Nucleoporin insufficiency disrupts a pluripotent regulatory circuit in a pro-arrhythmogenic stem cell line

From the sideline: Tissue-specific nucleoporin function in health and disease, an update

The subcellular compartmentalisation of eukaryotic cells requires selective exchange between the cytoplasm and the nucleus. Intact nucleocytoplasmic transport is vital for normal cell function and mutations in the executing machinery have been causally linked to human disease. Central players in nucleocytoplasmic exchange are nuclear pore complexes (NPCs), which are built from ~30 distinct proteins collectively termed nucleoporins. Aberrant nucleoporin expression was detected in human cancers and autoimmune diseases since quite some time, while it was through the increasing use of next generation sequencing that mutations in nucleoporin genes associated with mainly rare hereditary diseases were revealed. The number of newly identified mutations is steadily increasing, as is the number of diseases. Mutational hotspots have emerged: mutations in the scaffold nucleoporins seemingly affect primarily inner organs, such as heart, kidney, and ovaries, whereas genetic alterations in peripheral, cytoplasmic nucleoporins affect primarily the central nervous system and development. In this review, we summarise latest insights on altered nucleoporin function in the context of human hereditary disorders, with a focus on those where mechanistic insights are beginning to emerge.

Epigenetic regulation of neural stem cells: The emerging role of nucleoporins

Nucleoporins (Nups) are components of the nuclear pore complex that, besides regulating nucleus-cytoplasmic transport, emerged as a hub for chromatin interaction and gene expression modulation. Specifically, Nups act in a dynamic manner both at specific gene level and in the topological organization of chromatin domains. As such, they play a fundamental role during development and determination of stemness/differentiation balance in stem cells. An increasing number of reports indicate the implication of Nups in many central nervous system functions with great impact on neurogenesis, neurophysiology, and neurological disorders. Nevertheless, the role of Nup-mediated epigenetic regulation in embryonic and adult neural stem cells (NSCs) is a field largely unexplored and the comprehension of their mechanisms of action is only beginning to be unveiled. After a brief overview of epigenetic mechanisms, we will present and discuss the emerging role of Nups as new effectors of neuroepigenetics and as dynamic platform for chromatin function with specific reference to the biology of NSCs.

Expression of NR5A2, NUP153, HNF4A, USP15 and FNDC3B is consistent with their use as novel biomarkers for bovine mammary stem/progenitor cells

Mammary stem cells (MaSC) are essential for growth and maintenance of mammary epithelium. Previous studies have utilized morphological characteristics or retention of bromodeoxyuridine (BrdU) label to identify MaSC and progenitor cells, these approaches may not be feasible or may not identify all resident stem cells. Alternatively, these special cells may be identified by assessing protein and mRNA expression of appropriate markers. The focus of this study was to assess the staining patterns and in situ quantification of novel candidate markers for bovine MaSC/progenitor cells. The candidate markers for MaSC/progenitor cells for immunohistochemical analysis were: NR5A2, NUP153, HNF4A, USP15 and FNDC3B and for in situ transcripts quantification were HNF4A and NUP153. We also evaluated protein expression pattern of presumptive MaSC markers known from the literature namely, ALDH1, MSI1 and Notch3. We found that NR5A2, NUP153, HNF4A and USP15-labeled cells represented 2.5-6% of epithelial cells prepubertally and were distributed in a fashion consistent with the location and abundance of MaSC/progenitor cells. A transient increase (10-37%) in expression of these markers was observed at peak lactation. FNDC3B was localized mainly in the nucleus prepubertally and in the cytoplasm of myoepithelial cells and nuclei of a limited number of alveolar cells during lactation. Abundant expression (~ 48%) and luminal localization of ALDH1 precludes its use as a bovine MaSC marker but may include transamplifying progenitor cells. MSI1 staining was consistent with MaSC localization. Onset of lumen formation in mammary ducts of prepubertal gland was associated with Notch 3 expression in the apical surface of luminal cells. RNAscope analysis of HNF4A and NUP153 transcripts in calf mammary gland showed very low copy numbers in a few epithelial cells, supporting the idea that these markers are expressed by fewer cells of epithelial origin. This study suggests that NR5A2, NUP153, HNF4A, USP15 and FNDC3B are likely markers for bovine MaSC/progenitor cells. Quantification of RNA transcripts of HNF4A and NUP153 in bovine MEC as potential MaSC markers are novel. Further studies to correlate protein expression of these markers with their transcripts level using single cell analysis in larger samples in lactating cow at different physiological stages are warranted.

Nuclear pore complexes in development and tissue homeostasis

Nuclear pore complexes are multiprotein channels that span the nuclear envelope, which connects the nucleus to the cytoplasm. In addition to their main role in the regulation of nucleocytoplasmic molecule exchange, it has become evident that nuclear pore complexes and their components also have multiple transport-independent functions. In recent years, an increasing number of studies have reported the involvement of nuclear pore complex components in embryogenesis, cell differentiation and tissue-specific processes. Here, we review the findings that highlight the dynamic nature of nuclear pore complexes and their roles in many cell type-specific functions during development and tissue homeostasis.

Nucleoporins in cardiovascular disease

Cardiovascular disease is a pressing health problem with significant global health, societal, and financial burdens. Understanding the molecular basis of polygenic cardiac pathology is thus essential to devising novel approaches for management and treatment. Recent identification of uncharacterized regulatory functions for a class of nuclear envelope proteins called nucleoporins offers the opportunity to understand novel putative mechanisms of cardiac disease development and progression. Consistent reports of nucleoporin deregulation associated with ischemic and dilated cardiomyopathies, arrhythmias and valvular disorders suggests that nucleoporin impairment may be a significant but understudied variable in cardiopathologic disorders. This review discusses and converges existing literature regarding nuclear pore complex proteins and their association with cardiac pathologies, and proposes a role for nucleoporins as facilitators of cardiac disease.

Protein Subdomain Enrichment of NUP155 Variants Identify a Novel Predicted Pathogenic Hotspot

Functional variants in nuclear envelope genes are implicated as underlying causes of cardiopathology. To examine the potential association of single nucleotide variants of nucleoporin genes with cardiac disease, we employed a prognostic scoring approach to investigate variants of NUP155, a nucleoporin gene clinically linked with atrial fibrillation. Here we implemented bioinformatic profiling and predictive scoring, based on the gnomAD, National Heart Lung and Blood Institute-Exome Sequencing Project (NHLBI-ESP) Exome Variant Server, and dbNSFP databases to identify rare single nucleotide variants (SNVs) of NUP155 potentially associated with cardiopathology. This predictive scoring revealed 24 SNVs of NUP155 as potentially cardiopathogenic variants located primarily in the N-terminal crescent-shaped domain of NUP155. In addition, a predicted NUP155 R672G variant prioritized in our study was mapped to a region within the alpha helical stack of the crescent domain of NUP155. Bioinformatic analysis of inferred protein-protein interactions of NUP155 revealed over representation of top functions related to molecular transport, RNA trafficking, and RNA post-transcriptional modification. Topology analysis revealed prioritized hubs critical for maintaining network integrity and informational flow that included FN1, SIRT7, and CUL7 with nodal enrichment of RNA helicases in the topmost enriched subnetwork. Furthermore, integration of the top 5 subnetworks to capture network topology of an expanded framework revealed that FN1 maintained its hub status, with elevation of EED, CUL3, and EFTUD2. This is the first study to report novel discovery of a NUP155 subdomain hotspot that enriches for allelic variants of NUP155 predicted to be clinically damaging, and supports a role for RNA metabolism in cardiac disease and development.