splicing, RNA processing, and export. Emerging evidence also reveals that nuclear speckles are intimately associated with the three-dimensional organization of the genome, preferentially interacting with transcriptionally active, gene-rich chromatin regions. Their dynamic interactions with chromatin and regulatory proteins help coordinate gene expression programs in response to developmental and environmental cues. Beyond their roles in RNA metabolism, nuclear speckles are increasingly implicated in cellular stress responses, protein homeostasis (proteostasis), aging, and neurological diseases. Understanding how nuclear speckles form, function, and communicate with the genome is therefore fundamental to uncovering how cells maintain homeostasis and how disruption of nuclear organization contributes to human disease.

An analogy would be the water level fluctuations in a lake: Nuclear speckles with higher SON level is like a lake filled with free-flowing water with fast dynamics, while those with reduced SON expression resemble a nearly dried-out lake with a few disconnected pools of stagnant water. We hypothesize that converting stagnant to fluid nuclear speckles may boost proteostasis to slow down aging and aging-related diseases.

We are currently using cutting-edge technologies to study how the nuclear speckle compositions, phase separation dynamics, and chromatin binding status responds to fluctuating proteostatic stress to modulate genetic information flow under both normal physiological and pathological conditions. 

Further readings:

Dion et al., Science Advances, 2022.

UPMC news coverage of our work

Maintaining proper protein folding, trafficking, and turnover—collectively known as proteostasis—is crucial for cellular health. Disruptions in proteostasis, such as the accumulation of misfolded proteins, are implicated in various pathological conditions, including aging and neurodegeneration. To uphold proteome integrity, organisms employ a spectrum of protein quality control mechanisms, encompassing the ubiquitin-proteasome system (UPS), the ER-Golgi protein secretory pathways, ribosome quality control, and the autophagy-lysosomal pathway (ALP). While significant strides have been made in understanding these mechanisms individually, elucidating how they are coordinated across diverse cellular compartments both spatially and temporally remains a formidable challenge. Unraveling the mechanisms governing this spatiotemporal coordination is paramount. Identifying a central regulatory hub overseeing all protein quality control processes not only deepens our comprehension of proteostasis regulation but also unveils potential therapeutic targets. Targeting such a hub could simultaneously engage multiple quality control mechanisms, offering a more effective approach to addressing proteinopathies and aging-related ailments.

      Recent findings have overturned the prevailing notion that protein quality control operates at a steady state under physiological conditions. Instead, we have discovered a 12-hour ultradian oscillator governing mammalian proteostasis gene expression independently of the 24-hour circadian clock and the cell cycle. This oscillator peaks at dawn and dusk, coinciding with heightened metabolic and proteostatic stress. Our investigations into this oscillator have unveiled an unexpected role for nuclear speckles—membrane-less organelles traditionally viewed as facilitating mRNA processing and gene regulation. Contrary to their previous characterization as simple "housekeeping" condensates, nuclear speckles emerge as pivotal sensors of proteostatic stress, orchestrating rapid stress responses by temporally coordinating the global transcriptional activation of proteostasis genes.

      Over the next few years, our research aims to develop innovative tools to dissect how nuclear speckles detect proteostatic stress and regulate temporal proteostasis dynamics. Ultimately, we aspire to leverage this knowledge to devise novel therapeutic strategies for proteinopathies and aging-related diseases, with the goal of alleviating their burdens on human health.

      In a recent endeavor, we identify pyrvinium pamoate as a nuclear speckle rehabilitator that  enhances protein quality control gene expression and suppresses YAP1  transcriptional activity via decreasing the surface/interfacial tension  of nuclear speckle condensates through interaction with the  intrinsically disordered region of nuclear speckle scaffold protein SON.  In pre-clinical models, nanomolar pyrvinium pamoate protects against  retinal degeneration and tauopathy mainly by promoting autophagy and  ubiquitin-proteasome activity in a SON-dependent manner without causing  stress. Aberrant nuclear speckle morphology, reduced protein quality  control and increased YAP1 activity are observed in human tauopathies.  Our study provides proof-of-principle of targeting nuclear speckles to  ameliorate proteinopathies. 

Further readings:

Dion et al., Nature Communications, 2025

A taijitu-inspired schematic illustrates the roles of nuclear speckles in neurons. In the ‘healthy neuron’ state (light half), nuclear speckles (yellow) are enlarged, less spherical, and structurally intact, supporting efficient RNA splicing, robust proteostasis, and stress response capacity, thereby suppressing protein aggregation (blue). In contrast, in the ‘degenerative neuron’ state (dark half), protein aggregates mislocalize nuclear speckle components (such as Serine/Arginine Repetitive Matrix 2 (SRRM2)) to the cytosol, leading to smaller and more spherical nuclear speckles with compromised integrity. This disruption impairs RNA splicing fidelity and stress resilience while increasing the propensity for protein aggregation. The accompanying table summarizes these contrasting features, highlighting the tug-of-war between nuclear speckle integrity and proteotoxic stress that ultimately shapes neuronal fate. SRRM2: Serine/Arginine Repetitive Matrix 2. 

Further readings:

Chen, X. and Zhu, B. Trends in Neurosciences, 2026.