Schactler, S. A. | Search bioRxiv

bioRxiv2025

Xist Repeat A coordinates an assembly of SR proteins to recruit SPEN and induce gene silencing

The lncRNA Xist represents a paradigm to understand the mechanisms of RNA-mediated gene silencing in mammals, which remain largely unresolved. To induce silencing, Xist recruits the RNA-binding protein SPEN through its 5'-proximal Repeat A domain. Yet, how Repeat A recruits SPEN and how SPEN coordinates silencing remain unclear. We report that sequences in Repeat A critical for SPEN recruitment directly bind SR-rich splicing factors. SRSF1, one such factor, is required for optimal SPEN recruitment and its RS-domain recruits SPEN when tethered to Xist. SPEN and SR-protein-binding motifs promote Repeat As association with many proteins, including the m6A machinery and elongating RNA polymerase II. SPEN also represses autosomal genes where its recruitment coincides with SR-protein binding. Our results reveal an unexpectedly essential role for splicing factors in coordinating silencing by Xist and suggest that the sensing of SR-protein-rich assemblies is a general mechanism through which SPEN targets genes for repression.

genetics↗

bioRxiv2022

CryoGrid-PIXUL-RNA: High throughput RNA isolation platform for tissue transcript analysis

Disease molecular complexity requires high throughput workflows to map disease pathways through analysis of vast tissue repositories. Great progress has been made in life sciences analytical technologies. To match the high throughput of these advanced analytical platforms, we have previously developed a multipurpose microplate sonicator, PIXUL, that can be used in multiple workflows to extract analytes from cultured cells and tissue fragments for various downstream molecular assays. And yet, the sample preparation devices, such as PIXUL, along with the downstream analytical capabilities have not been fully exploited to interrogate tissues because storing and sampling of such specimens remain, in comparison, inefficient. To mitigate this bottleneck, we have developed a low-cost user-friendly system, the CryoGrid, that consists of CryoBlock, thermometer/thermocouple, and QR coded CryoTrays to freeze and store frozen tissue fragments, and hand-held CryoCore tool for tissue sampling supported by iPad and Google apps to display tissues, direct coring and share metadata. RNA is one of the most studied analytes. There is a decades-long history of developing methods to isolate and analyze RNA. Still, the throughput of sampling and RNA extraction from tissues has not matched that of the high throughput transcriptome analytical platforms. To address this need, we have integrated the CryoGrid system with PIXUL-based methods to isolate RNA for gene-specific qPCR and genome-wide transcript analyses. TRIzol is commonly used to isolate RNA but it is labor-intensive, hazardous, requires fume-hoods, and is an expensive reagent. We developed a PIXUL-based TRIzol-free RNA isolation fast protocol that uses a buffer containing proteinase K (PK). Virtually every disease (and often therapeutic agents toxicity) is a systemic syndrome but often only one organ is examined. CryoGrid-PIXUL, integrated with either TRIzol or PK buffer RNA isolation protocols, yielded similar RNA profiles in a multiorgan (brain, heart, kidney and liver) mouse model of sepsis. Thus, RNA isolation using the CryoGrid-PIXUL system combined with the PK buffer offers an inexpensive user-friendly workflow to study transcriptional responses in tissues in health and disease as well as in therapeutic interventions.

molecular biology↗