Cells of multicellular organisms need to communicate with each other and have evolved various mechanisms for this purpose, the most direct and quickest of which is through channels that directly ...connect the cytoplasms of adjacent cells. Such intercellular channels span the two plasma membranes and the intercellular space and result from the docking of two hemichannels. These channels are densely packed into plasma-membrane spatial microdomains termed “gap junctions” and allow cells to exchange ions and small molecules directly. A hemichannel is a hexameric torus of junctional proteins around an aqueous pore. Vertebrates express two families of gap-junction proteins: the well-characterized connexins and the more recently discovered pannexins, the latter being related to invertebrate innexins (“invertebrate connexins”). Some gap-junctional hemichannels also appear to mediate cell-extracellular communication. Communicating junctions play crucial roles in the maintenance of homeostasis, morphogenesis, cell differentiation and growth control in metazoans. Gap-junctional channels are not passive conduits, as previously long regarded, but use “gating” mechanisms to open and close the central pore in response to biological stimuli (e.g. a change in the transjunctional voltage). Their permeability is finely tuned by complex mechanisms that have just begun to be identified. Given their ubiquity and diversity, gap junctions play crucial roles in a plethora of functions and their dysfunctions are involved in a wide range of diseases. However, the exact mechanisms involved remain poorly understood.
Communication is important to ensure the correct and efficient flow of information, which is required to sustain active social networks. A fine-tuned communication between cells is vital to maintain ...the homeostasis and function of multicellular or unicellular organisms in a community environment. Although there are different levels of complexity, intercellular communication, in prokaryotes to mammalians, can occur through secreted molecules (either soluble or encapsulated in vesicles), tubular structures connecting close cells or intercellular channels that link the cytoplasm of adjacent cells. In mammals, these different types of communication serve different purposes, may involve distinct factors and are mediated by extracellular vesicles, tunnelling nanotubes or gap junctions. Recent studies have shown that connexin 43 (Cx43, also known as GJA1), a transmembrane protein initially described as a gap junction protein, participates in all these forms of communication; this emphasizes the concept of adopting strategies to maximize the potential of available resources by reutilizing the same factor in different scenarios. In this Review, we provide an overview of the most recent advances regarding the role of Cx43 in intercellular communication mediated by extracellular vesicles, tunnelling nanotubes and gap junctions.
Natural disturbances are important drivers of forest dynamics, and canopy gaps are their fingerprints in forest ecosystems. Gaps form and persist because of the interplay of tree mortality and ...regeneration. They can have long‐lasting impacts on ecosystems, yet the temporal dynamics of gap formation and closure remains poorly quantified.
We analysed 11,331 canopy gaps and their changes through time across 3999 ha of unmanaged temperate mountain forests at Berchtesgaden National Park (Germany). We assessed gap formation and closure using three repeat lidar acquisitions between 2009 and 2021, analysing canopy height changes at 1 m horizontal resolution. Our objective was to determine the dominant mode of gap formation, distinguishing the creation of new gaps from the expansion of existing ones. Additionally, we studied the rate of gap closure, considering closure from tree regeneration and lateral crown expansion.
Gap formation was primarily driven by gap expansion rather than the initiation of new gaps. Gap expansion accounted for 81.3% of gap formation, although new gaps were on average twice as large as gap expansions. Only 1.4% of gaps did not expand over the 12‐year study period, and Norway spruce forests had the highest rate of gap expansion.
Overall, gap closure rate (0.74 ha 100 ha−1 year−1) was higher than gap formation (0.58 ha 100 ha−1 year−1) in our study system. Ingrowth of the regenerating tree cohort was the primary mode of gap closure, with lateral crown expansion accounting for 20% of all gap area closed. Mixed‐species stands had the highest rate of gap closure, and gaps <0.1 ha closed faster than larger gaps.
Synthesis. While canopy openings are generally small in the European Alps, we show that they keep growing over multiple years, underlining that gap expansion is an important driver of temperate forest dynamics. Canopy gaps closed faster than they were created, highlighting the resilience of European mountain forests to natural disturbances. However, as disturbances are projected to increase under climate change, this resilience might be challenged in the future, requiring a continuous monitoring of gap dynamics as an important early warning indicator of forest change.
Zusammenfassung
Natürliche Störungen sind wichtige Treiber der Walddynamik, und Lücken im Kronendach sind ihre „Fingerabdrücke“ in Waldökosystemen. Lücken entstehen aufgrund des Zusammenspiels von Baumsterben und Baumverjüngung. Sie können langanhaltende Auswirkungen auf Ökosysteme haben, doch die zeitliche Dynamik der Lückenbildung und des Lückenschlusses ist nach wie vor kaum quantifiziert.
Wir analysierten 11.331 Lücken im Kronendach und ihre zeitlichen Veränderungen auf 3.999 ha unbewirtschafteter Bergwälder der gemäßigten Zone im Nationalpark Berchtesgaden (Deutschland). Wir quantifizierten die Bildung und Schließung von Lücken anhand von drei wiederholten Lidar‐Aufnahmen zwischen 2009 und 2021 und analysierten die Veränderungen der Baumhöhe mit einer horizontalen Auflösung von 1 m. Unser Ziel war es, den vorherrschenden Modus der Lückenbildung zu bestimmen und dabei die Entstehung neuer Lücken von der Ausdehnung bestehender Lücken zu unterscheiden. Außerdem untersuchten wir die Rate des Lückenschlusses, wobei wir Lückenschluss durch Baumverjüngung und seitliche Kronenausdehnung berücksichtigten.
Die Lückenbildung wurde in erster Linie durch Lückenerweiterung und nicht durch die Entstehung neuer Lücken bestimmt. Lückenerweiterungen machten 81,3% der Lückenbildung aus, obwohl die neuen Lücken im Durchschnitt doppelt so groß waren wie die Erweiterungen bestehender Lücken. Nur 1,4% der Lücken vergrößerten sich während des 12‐jährigen Untersuchungszeitraums nicht, wobei Fichtenwälder den höchsten Anteil an Lückenvergrößerungen aufwiesen.
Insgesamt war die Lückenschlussrate (0,74 ha 100 ha−1 Jahr−1) in unserem Studiensystem höher als die Rate der Kronenöffnung (0,58 ha 100 ha−1 Jahr−1). Das Einwachsen der sich verjüngenden Baumkohorte war der wichtigste Mechanismus des Lückenschlusses, wobei seitliche Kronenausdehnung 20% der gesamten geschlossenen Lückenfläche ausmachte. Mischbestände wiesen die höchste Lückenschlussrate auf, und Lücken <0,1 ha schlossen sich schneller als größere Lücken.
Synthese. Obwohl die Öffnungen im Kronendach in den europäischen Alpen im Allgemeinen klein sind, zeigen wir, dass sie über mehrere Jahre hinweg wachsen. Das dokumentiert, dass die Ausdehnung von Lücken ein wichtiger Mechanismus in der Dynamik gemäßigter Wälder ist. Lücken im Kronendach schließen sich schneller als sie entstehen, was die Resilienz europäischer Bergwälder gegenüber natürlichen Störungen unterstreicht. Da jedoch prognostiziert wird, dass Störungen im Zuge des Klimawandels deutlich zunehmen werden, könnte diese Resilienz in Zukunft in Frage gestellt werden, was eine kontinuierliche Überwachung der Lückendynamik als wichtigen Frühwarnindikator für Waldveränderungen erfordert.
Canopy gaps are the fingerprints of forest disturbances. The authors analysed 11,331 canopy gaps and their changes through time across 3999 ha of unmanaged temperate mountain forests using three consecutive lidar acquisitions. The gradual expansion of existing gaps is an important—yet often overlooked—driver of temperate forest dynamics. However, gaps closed faster than they were created, indicating high forest resilience (image by Michael Maroschek).
•The first repeated terrestrial canopy gap inventory in a Eur. beech virgin forest.•We found a significant decrease in gap fraction and changes in gap size pattern.•High rates of gap closure were ...found that strongly dominated over gap formation.•There was a shift in the dominant gap filling process with increasing gap size.•Gaps released a heterogeneously structured understory and promoted its height growth.
Canopy gaps play a crucial role for forest dynamics processes, as they largely determine light transmission to lower canopy strata, thereby controlling the turnover of tree individuals in the stand. Even though their functional importance is undisputed, quantitative data on the rate of gap creation and gap closure, and the temporal change in gap size distribution patterns in temperate virgin forests are scarce. We used a repeated inventory (line-intercept sampling) of gap size frequency and fraction in a virgin beech (Fagus sylvatica) forest in the Slovakian Carpathians over a 10-year interval (2003–2013) to test the hypotheses that (i) disturbance intensity and thus gap creation and gap closure rate change only little over time, (ii) gaps persist or even expand, until they are filled primarily by vertical ingrowth of trees from lower strata, and (iii) gap creation promotes the height growth of released saplings and sub-canopy trees. In the 2003 and 2013 inventories, 37 and 30 gaps >20 m2 size were mapped along a total of 3217 m transect line investigated. The large majority of gaps was <100 m2 in size; large gaps >500 m2 were very rare. Gap fraction decreased significantly from 13.6% in 2003 to 8.2% in 2013 (associated with a reduction in mean gap size from 261 to 96 m2), indicating considerable variation in disturbance intensity in the past decades. Before 2003, both large gaps (probably caused by wind throw) and small gaps (from dying trees) have been formed, while only small gaps developed in the period 2003–2013. Small gaps were closed within a few years through rapid horizontal canopy expansion of neighboring beech trees, while vertical gap filling through ingrowth of lower canopy layers and regeneration was the dominant process in larger gaps. Saplings and trees in lower canopy layers formed a heterogeneous understory in large parts of recently formed gaps and responded to this process with increased height growth. We conclude that, despite considerable variation in disturbance intensity over time, this beech virgin forest responds to gap formation with high resilience through rapid lateral canopy expansion in small gaps and ingrowth of saplings and sub-dominant tree layers in larger gaps.
The gap junctions (GJs) formed by Cx40 and Cx43 provide a low resistance passage allowing for rapid propagation of action potentials. Sporadic somatic mutations in GJA5 (encoding Cx40) have been ...identified in lone atrial fibrillation (AF) patients. More recently germline autosomal dominantly inherited mutations in GJA5 have been found in early onset lone AF patients in several families over generations. Characterizations of these AF-linked Cx40 mutants in model cells and in patient tissues revealed that some of the mutants reduced GJ channel function due to an impaired trafficking or channel formation. While others showed a gain-of-function in hemichannels. These functional alterations in GJs or hemichannel may play an important role in the pathogenesis of AF in the mutant carriers.
This study uses survey data from the Pew Internet and American Life Project to advance digital divide research by exploring how smartphone dependence—in which one’s only means of accessing the ...Internet is via a smartphone—and smartphone use differ between key demographic groups in the United States. Results show differences in smartphone dependence and use based on race, age, income, and education. Minority group members, younger, lower income, and less educated users are more likely to be smartphone-dependent. Additionally, minorities and younger individuals use smartphones for more social activity, while White, younger, and higher income individuals use smartphones for more news/information activity. Findings support the usage gap hypothesis and suggest smartphones may act as both a bridge and a barrier for disadvantaged groups to overcome the digital divide.
Gap junctions establish direct pathways for cell-to-cell communication through the assembly of twelve connexin subunits that form intercellular channels connecting neighbouring cells. Co-assembly of ...different connexin isoforms produces channels with unique properties and enables communication across cell types. Here we used single-particle cryo-electron microscopy to investigate the structural basis of connexin co-assembly in native lens gap junction channels composed of connexin 46 and connexin 50 (Cx46/50). We provide the first comparative analysis to connexin 26 (Cx26), which-together with computational studies-elucidates key energetic features governing gap junction permselectivity. Cx46/50 adopts an open-state conformation that is distinct from the Cx26 crystal structure, yet it appears to be stabilized by a conserved set of hydrophobic anchoring residues. 'Hot spots' of genetic mutations linked to hereditary cataract formation map to the core structural-functional elements identified in Cx46/50, suggesting explanations for many of the disease-causing effects.
Air gap membrane distillation (AGMD) and permeate gap membrane distillation (PGMD) were investigated and compared through self-developed hollow fiber membrane modules with internal energy recovery. ...The effects of the feed temperature, the coolant temperature, the flow rate, the gap thermal conductivity, and the gap width on the flux and the gained output ratio (GOR) were evaluated experimentally. The gap between the membrane and the condensing surface was a key factor affecting the flux and the GOR in both AGMD and PGMD. It was found that the improvement of gap thermal conductivity using brass net was useless in improving flux and GOR. The permeate water filled in the gap changed the process of mass and heat transfer in the gap which gave rise to the increase in the flux and thermal recovery. The flux and GOR in PGMD increased by 7.9% and 59.82% in the gap of 0.5mm compared to the AGMD. The salt rejection of all experiments was greater than 99.8%.
•Internal energy recovery hollow fiber membrane modules were assembled.•The influence of permeate gap on mass and heat transfer was investigated.•The flux and GOR increased by 7.9% and 59.82% for PGMD compared to AGMD.
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