Adherens junctions and stem cells

An RNA Polymerase III General Transcription Factor Engages in Cell Type-Specific Chromatin Looping

Transcription factors (TFs) bind DNA in a sequence-specific manner and are generally cell type-specific factors and/or developmental master regulators. In contrast, general TFs (GTFs) are part of very large protein complexes and serve for RNA polymerases’ recruitment to promoter sequences, generally in a cell type-independent manner. Whereas, several TFs have been proven to serve as anchors for the 3D genome organization, the role of GTFs in genome architecture have not been carefully explored. Here, we used ChIP-seq and Hi-C data to depict the role of TFIIIC, one of the RNA polymerase III GTFs, in 3D genome organization. We find that TFIIIC genome occupancy mainly occurs at specific regions, which largely correspond to Alu elements; other characteristic classes of repetitive elements (REs) such as MIR, FLAM-C and ALR/alpha are also found depending on the cell’s developmental origin. The analysis also shows that TFIIIC-enriched regions are involved in cell type-specific DNA looping, which does not depend on colocalization with the master architectural protein CTCF. This work extends previous knowledge on the role of TFIIIC as a bona fide genome organizer whose action participates in cell type-dependent 3D genome looping via binding to REs.

Single-cell transcriptomic profiling of satellite glial cells in stellate ganglia reveals developmental and functional axial dynamics

Stellate ganglion neurons, important mediators of cardiopulmonary neurotransmission, are surrounded by satellite glial cells (SGCs), which are essential for the function, maintenance, and development of neurons. However, it remains unknown whether SGCs in adult sympathetic ganglia exhibit any functional diversity, and what role this plays in modulating neurotransmission. We performed single-cell RNA sequencing of mouse stellate ganglia (n = 8 animals), focusing on SGCs (n = 11,595 cells). SGCs were identified by high expression of glial-specific transcripts, S100b and Fabp7. Microglia and Schwann cells were identified by expression of C1qa/C1qb/C1qc and Ncmap/Drp2, respectively, and excluded from further analysis. Dimensionality reduction and clustering of SGCs revealed six distinct transcriptomic subtypes, one of which was characterized the expression of pro-inflammatory markers and excluded from further analyses. The transcriptomic profiles and corresponding biochemical pathways of the remaining subtypes were analyzed and compared with published astrocytic transcriptomes. This revealed gradual shifts of developmental and functional pathways across the subtypes, originating from an immature and pluripotent subpopulation into two mature populations of SGCs, characterized by upregulated functional pathways such as cholesterol metabolism. As SGCs aged, these functional pathways were downregulated while genes and pathways associated with cellular stress responses were upregulated. These findings were confirmed and furthered by an unbiased pseudo-time analysis, which revealed two distinct trajectories involving the five subtypes that were studied. These findings demonstrate that SGCs in mouse stellate ganglia exhibit transcriptomic heterogeneity along maturation or differentiation axes. These subpopulations and their unique biochemical properties suggest dynamic physiological adaptations that modulate neuronal function.

Cell-cell junctions: structure and regulation in physiology and pathology

Epithelial and endothelial cell-cell contacts are established and maintained by several intercellular junctional complexes. These structurally and biochemically differentiated regions on the plasma membrane primarily include tight junctions (TJs), and anchoring junctions. While the adherens junctions (AJs) provide essential adhesive and mechanical properties, TJs hold the cells together and form a near leak-proof intercellular seal by the fusion of adjacent cell membranes. AJs and TJs play essential roles in vascular permeability. Considering their involvement in several key cellular functions such as barrier formation, proliferation, migration, survival, and differentiation, further research is warranted on the composition and signaling pathways regulating cell-cell junctions to develop novel therapeutics for diseases such as organ injuries. The current review article presents our current state of knowledge on various cell-cell junctions, their molecular composition, and mechanisms regulating their expression and function in endothelial and epithelial cells.

Endothelial progenitor cells enhance blood-brain barrier permeability in subacute stroke

OBJECTIVE

To study the association among endothelial progenitor cells (EPCs), subacute blood-brain barrier (BBB) permeability, and clinical outcome after ischemic stroke, determining the micro RNAs of EPCs responsible for good clinical outcome.

METHODS

We included consecutive patients with nonlacunar acute ischemic strokes in the territory of a middle cerebral artery and ages between 18 and 80 years. Clinical outcome was defined as modified Rankin Scale score at 3 months. Neuroimaging was performed at day 0 and 7 by MRI, including assessment of BBB permeability by dynamic contrast enhancement. EPCs were isolated from peripheral venous blood, quantified, and submitted to in vitro functional tests, including migratory and angiogenic assays. Stroke hemodynamics were evaluated serially by ultrasound. Statistical significance was set at p < 0.05.

RESULTS

We included 45 patients; mean age was 70.0 ± 10.0 years. The in vitro functional properties of EPCs were associated with BBB permeability, particularly at day 7. The number of each EPC subset at both timepoints was not associated with BBB permeability. Permeability of BBB at day 7 was independently associated with improved clinical outcome (odds ratio 0.897; 95% confidence interval 0.816-0.986; p = 0.025). The EPCs (CD34+ cell subset) of patients with good clinical outcome showed 24 differentially expressed miRNAs, with a common effect on adherens junction pathway.

CONCLUSIONS

The functional properties of EPCs are associated with enhanced subacute permeability of BBB and improved clinical outcome after acute ischemic stroke.

Water transport through the intestinal epithelial barrier under different osmotic conditions is dependent on LI-cadherin trans-interaction

In the intestine water has to be reabsorbed from the chymus across the intestinal epithelium. The osmolarity within the lumen is subjected to high variations meaning that water transport often has to take place against osmotic gradients. It has been hypothesized that LI-cadherin is important in this process by keeping the intercellular cleft narrow facilitating the buildup of an osmotic gradient allowing water reabsorption. LI-cadherin is exceptional among the cadherin superfamily with respect to its localization along the lateral plasma membrane of epithelial cells being excluded from adherens junction. Furthermore it has 7 but not 5 extracellular cadherin repeats (EC1-EC7) and a small cytosolic domain. In this study we identified the peptide VAALD as an inhibitor of LI-cadherin trans-interaction by modeling the structure of LI-cadherin and comparison with the known adhesive interfaces of E-cadherin. This inhibitory peptide was used to measure LI-cadherin dependency of water transport through a monolayer of epithelial CACO2 cells under various osmotic conditions. If LI-cadherin trans-interaction was inhibited by use of the peptide, water transport from the luminal to the basolateral side was impaired and even reversed in the case of hypertonic conditions whereas no effect could be observed at isotonic conditions. These data are in line with a recently published model predicting LI-cadherin to keep the width of the lateral intercellular cleft small. In this narrow cleft a high osmolarity can be achieved due to ion pumps yielding a standing osmotic gradient allowing water absorption from the gut even if the faeces is highly hypertonic.

Single-Cell Lineage Tracing Reveals that Oriented Cell Division Contributes to Trabecular Morphogenesis and Regional Specification

The cardiac trabeculae are sheet-like structures extending from the myocardium that function to increase surface area. A lack of trabeculation causes embryonic lethality due to compromised cardiac function. To understand the cellular and molecular mechanisms of trabecular formation, we genetically labeled individual cardiomyocytes prior to trabeculation via the brainbow multicolor system and traced and analyzed the labeled cells during trabeculation by whole-embryo clearing and imaging. The clones derived from labeled single cells displayed four different geometric patterns that are derived from different patterns of oriented cell division (OCD) and migration. Of the four types of clones, the inner, transmural, and mixed clones contributed to trabecular cardiomyocytes. Further studies showed that perpendicular OCD is an extrinsic asymmetric cell division that putatively contributes to trabecular regional specification. Furthermore, N-Cadherin deletion in labeled clones disrupted the clonal patterns. In summary, our data demonstrate that OCD contributes to trabecular morphogenesis and specification.

Possible roles of LI-Cadherin in the formation and maintenance of the intestinal epithelial barrier

LI-cadherin belongs to the so called 7D-cadherins, exceptional members of the cadherin superfamily which are characterized by seven extracellular cadherin repeats and a small cytosolic domain. Under physiological conditions LI-cadherin is expressed in the intestine and colon in human and mouse and in the rat also in hepatocytes. LI-cadherin was shown to act as a functional Ca²⁺-dependent adhesion molecule, linking neighboring cells and a lot of biophysical and biochemical parameters were determined in the last time. It is also known that dysregulated LI-cadherin expression can be found in a variety of diseases. Although there are several hypothesis and theoretical models concerning the function of LI-cadherin, the physiological role of LI-cadherin is still enigmatic.

An introduction to adherens junctions: from molecular mechanisms to tissue development and disease

Adherens junctions (AJs) are fundamental for the development of animal tissues and organs. The core complex is formed from transmembrane cell-cell adhesion molecules, cadherins, and adaptor molecules, the catenins, that link to cytoskeletal and regulatory networks within the cell. This complex can be considered over a wide range of biological organization, from atoms to molecules, protein complexes, molecular networks, cells, tissues, and overall animal development. AJs have also been an integral part of animal evolution, and play central roles in cancer development and pathogen infection. This book addresses major questions encompassing these aspects of AJ biology. How did AJs evolve? How do the cadherins and catenins interact to assemble AJs and mediate adhesion? How do AJs interface with other cellular machinery to couple adhesion with the whole cell? How do AJs affect cell behaviour and multicellular development? How can abnormal AJ activity lead to disease?